Towards the minimal amount of exercise for improving metabolic health: beneficial effects of reduced-exertion high-intensity interval training. Eur J Appl Physiol. 2012;112:2767-2775. [PMID: 22124524 DOI: 10.1007/s00421-011-2254-z]

Effects of reduced-exertion high-intensity training versus short moderate-intensity continuous training on biomarkers of mortality risk in sedentary women: A randomized clinical trial

INTRODUCTION

This study aimed to compare the effects of reduced-exertion high-intensity training (REHIT) versus short moderate-intensity continuous training (SMICT) on functional capacity, resting heart rate (RHR), and activity enjoyment in sedentary women.

METHODS

Thirty sedentary young women were randomly allocated to a: i) REHIT group (n = 15) or ii) SMICT group (n = 15) (2 sessions/week, 6 weeks) using a computer-generated random allocation sequence. Both groups performed an intervention on a cycle ergometer that included a warm-up (3 min at 50% of HRmax), the main part of the session, and a cool-down (3 min at 50% of HRmax). The main part in REHIT consists of 20-40 s divided on two maximum cycling sprints of all-out exercise at 100% of HRmax with an active rest of 3 min between them; whilst SMICT consisted of 6-12 min of moderate intensity exercise at 60-70% of HRmax. Functional capacity (6-min walking test) and RHR were measured before and after the intervention. Physical activity enjoyment (Physical Activity Enjoyment Scale) was assessed after the intervention.

RESULTS

The effects of the REHIT on functional capacity showed a significant interaction between time measurement and intervention group (p < 0.001) that not occurred in RHR (p > 0.05). Intragroup post-hoc analysis revealed that both groups improve their values in functional capacity and RHR (p < 0.05). Between-groups comparison showed that REHIT group increased significantly functional capacity more than SMICT (p = 0.002). In addition, physical activity enjoyment scores were high in both groups without differences.

CONCLUSION

REHIT and SMICT are appropriate for improving functional capacity and RHR, as well as being perceived as enjoyable in sedentary young women. REHIT offers higher improvements in functional capacity.

CLINICAL TRIAL REGISTRATION NUMBER

NCT05875051.

Customizing intense interval exercise training prescription using the "frequency, intensity, time, and type of exercise" (FITT) principle

Intense interval exercise training induces various physiological and metabolic adaptations related to performance and health. For designing a program, the F.I.T.T. principle, referring to frequency, intensity, time, and type of exercise, can be used to manipulate the level of physiological stress in the body, leading to various adaptations. Modifying these four parameters results in a wide range of interval protocols that are safe and effective for different populations including athletes and individuals with chronic diseases. In this review, we present how the manipulation of the F.I.T.T. components can alter the acute and chronic cardiorespiratory, metabolic, perceptual, and affective responses and adaptations to intense interval exercise training. From this evidence, it appears that the duration of the exercise bout and recovery interval are critical parameters for the manipulation of almost all acute responses, enabling periodization of intense interval exercise training, and promoting optimal adaptations and exercise adherence. In addition, a considerable level of adaptations may be achieved with training frequencies as low as once or twice per week and with lower than maximal intensities, adding to the feasibility of this exercise mode. Overall, by varying these parameters, the design of an intense interval exercise training program can be tailored according to the needs and abilities of each individual, and an optimized training prescription may be achieved.

High-intensity interval training improves insulin sensitivity in individuals with prediabetes

OBJECTIVE

To examine the separate and combined effects of low-volume high-intensity interval training (HIIT) and walking compared with no training on insulin sensitivity and skeletal metabolic capacity in individuals with prediabetes.

DESIGN

Individuals were randomized to: (1) control (no exercise), (2) HIIT (3 × 20 s's cycle sprint 3 times weekly), (3) HIIT + walking (walking >10 000 steps/day), or (4) walking for 12 weeks.

METHODS

Insulin sensitivity was assessed by an oral glucose tolerance test at baseline and end-of-trial. Additionally, proteins important for mitochondria capacity and insulin sensitivity were measured in the vastus lateralis muscle.

RESULTS

Seventy sedentary individuals with prediabetes (women n = 36; age: 60.8 ± 11.3 years (mean ± SD); body mass index: 31.6 ± 4.4 kg/m2; fasting plasma glucose: 6.6 ± 0.8 mmol/L; glycated hemoglobin A1c 5.7 ± 0.4% (39.0 ± 4.3 mmol/mol) were included. Compared with control, peripheral insulin sensitivity (measured by the Cederholm index) was significantly improved with HIIT (estimated treatment difference [ETD]: 18.5% [95% confidence interval (CI): 7.4; 28.3%] and HIIT + walking [ETD: 15.7% (95% CI: 4.4; 25.6%)]), but not with walking alone (ETD: 9.4% [95% CI: -2.5; 19.9%]). Whole-body insulin sensitivity (measured by the Matsuda index) was significantly increased with HIIT + walking (ETD: 28.0% [95% CI: 10.3; 42.3%]) and walking alone (ETD: 42.3% [95% CI: 28.3; 53.5%]), but not with HIIT alone (ETD: 17.0% [95% CI: -4.0; 33.7%]). Protein expression of proteins involved in mitochondrial capacity in skeletal muscle and glucose uptake were most improved with HIIT + walking, and no significant effects were observed with walking alone.

CONCLUSIONS

Twelve weeks of low-volume HIIT training can improve glucose control and induces adaptations in skeletal muscle important for metabolic health in individuals with prediabetes.

Effects of practical models of low-volume high-intensity interval training on glycemic control and insulin resistance in adults: a systematic review and meta-analysis of randomized controlled studies

Objectives

The aim of this systematic review and meta-analysis was to investigate the effects of practical models of low-volume high-intensity interval training protocols (LV-HIIT) on glucose control and insulin resistance compared with moderate-intensity continuous training (MICT) protocols and no-exercise controls (CON).

Methods

Four databases (PubMed, Web of Science, Scopus, and Cochrane Library) were searched for randomized controlled studies conducted using LV-HIIT interventions (HIIT/SIT protocols involving ≤ 15 min of intense training, within a session lasting ≤ 30 min; < 30 s all-out sprint for SIT additionally). The inclusion criteria required glucose and insulin resistance markers to be evaluated pre- and post-intervention among adults who were not trained athletes.

Results

As a result, twenty studies were included, and meta-analyses were conducted using sixteen studies employing HIIT protocols. Compared with CON, LV-HIIT with reduced intensity and extended interval duration significantly improved fasting glucose (FPG) (mean difference (MD) in mg/dL=-16.63; 95% confidence interval (CI): -25.30 to -7.96; p<0.001) and HbA1c (MD=-0.70; 95% CI: -1.10 to -0.29; p<0.001). Greater improvements were found in participants who were overweight/obese or having type 2 diabetes (T2D). FPG decreased with every additional second of interval duration (β;=-0.10; 95% CI: -0.19 to -0.00; p=0.046). FPI (β;=-0.65; 95% CI: -1.27 to -0.02; p=0.042) and HOMA-IR (β;=-0.22; 95% CI: -0.36 to -0.09; p=0.001) decreased with every additional minute of interval duration per session. HOMA-IR also decreased with every additional minute of weekly interval duration (β;=-0.06; 95%CI: -0.08 to -0.04; p<0.001). Compared with MICT, LV-HIIT was more effective in improving insulin sensitivity (SMD=-0.40; 95%CI: -0.70 to -0.09; p=0.01), but there were no differences in FPG, FPI, HbA1c or HOMA-IR (p>0.05). The effect of LV-HIIT on FPI was larger compared with MICT among individuals who lost weight.

Conclusion

Conclusively, a practical model of LV-HIIT with reduced intensity and extended interval was effective in improving glucose control and its effects were similar to MICT. Greater improvements were found in individuals with overweight/obesity or T2D in protocols with longer intervals or accumulated interval duration per session/week. More large-scale, randomized controlled studies with similar intervention protocols in a wide range of population are warranted to confirm these important results.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42024516594.

History and perspectives on interval training in sport, health, and disease

Exercise can be conducted as low-intensity continuous training (LICT) or a variety of higher intensity work/rest formats, collectively called interval training. Interval training was developed for athletes in the early 20th century. It was systemized in Sweden as Fartlek, and in Germany as die interval Method, in the 1930s. Most contemporary forms of interval training evolved from these progenitors. In essence, interval training allows a large volume of high-intensity or race specific training to be performed while controlling the development of fatigue. Adding interval training to LICT done by athletes adds about 2%-4% to performance achievable with LICT, which represents a competitively meaningful difference in performance (e.g., 4:25 vs. 4:00 over 1 mile). More recently, interval training has been applied to health- fitness participants and even to patients with health conditions. Studies indicate that a comparatively low volume of interval training can produce substantial improvement in physiologic capacity, in as little as 20% of training time versus LICT. There are data indicating that interval training can be reasonably pleasant, have good adherence, and is safe, even in patients. Although interval training was originally designed for athletics, the fundamental patterns of work versus recovery are remarkably similar in healthy adults and patients. Although the total volume of training and both absolute and relative intensity and magnitude of homeostatic disturbance are larger in athletes, the overall pattern of effort is the same in fitness participants and patients. Interval training can thus be characterized as an important step in the evolution of exercise training.

An acute bout of 4 × 4-min or 10 × 1-min HIIT improves β cell glucose sensitivity in postmenopausal females with type 2 diabetes: a secondary analysis

Improvements in glycemic control following acute exercise are typically attributed to improved postexercise insulin sensitivity (IS) with comparatively little known about how acute exercise impacts β cell function, especially in postmenopausal females. We determined how two high-intensity interval training (HIIT) protocols, matched for total estimated energy expenditure, impact β cell function in postmenopausal females with type 2 diabetes. Thirteen postmenopausal females (70 ± 5 yr; 12 ± 7 yr since diagnosis, 80.9 ± 13.8 kg, 32.4 ± 5.6 kg·m2; HbA1c-49.8 ± 10.3 mmol/mol [6.7 ± 1.0]) living with type 2 diabetes were included in this semirandomized crossover trial. The trial involved an initial resting control condition followed by two HIIT conditions [4 × 4-min HIIT (HIIT4) and 10 × 1-min HIIT (HIIT10)] completed in a randomized order 2-4 days apart. β cell function (glucose sensitivity) and insulin sensitivity were determined from a 2-h mixed-meal tolerance test performed 2 h after rest or HIIT. Both HIIT4 and HIIT10 significantly improved β cell glucose sensitivity compared with control (15 pmol/min/m2/[mmol/L], [95% confidence interval (CI) 6, 23]; P = 0.002 and 16 pmol/min/m2/[mmol/L], [95% CI 7, 25]; P = 0.002, respectively), with no difference between HIIT protocols (1 [-8, 10], P = 0.79). There were no significant differences in IS metrics (Matsuda index, OGIS, Stumvoli, and QUICKI) between the conditions. An acute bout of 4 × 4-min or 10 × 1-min HIIT improves β cell glucose sensitivity in postmenopausal females living with type 2 diabetes. ClinicalTrials.gov: NCT04986345.NEW & NOTEWORTHY This is the first study to explore the effects of acute high-intensity interval training (HIIT) on β cell function in postmenopausal women with type 2 diabetes. Our crossover trial compares two HIIT protocols, matched for total estimated energy expenditure, examining their impacts on β cell function and insulin sensitivity. Despite the absence of an insulin-sensitizing effect, we show robust effects of HIIT on β-cell function, including an improvement in β-cell glucose sensitivity.

Protein Supplementation Increases Adaptations to Low-Volume, Intra-Session Concurrent Training in Untrained Healthy Adults: A Double-Blind, Placebo-Controlled, Randomized Trial

Combined endurance and resistance training, also known as "concurrent training", is a common practice in exercise routines. While concurrent training offers the benefit of targeting both cardiovascular and muscular fitness, it imposes greater physiological demands on the body compared to performing each modality in isolation. Increased protein consumption has been suggested to support adaptations to concurrent training. However, the impact of protein supplementation on responses to low-volume concurrent training is still unclear. Forty-four untrained, healthy individuals (27 ± 6 years) performed two sessions/week of low-volume high-intensity interval training on cycle ergometers followed by five machine-based resistance training exercises for 8 weeks. Volunteers randomly received (double-blinded) 40 g of whey-based protein (PRO group) or an isocaloric placebo (maltodextrin, PLA group) after each session. Maximal oxygen consumption (VO2max) and overall fitness scores (computed from volunteers' VO2max and one-repetition maximum scores, 1-RM) significantly increased in both groups. The PRO group showed significantly improved 1-RM in all major muscle groups, while the PLA group only improved 1-RM in chest and upper back muscles. Improvements in 1-RM in leg muscles were significantly greater in the PRO group versus the PLA group. In conclusion, our results indicate that adaptations to low-volume concurrent training, particularly leg muscle strength, can be improved with targeted post-exercise protein supplementation in untrained healthy individuals.

Can Neuromuscular Electrical Stimulation Enhance the Effect of Sprint Interval Training?

The aim of this study was to determine the effects of subtetanic neuromuscular electrical stimulation combined with voluntary exercise between repeated Wingate tests on sprint exercise performance and blood lactate accumulation during sprint interval training. Fifteen healthy young males volunteered. After 1-min baseline, participants underwent the Wingate test twice. They performed a 4-min intervention between tests: neuromuscular electrical stimulation with free-weight cycling or voluntary cycling alone [43.6 (8.0) watts], which matched oxygen consumption with neuromuscular electrical stimulation with free-weight cycling. The blood lactate concentration was assessed at the end of the baseline, at 3-min intervention, and on recovery at 1, 3, 5, and 10 min after the second Wingate test. Peak and mean blood lactate concentration during recovery were significantly greater with neuromuscular electrical stimulation with free-weight cycling than voluntary cycling alone (P>0.036 and P=0.011, respectively). Peak power, mean power, and rate of decline (fatigue index) were not significantly different between conditions in both Wingate tests (condition/interaction all P>0.300, partial η2<0.1). Subtetanic neuromuscular electrical stimulation combined with voluntary exercise indicated similar exercise performance and fatigue levels during Wingate tests, but enhanced blood lactate accumulation compared to oxygen consumption-matched voluntary cycling during sprint interval training.

Effect of high-intensity interval training vs. moderate-intensity continuous training on cardiometabolic risk factors in overweight and obese individuals

OBJECTIVES

Our study aims to compare the effects of an 8-week high-intensity interval training (HIIT) vs. moderate-intensity continuous training (MICT) on cardiometabolic risk factors and on serum leptin levels in overweight and obese individuals.

METHODS

Our quasi-experimental study involved 36 students who were assigned to HIIT, MICT or the control group. Using a bicycle ergometer, participants in the HIIT group performed 25 min of HIIT and those in the MICT group performed 35 min of moderate-intensity continuous exercise for three days a week for 8 weeks. Body composition estimated by bioimpedance analysis, blood lipids and serum leptin were measured pre-exercise and 8 weeks post-exercise.

RESULTS

After 8 weeks of exercise, the participants in the MICT group showed a significant reduction in weight (p<0.01) and body mass index (BMI) (p<0.05). In the HIIT group, although weight reduction was noticed, the difference was not statistically significant compared to the pre-exercise values. In the control group, participants had a significant increase in their weight, BMI, and total body fat (p<0.05). On performing an inter-group comparison of the magnitude of change in body weight and BMI over 8 weeks of exercise, no difference was seen between the HIIT and MICT groups. No difference was observed in body fat indices and levels of random blood glucose, blood lipids and serum leptin pre and 8 weeks post-exercise.

CONCLUSIONS

On comparing the change in body weight and BMI over 8 weeks, no significant difference was found between the HIIT and MICT groups. However, HIIT was notably more time efficient.

Reduced-exertion high-intensity interval training (REHIT): a feasible approach for improving health and fitness?

In recent years, research investigating the dose-response to sprint interval training (SIT) has provided evidence that the number and duration of repetitions in a SIT session can be reduced whilst preserving the beneficial health-related adaptations. Together this research has led to the development of protocols involving minimal doses of SIT: regularly performing just two or three 20-30 s all-out sprints in a 10 min training session has been shown to elicit beneficial metabolic and cardiovascular adaptations. These SIT protocols, which we originally termed "reduced-exertion high-intensity interval training" (or REHIT), have the potential to remove many of the common barriers associated with other SIT protocols, as well as with HIT and aerobic exercise. Here, we critically review the evidence on the efficacy, feasibility and acceptability, and effectiveness of REHIT for improving health and fitness.

Applicability of a supramaximal high-intensity interval training program for older adults previously not engaged in regular exercise; analyses of secondary outcomes from the Umeå HIT Study

This analysis of secondary outcomes investigated the applicability of supramaximal high-intensity interval training (HIT) with individually prescribed external intensity performed on stationary bicycles. Sixty-eight participants with a median (min; max) age of 69 (66; 79), at the time not engaged in regular exercise were randomized to 25 twice-weekly sessions of supramaximal HIT (20-min session with 10 × 6-s intervals) or moderate-intensity training (MIT, 40-min session with 3 × 8-min intervals). The primary aim was outcomes on applicability regarding; adherence to prescribed external interval intensity, participant reported positive and negative events, ratings of perceived exertion (RPE 6-20), and affective state (Feeling Scale, FS -5-5). A secondary aim was to investigate change in exercise-related self-efficacy (Exercise Self-Efficacy Scale) and motivation (Behavioural Regulations in Exercise Questionnaire-2). Total adherence to the prescribed external interval intensity was [median (min; max)] 89 % (56; 100 %) in supramaximal HIT, and 100 % (95; 100 %) in MIT. The supramaximal HIT group reported 60 % of the positive (112 of 186) and 36 % of the negative (52 of 146) events. At the end of the training period, the median (min; max) session RPE was 15 (12; 17) for supramaximal HIT and 14 (9; 15) for MIT. As for FS, the median last within-session rating was 3 (-1; 5) for supramaximal HIT and 3 (1; 5) for MIT. Exercise-related motivation increased (mean difference in Relative Autonomy Index score = 1.54, 95 % CI [0.69; 2.40]), while self-efficacy did not change (mean difference = 0.55, 95 % CI [-0.75; 1.82]), regardless of group. This study provide support for supramaximal HIT in supervised group settings for older adults.

A single all-out bout of 30-s sprint-cycle performed on 5 consecutive days per week over 6 weeks does not enhance cardiovascular fitness, maximal strength, and clinical health markers in physically active young adults

BACKGROUND

This study examined the effects of a single all-out bout of 30-s sprint-cycle performed daily for 5 consecutive days per week for 6 weeks, on aerobic fitness, muscle strength and metabolic-health markers in physically active young males and females.

METHODS

Healthy, physically active 20-28 year olds, were randomly assigned to either experimental (EXP, N = 11) or non-training control (CON, N = 8) group. With supervision, the EXP group performed one bout of 30-s sprint-cycle daily, Mondays to Fridays over 6 weeks, while CON group continued with their usual lifestyle. The followings were measured at pre- and post-intervention: maximal aerobic power, peak torque of knee extensors and flexors at velocities 30° s-1 and 300° s-1, resting heart rate, resting blood pressure, body fat percentage, fasting lipid profile, fasting blood glucose, and fasting insulin levels.

RESULTS

There were no significant improvements in the EXP group for all the measured variables (all P > 0.05); except for significant interaction effects in peak torque of knee extensors at 30° s-1 (P = 0.044) and low-density lipoprotein-cholesterol (P = 0.046). Post hoc test indicate that CON group showed decline in their low-density lipo-proteins levels (P = 0.024).

CONCLUSION

Six weeks of one all-out bout of 30-s sprint-cycle per day, for 5 consecutive days per week, was ineffective in improving cardiovascular fitness, maximal strength, and most health markers in physically active young adults. The present results when combined with the previous literature suggest that there is a possibility of a minimum threshold for a number of sprint-cycle bouts needed to be performed before any form of cardio-metabolic-health benefit is accrued.

No Sex Differences in Perceptual Responses to High-Intensity Interval Training or Sprint Interval Training

ABSTRACT

Coe, LN and Astorino, TA. No sex differences in perceptual responses to high-intensity interval training or sprint interval training. J Strength Cond Res 36(6): 1025-1032, 2024-High-intensity interval training (HIIT) elicits similar and, in some cases, superior benefits vs. moderate-intensity continuous training (MICT). However, HIIT is typically more aversive than MICT because of the higher intensity and in turn, greater blood lactate accumulation (BLa). This study explored potential sex differences in perceptual responses to acute HIIT and sprint interval training. Fifteen men (age and V̇O2max = 29 ± 8 years and 39 ± 3 ml·kg-1·min-1) and 13 women (age and V̇O2max = 22 ± 2 years and 38 ± 5 ml·kg-1·min-1) who are healthy and recreationally active initially underwent testing of maximal oxygen uptake (V̇O2max) on a cycle ergometer. In randomized order on 3 separate occasions, they performed the 10 × 1-minute protocol at 85% of peak power output, 4 × 4-minute protocol at 85-95% maximal heart rate (%HRmax), or reduced exertion high intensity interval training consisting of 2 "all-out" 20-second sprints at a load equal to 5% body mass. Before and throughout each protocol, rating of perceived exertion (rating of perceived exertion [RPE] 6-20 scale), affective valence (+5 to -5 of the Feeling Scale), and BLa were assessed. Five minutes postexercise, enjoyment was measured using the Physical Activity Enjoyment scale survey. Results showed no difference in RPE (p = 0.17), affective valence (0.27), or enjoyment (p = 0.52) between men and women. Blood lactate accumulation increased in response to all protocols (p < 0.001), and men showed higher BLa than women (p = 0.03). Previous research suggests that interval exercise protocols are not interchangeable between men and women, yet our data reveal that men and women having similar V̇O2max exhibit no differences in perceptual responses to interval exercise.

Cardiorespiratory and Neuromuscular Improvements Plateau after 2 wk of Sprint Interval Training in Sedentary Individuals

INTRODUCTION

Previous studies ranging from 2 to 12 wk of sprint interval training (SIT) have reported improvements in maximal oxygen uptake (V̇O 2max ) and neuromuscular function in sedentary populations. However, whether the time course of the changes in these variables correlates with greater training volumes is unclear.

METHODS

Thirteen sedentary participants performed three all-out training weekly sessions involving 15-s sprints interspersed with 2 min of recovery on a cycle ergometer. The 6-wk training program was composed of three identical blocks of 2 wk in which training volume was increased from 10 to 14 repetitions over the first four sessions and reduced to 8 in the last session. The power output and the heart rate (HR) were monitored during the sessions. The V̇O 2max , the power-force-velocity profile, and the isometric force were assessed every 2 wk from baseline.

RESULTS

A significant increase in V̇O 2max was observed from the second week plateauing thereafter despite four additional weeks of training. The dynamic force production increased from the second week, and the speed production decreased by the end of the protocol. The isometric force and the maximal power output from the power-force-velocity profile did not change. Importantly, the time spent at high percentages of the maximal HR during the training sessions was lower in the second and third training block compared with the first.

CONCLUSIONS

SIT resulted in an effective approach for rapidly increasing V̇O 2max , and no change in the isometric force was found; cycling-specific neuromuscular adaptations were observed from the second week of training. SIT may be useful in the short term, but further improvement of overall physical fitness might need other training modalities like endurance and/or resistance training.

When Studying Affective Responses to Exercise, the Definition of "Intensity" Must Reference Homeostatic Perturbations: A Retort to Vollaard et al

In articles on the methodology of studies investigating affective and enjoyment responses to high-intensity interval training, we noted that, occasionally, exercise conditions described as involving "high" intensity exhibited heart rates that were only as high as, or even lower than, heart rates recorded during comparator conditions described as being of "moderate" intensity. Drs. Vollaard, Metcalfe, Kinghorn, Jung, and Little suggest instead that exercise intensity in high-intensity interval-training studies can be defined in terms of percentages of peak workload. Although we maintain that defining exercise intensity in terms of percentages of maximal heart rate is a suboptimal way to quantify the degree of homeostatic perturbations in response to exercise, we are unconvinced that definitions of intensity relying solely on workload are appropriate for studies investigating affective and enjoyment responses to exercise. The reason is that affect is theorized to have evolved to relay information about homeostatic perturbations to consciousness.

Effect of high-intensity interval training and moderate-intensity continuous training on cardiovascular risk factors in adolescents: Systematic review and meta-analysis of randomized controlled trials

BACKGROUND

In recent years, cardiovascular diseases in adolescents have become more serious. High intensity interval training (HIIT) and moderate intensity continuous training (MICT) have been shown to improve cardiovascular diseases in adolescents. Meta-analysis was conducted to compare the effects of HIIT and MICT on cardiovascular risk factors in adolescents.

METHODS

Randomised controlled trials of HIIT and MICT for cardiovascular risk factors in adolescents up to January 2023 were searched using authoritative databases such as CNKI, Web of Science, PubMed, and EBSCO. Data analysis was performed using Review Manage 5.4 and Stata 14.0.

RESULTS

A total of 12 studies involving 468 participants, mean age 15.19±4.35, were included in the study. The findings showed that compared with MICT, HIIT reduced adolescents' body weight (SMD=-0.18, 95 %CI=-0.58, 0.21) and increased maximal oxygen uptake (SMD=0.56, 95 %CI=0.20, 0.93) and high-density lipoprotein (SMD=-0.47, 95 % CI=-1.11, 0.17), and improved systolic blood pressure (SMD=-0.35, 95 %CI=-0.78, 0.09), glucose (SMD=-1.53, 95 %CI=-2.93, -0.13), and insulin (SMD=-0.66, 95 % CI=-1.73, 0.41), p<0.05. HIIT and MICT improved BMI, fat mass, diastolic blood pressure, triglycerides, total cholesterol, and LDL, with no significant difference between these training types.

CONCLUSION

HIIT was better than MICT for improving cardiovascular health in adolescents, with better effects on body weight, BMI, fat mass, systolic blood pressure, diastolic blood pressure, maximal oxygen uptake, triglyceride, total cholesterol, LDL, HDL, glucose, and insulin levels.

Is low-volume high-intensity interval training a time-efficient strategy to improve cardiometabolic health and body composition? A meta-analysis

The present meta-analysis aimed to assess the effects of low-volume high-intensity interval training (LV-HIIT; i.e., ≤5 min high-intensity exercise within a ≤15 min session) on cardiometabolic health and body composition. A systematic search was performed in accordance with PRISMA guidelines to assess the effect of LV-HIIT on cardiometabolic health and body composition. Twenty-one studies (moderate to high quality) with a total of 849 participants were included in this meta-analysis. LV-HIIT increased cardiorespiratory fitness (CRF, SMD = 1.19 [0.87, 1.50]) while lowering systolic blood pressure (SMD = -1.44 [-1.68, -1.20]), diastolic blood pressure (SMD = -1.51 [-1.75, -1.27]), mean arterial pressure (SMD = -1.55 [-1.80, -1.30]), MetS z-score (SMD = -0.76 [-1.02, -0.49]), fat mass (kg) (SMD = -0.22 [-0.44, 0.00]), fat mass (%) (SMD = -0.22 [-0.41, -0.02]), and waist circumference (SMD = -0.53 [-0.75, -0.31]) compared to untrained control (CONTROL). Despite a total time-commitment of LV-HIIT of only 14%-47% and 45%-94% compared to moderate-intensity continuous training and HV-HIIT, respectively, there were no statistically significant differences observed for any outcomes in comparisons between LV-HIIT and moderate-intensity continuous training (MICT) or high-volume HIIT. Significant inverse dose-responses were observed between the change in CRF with LV-HIIT and sprint repetitions (β = -0.52 [-0.76, -0.28]), high-intensity duration (β = -0.21 [-0.39, -0.02]), and total duration (β = -0.19 [-0.36, -0.02]), while higher intensity significantly improved CRF gains. LV-HIIT can improve cardiometabolic health and body composition and represent a time-efficient alternative to MICT and HV-HIIT. Performing LV-HIIT at a higher intensity drives higher CRF gains. More repetitions, longer time at high intensity, and total session duration did not augment gains in CRF.

Excess post-exercise oxygen consumption after reduced exertion high-intensity interval training on the cycle ergometer and rowing ergometer

PURPOSE

To examine differences in oxygen consumption ([Formula: see text]O2), ventilation ([Formula: see text]E), excess post-exercise oxygen consumption (EPOC), energy expenditure (EE), and blood lactate concentration (BLa) between reduced exertion high-intensity interval training (REHIT) performed on the cycle- and rowing ergometer.

METHODS

Fourteen active participants (age = 27 ± 7 yr) initially completed two assessments of maximal oxygen uptake. On two subsequent days, participants completed REHIT requiring three 20 s "all-out" sprints on the cycle-(REHIT-CE) and rowing ergometer (REHIT-RE), followed by 60 min rest during which gas exchange data and BLa were measured.

RESULTS

During exercise, [Formula: see text]O2 increased significantly in response to REHIT-CE (0.21 ± 0.04 L/min vs. 1.34 ± 0.37 L/min, p < 0.001) and REHIT-RE (0.23 ± 0.05 L/min vs. 1.57 ± 0.47 L/min, p < 0.001) compared to rest, and [Formula: see text]O2 remained elevated at 15, 30, and 45 min post-exercise in REHIT-CE (p < 0.001). However, [Formula: see text]O2 was only elevated 15 min after REHIT-RE (0.23 ± 0.05 L/min vs. 0.40 ± 0.11 L/min, p < 0.001). [Formula: see text]O2 (1.57 ± 0.47 L/min vs. 1.34 ± 0.37 L/min, p = 0.003) and EE (94.98 ± 29.60 kcal vs. 82.05 ± 22.85 kcal, p < 0.001) were significantly greater during REHIT-RE versus REHIT-CE. EPOC was significantly greater after REHIT-CE versus REHIT-RE (6.69 ± 2.18 L vs. 5.52 ± 1.67 L, p = 0.009). BLa was ~ twofold higher in response to REHIT-CE vs. REHIT-RE (11.11 ± 2.43 vs. 7.0 ± 2.4, p < 0.001).

CONCLUSION

Rowing-based REHIT elicits greater oxygen consumption and EE during exercise, yet lower EPOC and BLa. Whether rowing-based REHIT augments reductions in fat loss remains to be determined.

Changes of Anaerobic Power and Lactate Concentration following Intense Glycolytic Efforts in Elite and Sub-Elite 400-meter Sprinters

400-m races are based on anaerobic energy metabolism, they induce significant muscle fatigue, muscle fiber damage, and high blood lactate (LA) concentration. Despite extensive research on sprint training, our understanding of the training process that leads to world-class sprint performance is rather limited. This study aimed to determine differences in LA concentration and anaerobic power using jumping tests after an intense glycolytic effort in a group of elite and sub-elite 400-m runners. One hundred thirty male runners were divided into two groups: elite (n = 66, body mass = 73.4 ± 7.8 kg, body height = 182.1 ± 6.2 cm, age = 20.8 ± 4.0 y) running the 400-m dash below 50 s and sub-elite (n = 64, body mass = 72.0 ± 7.1 kg, body height = 182.1 ± 5.2 cm, age = 20.8 ± 4.0 y) with a 400-m personal best above 50 s. The power of the countermovement and the sequential squat jumps was measured in two sets after a warm-up, followed by two intermittent 30-s Wingate tests. LA concentration was measured eight times. It was observed that elite athletes achieved significantly higher power in both types of jumps. The maximum post-exercise LA concentration was significantly lower in the sub-elite group after the 3rd, the 6th, the 9th, and the 20th min after the cessation of two Wingate tests (p < 0.001). The rate of LA accumulation after exercise and the rate of LA utilization did not differ between the groups. It can be concluded that elite and non-elite runners differ in higher LA production but not in LA utilization. Anaerobic power and LA concentration seem to differentiate between 400 elite and sub-elite performance.

Cardiorespiratory Fitness and Performance Adaptations to High-Intensity Interval Training: Are There Differences Between Men and Women? A Systematic Review with Meta-Analyses

BACKGROUND

It is important to consider biological sex as a variable that might influence exercise adaptation in order to optimize exercise prescription for men and women.

OBJECTIVE

The aim of this study was to quantify the impact of biological sex on maximal oxygen uptake ([Formula: see text]O2max) and performance outcomes after high-intensity interval training (HIIT).

METHODS

A systematic search and review was conducted by two independent reviewers up to 8 September 2022 using MEDLINE, SPORTDiscus, and Sports Medicine & Education Index in ProQuest. Trials including healthy adults were included if they presented data for or compared male and female [Formula: see text]O2max or performance outcomes in response to HIIT. Performance outcomes included measures of exercise performance and concurrently measured physiological adaptations. Where appropriate, a random-effects, pre-post meta-analysis was undertaken. Data were sub-grouped for men and women, baseline training level, mean age, intervention type, and intervention length. Heterogeneity was assessed using Chi2, Cochran's Q, and Higgins I2 and sensitivity analyses, where required. Study quality was assessed using the Newcastle-Ottawa Scale and publication bias was assessed through visual inspection of funnel plots.

RESULTS

Thirty-three references from 28 trials were included in the review (n = 965; 462 women and 503 men). Meta-analyses included 19 studies for [Formula: see text]O2max, eight for peak power output from [Formula: see text]O2max testing (PPO), and five for threshold power (powerAT). Meta-analyses revealed similar increases in [Formula: see text]O2max in women (g = 0.57; 95% CI 0.44-0.69) and men (g = 0.57; 95% CI 0.42-0.72), and powerAT in women (g = 0.38; 95% CI 0.13-0.64) and men (g = 0.38; 95% CI 0.11-0.64). Raw mean differences for change in [Formula: see text]O2max were Δ 0.32 L·min-1 and 3.50 mL·kg-1·min-1 in men, versus Δ 0.20 L·min-1 and 3.34 mL·kg-1·min-1 for women. No significant sex differences were present for the primary analysis of any outcome. After sub-grouping, significant differences were present for PPO where the effect size was higher for well-trained women (g = 0.37) compared with well-trained men (g = 0.17), and for [Formula: see text]O2max where interventions with a duration of 4 weeks or less had significantly smaller effect sizes compared with those longer than 4 weeks (p < 0.001). Unweighted mean percentage change in [Formula: see text]O2max, PPO, and powerAT across studies was 11.16 ± 7.39%, 11.16 ± 5.99%, and 8.07 ± 6.55% for women, and 10.90 ± 5.75%, 8.22 ± 5.09%, and 7.09 ± 7.17% for men, respectively. Significant heterogeneity was present for both [Formula: see text]O2max and PPO (I2, range: 62.06-78.80%). Sub-grouping by baseline training status and intervention length decreased heterogeneity in most groups. A qualitative synthesis of other outcomes indicated similar improvements in fitness and performance for men and women with some evidence suggesting differences in the mechanisms of adaptation.

LIMITATIONS AND RISK OF BIAS

Publication bias is unlikely to have significantly influenced results for [Formula: see text]O2max or powerAT, but the meta-analysis of PPO could have benefitted from additional study data to strengthen results. The overlap in age categories and sensitivity of the analysis limits the accuracy of the results of the sub-grouping by age.

CONCLUSIONS

Findings indicated no sex-specific differences for any fitness or performance outcomes. Baseline training status and intervention length accounted for most variability in outcomes. PROSPERO registration number: CRD42021272615.

Biological sex does not influence the peak cardiac output response to twelve weeks of sprint interval training

Sprint interval training (SIT) increases peak oxygen uptake (V̇O2peak) but the mechanistic basis is unclear. We have reported that 12 wk of SIT increased V̇O2peak and peak cardiac output (Q̇peak) and the changes in these variables were correlated. An exploratory analysis suggested that Q̇peak increased in males but not females. The present study incorporated best practices to examine the potential influence of biological sex on the Q̇peak response to SIT. Male and female participants (n = 10 each; 21 ± 4 y) performed 33 ± 2 sessions of SIT over 12 wk. Each 10-min session involved 3 × 20-s 'all-out' sprints on an ergometer. V̇O2peak increased after SIT (3.16 ± 1.0 vs. 2.89 ± 1.0 L/min, η2p = 0.53, p < 0.001) with no sex × time interaction (p = 0.61). Q̇peak was unchanged after training (15.2 ± 3.3 vs. 15.1 ± 3.0 L/min, p = 0.85), in contrast to our previous study. The peak estimated arteriovenous oxygen difference increased after training (204 ± 30 vs. 187 ± 36 ml/L, p = 0.006). There was no effect of training or sex on measures of endothelial function. We conclude that 12 wk of SIT increases V̇O2peak but the mechanistic basis remains unclear. The capacity of inert gas rebreathing to assess changes in Q̇peak may be limited and invasive studies that use more direct measures are needed.

Rates of compliance and adherence to high-intensity interval training: a systematic review and Meta-analyses

BACKGROUND

To determine rates of compliance (i.e., supervised intervention attendance) and adherence (i.e., unsupervised physical activity completion) to high-intensity interval training (HIIT) among insufficiently active adults and adults with a medical condition, and determine whether compliance and adherence rates were different between HIIT and moderate-intensity continuous training (MICT).

METHODS

Articles on adults in a HIIT intervention and who were either insufficiently active or had a medical condition were included. MEDLINE, EMBASE, PsychINFO, SPORTDiscus, CINAHL, and Web of Science were searched. Article screening and data extraction were completed by two independent reviewers. Risk of bias was assessed using RoB 2.0 or ROBINS-I. Meta-analyses were conducted to discern differences in compliance and adherence between HIIT vs. MICT. Sensitivity analyses, publication bias, sub-group analyses, and quality appraisal were conducted for each meta-analysis.

RESULTS

One hundred eighty-eight unique studies were included (n = 8928 participants). Compliance to HIIT interventions averaged 89.4% (SD:11.8%), while adherence to HIIT averaged 63% (SD: 21.1%). Compliance and adherence to MICT averaged 92.5% (SD:10.6%) and 68.2% (SD:16.2%), respectively. Based on 65 studies included in the meta-analysis, compliance rates were not different between supervised HIIT and MICT interventions [Hedge's g = 0.015 (95%CI: - 0.088-0.118), p = .78]. Results were robust and low risk of publication bias was detected. No differences were detected based on sub-group analyses comparing medical conditions or risk of bias of studies. Quality of the evidence was rated as moderate over concerns in the directness of the evidence. Based on 10 studies, adherence rates were not different between unsupervised HIIT and MICT interventions [Hedge's g = - 0.313 (95%CI: - 0.681-0.056), p = .096]. Sub-group analysis points to differences in adherence rates dependent on the method of outcome measurement. Adherence results should be interpreted with caution due to very low quality of evidence.

CONCLUSIONS

Compliance to HIIT and MICT was high among insufficiently active adults and adults with a medical condition. Adherence to HIIT and MICT was relatively moderate, although there was high heterogeneity and very low quality of evidence. Further research should take into consideration exercise protocols employed, methods of outcome measurement, and measurement timepoints.

REGISTRATION

This review was registered in the PROSPERO database and given the identifier CRD42019103313.

Effects of the order of endurance and high-intensity interval exercise in combined training on mouse skeletal muscle metabolism

Endurance exercise (EE) mainly improves oxidative capacity, whereas high-intensity interval exercise (HIIE) also improves glycolytic capacity. There is growing evidence that suggests that combining EE with HIIE can lead to improved athletic performance and fitness outcomes compared with either form of exercise alone. This study aimed to elucidate whether the order in which EE and HIIE are performed in combined training affects oxidative metabolism and glycolysis in mouse skeletal muscle. Male ICR mice at 7 wk of age were divided into three groups: control (CON), EE-HIIE, and HIIE-EE. The total training period was 3 wk (3 times/week). Mice performed running on a treadmill as endurance exercise and swimming with a weight load of 10% of body weight as high-intensity interval exercise. EE before HIIE (EE-HIIE) improved running performance in the maximal EE capacity test (all-out test) and partly enhanced the expression levels of molecular signals involved in glycolysis compared with HIIE before EE (HIIE-EE). The order of exercise did not, however, impact the expression of proteins related to mitochondrial dynamics, including those involved in the morphological changes of mitochondria through repeated fusion and fission, as well as oxidative energy metabolism. The findings suggest that the order of exercise has no significant impact on the expression of proteins associated with glycolytic and oxidative energy metabolism. Nevertheless, our results indicate that the order of EE-HIIE may enhance running performance.

Is isoenergetic high-intensity interval exercise superior to moderate-intensity continuous exercise for cardiometabolic risk factors in individuals with type 2 diabetes mellitus? A single-blinded randomized controlled study

The aim of this study was to compare the effect of high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) with equal energy expenditure on glycaemic and cardiometabolic risk factors in people with Type 2 Diabetes Mellitus (T2DM) when compared to the control. Sixty-three people with T2DM were randomly assigned to HIIT, MICT, or non-exercising controls. Individuals were trained with HIIT at 90 and 30% of their VO2peak (1:2 min ratio) starting from 8 up to 16 intervals and MICT at 50% of VO2peak, on a cycle ergometer, 3 times/week for 12 weeks under supervision. The primary outcome measure was the change in HbA1c. Aerobic capacity, cardiovascular responses, anthropometric measures, body composition, glycaemic, and cardiometabolic risk factors were measured at the beginning and the end of the 12-week training period. There was no significant difference between HIIT and MICT or when compared to the control for HbA1c, glucose, insulin resistance, blood lipids, cardiovascular responses, anthropometric measures, body composition, and abdominal and visceral fat (padj > 0.05). HIIT and MICT increased VO2peak significantly compared to controls (p < 0.05) but not to each other (p > 0.05). Both HIIT and MICT improved VO2peak and HbA1c after 12 weeks of training compared to their baseline, furthermore, only MICT caused additional improvements in cardiovascular responses, anthropometric measures, and abdominal fat compared to baseline (p < 0.05). As a conclusion, isoenergetic HIIT or MICT did not improve HbA1c. The two protocols were equally efficient for improvement in aerobic capacity but had little effect on other cardiometabolic factors.Trial registration: ClinicalTrials.gov identifier: NCT03682445.HighlightsHIIT and MICT with equal energy expenditure were equally efficient for aerobic capacity compared to controls.Isoenergetic HIIT or MICT were not superior for improving HbA1c.Isoenergetic HIIT and MICT were not superior to each other for anthropometric measures, body composition, and cardiometabolic risk factors.

Neuromuscular and autonomic function is fully recovered within 24 h following a sprint interval training session

BACKGROUND

Recovery is a key factor to promote adaptations and enhance performance. Sprint Interval Training (SIT) is known to be an effective approach to improve overall physical function and health. Although a 2-day rest period is given between SIT sessions, the time-course of recovery after SIT is unknown.

PURPOSE

The aim of this study was to determine whether the neuromuscular and autonomic nervous systems would be impaired 24 and 48 h after an SIT session.

METHODS

Twenty-five healthy subjects performed an 8 × 15 s all-out session on a braked cycle ergometer with 2 min of rest between repetitions. Isometric maximal voluntary contraction (iMVC) and evoked forces to electrical nerve stimulation during iMVC and at rest were used to assess muscle contractile properties and voluntary activation before (Pre), 1 (Post24h), and 2 (Post48h) days after the session. Two maximal 7 s sprints with two different loads were performed at those same time-points to evaluate the maximal theoretical force (F0), velocity (V0) and maximal power (Pmax) production during a dynamic exercise. Additionally, nocturnal heart rate variability (HRV) was assessed the previous and the three subsequent nights to the exercise bout.

RESULTS

No significant impairments were observed for the iMVC or for the force evoked by electrical stimulation 1 day after the session. Similarly, F0, V0, and Pmax were unchanged at Post24h and Post48h. Furthermore, HRV did not reveal any temporal or frequential significant difference the nights following SIT compared to Pre.

CONCLUSION

The results of this study show a full recovery of neuromuscular and autonomic functions a day after an all-out SIT session.

Exploring interindividual differences in fasting and postprandial insulin sensitivity adaptations in response to sprint interval exercise training

Previous studies have concluded that wide variance in changes in insulin sensitivity markers following exercise training demonstrates heterogeneity in individual trainability. However, these studies frequently don't account for technical, biological, and random within-subject measurement error. We used the standard deviation of individual responses (SDIR) to determine whether interindividual variability in trainability exists for fasting and postprandial insulin sensitivity outcomes following low-volume sprint interval training (SIT). We pooled data from 63 untrained participants who completed 6 weeks of SIT (n = 49; VO2max: 35 (7) mL⋅kg-1⋅min-1) or acted as no-intervention controls (n = 14; VO2max: 34 (6) mL⋅kg-1⋅min-1). Fasting and oral glucose tolerance test (OGTT)-derived measures of insulin sensitivity were measured pre- and post-intervention. SDIR values were positive and exceeded a small effect size threshold for changes in fasting glucose (SDIR = 0.27 [95%CI 0.07,0.38] mmol⋅L-1), 2-h OGTT glucose (SDIR = 0.89 [0.22,1.23] mmol⋅L-1), glucose area-under-the-curve (SDIR = 66.4 [-81.5,124.3] mmol⋅L-1⋅120min-1) and The Cederholm Index (SDIR = 7.2 [-16.0,19.0] mg⋅l2⋅mmol-1⋅mU-1⋅min-1), suggesting meaningful individual responses to SIT, whilst SDIR values were negative for fasting insulin, fasting insulin resistance and insulin AUC. For all variables, the 95% CIs were wide and/or crossed zero, highlighting uncertainty about the existence of true interindividual differences in exercise trainability. Only 2-22% of participants could be classified as responders or non-responders with more than 95% certainty. Our findings demonstrate it cannot be assumed that variation in changes in insulin sensitivity following SIT is attributable to inherent differences in trainability, and reiterate the importance of accounting for technical, biological, and random error when examining heterogeneity in health-related training adaptations.Highlights This study tested whether true interindividual variability exists for changes in insulin sensitivity and glyceamic control following 6-weeks of low volume sprint interval training (SIT).The high level of technical, biological, and random error associated with repeated measurements of insulin sensitivity and glycaemic control, means we can neither confidently conclude that there is evidence of true interindividual differences in the trainability of these outcomes following SIT, nor confidently identify responders or non-responders for such parameters.Researchers contrasting responders vs. non-responders for a given parameter, either to understand mechanisms of adaptation and/or develop physiological/genetic/epigenetic predictors of response, need to be aware that identification of responders and non-responders with sufficient certainty may not be achievable for parameters with a high level of technical, biological, and random error.

Impaired Glucose Tolerance and Visceral Adipose Tissue Thickness among Lean and Non-Lean People with and without Spinal Cord Injury

After spinal cord injury (SCI), multiple adaptations occur that influence metabolic health and life quality. Prolonged sitting and inactivity predispose people with SCI to body composition changes, such as increased visceral adipose tissue (VAT) thickness, which is often associated with impaired glucose tolerance. Our goal is to understand whether VAT is an index of leanness, and, secondarily, whether mobility methods influence glucose tolerance for people living with SCI. A total of 15 people with SCI and 20 people without SCI had fasting oral glucose tolerance tests (OGTT) and VAT thickness (leanness) measured during a single session. Glucose was 51% and 67% greater for individuals with SCI relative to those without SCI after 60 and 120 min of an OGTT (p < 0.001). Glucose area under the curve (AUC) was 28%, 34%, and 60% higher for non-lean people with SCI than lean people with SCI and non-lean and lean people without SCI, respectively (p = 0.05, p = 0.009, p < 0.001). VAT was associated with glucose AUC (R2 = 0.23, p = 0.004). Taken together, these findings suggest that leanness, as estimated from VAT, may be an important consideration when developing rehabilitation programs to influence metabolism among people with SCI.

Long- and Short-Term High-Intensity Interval Training on Lipid Profile and Cardiovascular Disorders in Obese Male Adolescents

This study investigated the effects of short-term and long-term periods (8 and 16 weeks) of high-intensity interval training (HIIT) on cardiovascular components, blood lipids, and 6-min walking test performance in obese young boys (age = 16.2 ± 0.7) with >34% body fat. The participants were split into two groups: severe obesity (SOG; n = 17) and moderate obesity (MOG; n = 16). All participants performed on a cycle ergometer for 16 weeks (3 times per week) of HIIT at 100% peak power output at the ventilatory threshold and recovered at 50% of peak power. Except for BMI, both groups improved all body composition measures after 16 weeks, with a higher percentage of change (Δ) in SOG. The 6-min walking test increased in both groups (p < 0.001). Furthermore, cardiovascular variables, blood lactate concentration at rest and after 5-min post-exercise, blood lipids, and insulin concentrations improved significantly in both groups. After 16 weeks, MOG significantly improved in HR_peak, blood glucose concentration, and rating of perceived exertion (RPE), but the percentage of change (Δ) was higher in SOG for all the other variables. SOG showed a higher (Δ) waist-to-hip ratio, maximum heart rate, resting heart rate, systolic blood pressure, blood lactate at 5-min post-exercise, and triglyceride concentrations after 8 and 16 weeks of training. In conclusion, a long-term HIIT program appears to be an appropriate training approach for obese boys with extra body fat. However, considering the RPE values, short-duration training sessions should be planned.

When should I run-the role of exercise timing in metabolic health

The prevalence of type 2 diabetes is reaching epidemic proportions. First line therapy approaches are lifestyle interventions including exercise. Although a vast amount of studies reports on beneficial effects of exercise on metabolism in humans per se, overall data are contradictory which makes it difficult to optimize interventions. Innovative exercise strategies and its underlying mechanism are needed to elucidate in order to close this therapeutic gap. The skeletal muscle produces and secretes myokines and microRNAs in response to exercise and both are discussed as mechanisms linking exercise and metabolic adaptation. Aspects of chronophysiology such as diurnal variation in insulin sensitivity or exercise as a signal to reset dysregulated peripheral clocks are of growing interest in the context of impaired metabolism. Deep insight of how exercise timing determines metabolic adaptations is required to optimize exercise interventions. This review aims to summarize the current state of research on the interaction between timing of exercise and metabolism in humans, providing insights into proposed mechanistic concepts focusing on myokines and microRNAs. First evidence points to an impact of timing of exercise on health outcome, although data are inconclusive. Underlying mechanisms remain elusive. It is currently unknown if the timed release of mykokines depends on time of day when exercise is performed. microRNAs have been found as an important mediator of processes associated with exercise adaptation. Further research is needed to evaluate their full relevance. In conclusion, it seems to be too early to provide concrete recommendations on timing of exercise to maximize beneficial effects.

The Effects of Sprint Interval Training on Physical Performance: A Systematic Review and Meta-Analysis

ABSTRACT

Hall, AJ, Aspe, RR, Craig, TP, Kavaliauskas, M, Babraj, J, and Swinton, PA. The effects of sprint interval training on physical performance: a systematic review and meta-analysis. J Strength Cond Res 37(2): 457-481, 2023-The present study aimed to synthesize findings from published research and through meta-analysis quantify the effect of sprint interval training (SIT) and potential moderators on physical performance outcomes (categorized as aerobic, anaerobic, mixed aerobic-anaerobic, or muscular force) with healthy adults, in addition to assessing the methodological quality of included studies and the existence of small study effects. Fifty-five studies were included (50% moderate methodological quality, 42% low methodological quality), with 58% comprising an intervention duration of ≤4 weeks and an array of different training protocols. Bayesian's meta-analysis of standardized mean differences (SMD) identified a medium effect of improved physical performance with SIT (ES 0.5 = 0.52; 95% credible intervals [CrI]: 0.42-0.62). Moderator analyses identified overlap between outcome types with the largest effects estimated for anaerobic outcomes (ES 0.5 = 0.61; 95% CrI: 0.48-0.75). Moderator effects were identified for intervention duration, sprint length, and number of sprints performed per session, with larger effects obtained for greater values of each moderator. A substantive number of very large effect sizes (41 SMDs > 2) were identified with additional evidence of extensive small study effects. This meta-analysis demonstrates that short-term SIT interventions are effective for developing moderate improvements in physical performance outcomes. However, extensive small study effects, likely influenced by researchers analyzing many outcomes, suggest potential overestimation of reported effects. Future research should analyze fewer a priori selected outcomes and investigate models to progress SIT interventions for longer-term performance improvements.

Effect of aerobic exercise and low-carbohydrate high-fat diet on glucose tolerance and android/gynoid fat in overweight/obese women: A randomized controlled trial

The study was designed to compare the effects of weight loss induced by a low-carbohydrate-high-fat diet or a normal diet, with and without exercise, on glucose tolerance measured as area under the curve (AUC), and android (A) and gynoid (G) fat distribution. The study was registered at clinicaltrials.gov; NCT04100356. In total, 57 women classified as overweight or obese (age 40 ± 3.5 years, body mass index 31.1 ± 2.6 kg/m²) were randomly assigned and completed a 10-week intervention using a low-carbohydrate high-fat diet or a normal diet, with or without aerobic interval exercise. An equal deficit of 700 kcal/day was prescribed, either restricting the diet only, or moderately restricting diet and including three 50-min high-intensity bicycle sessions per week. There were thus four groups: normal diet (NORM); low-carbohydrate-high-fat diet (LCHF); normal diet with exercise (NORM-EX); and low-carbohydrate-high-fat diet with exercise (LCHF-EX). Linear mixed models was used to assess differences between groups. With all groups pooled, the intervention resulted in a weight loss of 6.7 ± 2.5% (p < 0.001). The intervention did not result in differences between groups in AUC glucose, nor in fasting glucose or indicis for insulin resistance such as Homeostatic Model Assessment, Matsuda Insulin Sensitivity Index, insulinogenic index and disposition index. Post-intervention android fat was lower in LCHF than NORM (3,223 ± 727 vs. 2,533 ± 535 g, p = 0.041). LCHF reached a lower A/G ratio than NORM (0.94 ± 0.12 vs. 1.04 ± 0.09, p = 0.011) and LCHF-EX (0.94 ± 0.12 vs. 1.09 ± 0.09, p < 0.001) after the intervention. LCHF resulted in lower android fat mass compared to NORM and the lowest A/G ratio compared to the other matched groups, but with no accompanying improvement in AUC glucose. In conclusion, although all groups achieved improvements in glucose tolerance, no superior effect was observed with the LCHF diet, neither with nor without exercise.

The effect of HIIT on body composition, cardiovascular fitness, psychological well-being, and executive function of overweight/obese female young adults

Purpose

To evaluate the effect of a short-term HIIT program on the selected health-related parameters for overweight/obese young adult women in a university context.

Methods

A total of 48 participants were randomly divided into two groups. The exercise group (HIIT) received a HIIT intervention of aerobics for 4 weeks, while the control group (CON) received no training. Body composition including waist circumference (WC), body fat percentage (BF %), Cardiorespiratory fitness (VO2max), the score of Self-Rating Depression Scale (SDS), and Stroop word-color test (SCWT) results were assessed before and after the intervention along with within- and between-group comparisons.

Results

All the indices were significantly improved in HIIT group (p < 0.01) after 4 weeks of intervention. No significant changes were found in CON. There were significant differences between HIIT and CON in cardiovascular fitness (p < 0.01), SDS (p < 0.01) and SCWT (p < 0.05) before and after 4 weeks. In addition, weekly measurements of HIIT effects showed significant changes (p < 0.01) from the second week in the variables of body composition, VO2max, SDS and SCWT when compared with the baseline and maintained the tendency till the end of program.

Conclusion

The short-term HIIT aerobics of the campus program conducted in a non-lab setting induced significant improvements in body composition, cardiovascular fitness, psychological well-being and executive function in overweight young female adults.

Effect of High-Intensity Interval Training on Functional Movement in Older Adults: A Systematic Review and Meta-analysis

BACKGROUND

Preserving physiological functional capacity (PFC), the ability to perform the activities of daily life, and the ease with which they can be performed, in older adults, defined for this study as ≥ 50 years of age, is an important consideration for maintaining health and independence through the ageing process. Physical activity, and exercise training in particular, has been positively associated with improvement in PFC. In addition to improving aerobic and anaerobic capacity, promoting and preserving functional movement as a component of PFC is an important goal of physical activity, especially for older adults. High-intensity interval training (HIIT), an exercise protocol where repeated bouts of increased intensity are interspersed with active or passive recovery periods, has often been studied as an alternative to traditional moderate-intensity continuous training (MICT) exercise, where a continuous intensity is maintained throughout the exercise session. A large body of research has determined that both types of exercise programme are effective in improving measures of aerobic and anaerobic fitness in older adults. However, the effect of the two exercise modalities on functional movement has most often been a secondary outcome, with a range of observational techniques applied for measurement.

OBJECTIVES

The primary objective of this research is to systematically review and meta-analyse published studies of HIIT interventions that measured functional movement in older adults to conclude if HIIT is effective for improving functional movement. A secondary objective is to determine if there are significant differences between HIIT and MICT effect on functional movement.

METHODS

A search strategy of terms locating studies of HIIT interventions, functional movement outcome measures, and older adult population samples was executed on seven digital databases. Randomized and pair-matched trials of > 2 weeks were considered for inclusion. Studies of participants with neurological impairment or studies using combined exercise modality were rejected. Standardized mean difference for functional movement outcome measures was calculated. A meta-analysis of the included studies and subgroups was performed along with study quality (risk of bias and publication bias) evaluation.

RESULTS

A total of 18 studies were included in random effects model pooled analysis. Subgroup analysis of HIIT versus MICT on functional movement showed a trivial effect in favour of HIIT (ES 0.13, 95% CI [-0.06, 0.33] p = 0.18) and did not achieve statistical significance. However, HIIT showed a medium, statistically significant favourable effect on functional movement versus non-intervention control (ES = 0.60 95% CI [0.24, 0.95] p = 0.001). Further subgroups analysis using singular and multiple functional movement outcome measures showed similar results.

CONCLUSION

This meta-analysis indicates that HIIT interventions in older adults may be effective at promoting improvements in functional movement, though it is unclear whether HIIT is superior to MICT.

Feasibility and outcomes of a real-world regional lung cancer prehabilitation programme in the UK

BACKGROUND

Prehabilitation, or multimodality patient optimisation before major treatment, has demonstrated meaningful improvements in patients' outcomes. In the setting of lung cancer surgery, postoperative complications and length of hospital stay are reduced, but there is currently limited access to prehabilitation. Prehab4Cancer (P4C) is an innovative regional programme serving all areas of Greater Manchester (GM).

METHODS

The lung cancer P4C service commenced in 2019 as a collaboration between the GM Cancer alliance and 12 leisure and community organisations. Patients planning surgical resection could be referred to receive exercise, nutrition, and well-being assessment and interventions before surgery. We evaluated the programme's feasibility, uptake, and outcomes during the 11 months before COVID-19 restrictions.

RESULTS

In total, 377 patients were referred to the lung cancer P4C service from all 11 hospitals in GM. Of the patients reached by telephone, 80.0% (n=280/348) attended initial P4C assessment, which occurred a median of 8 days (inter-quartile range [IQR]: 4-14) after referral. In addition, 74.3% (n=280/377) attended for baseline assessment and 47.7% (n=180/377) completed prehabilitation, attending a median of six sessions (IQR: 4-9). Statistically significant improvements in all objective physiological and subjective functional assessments were observed preoperatively, including a mean increase in the incremental shuttle walk test of 50 m (95% confidence interval: 25-74; P<0.001).

CONCLUSIONS

The P4C programme demonstrated feasibility at scale, high uptake, and promising impact on the status of patients with lung cancer before surgery. P4C is the first regional prehabilitation service internationally, and this evaluation provides a framework for implementing similar services in other regions.

Skeletal muscle mechanisms contributing to improved glycemic control following intense interval exercise and training

High-intensity and sprint interval training (HIIT and SIT, respectively) enhance insulin sensitivity and glycemic control in both healthy adults and those with cardiometabolic diseases. The beneficial effects of intense interval training on glycemic control include both improvements seen in the hours to days following a single session of HIIT/SIT and those which accrue with chronic training. Skeletal muscle is the largest site of insulin-stimulated glucose uptake and plays an integral role in the beneficial effects of exercise on glycemic control. Here we summarize the skeletal muscle responses that contribute to improved glycemic control during and following a single session of interval exercise and evaluate the relationship between skeletal muscle remodelling and improved insulin sensitivity following HIIT/SIT training interventions. Recent evidence suggests that targeting skeletal muscle mechanisms via nutritional interventions around exercise, particularly with carbohydrate manipulation, can enhance the acute glycemic benefits of HIIT. There is also some evidence of sex-based differences in the glycemic benefits of intense interval exercise, with blunted responses observed after training in females relative to males. Differences in skeletal muscle metabolism between males and females may contribute to sex differences in insulin sensitivity following HIIT/SIT, but well-controlled studies evaluating purported muscle mechanisms alongside measurement of insulin sensitivity are needed. Given the greater representation of males in muscle physiology literature, there is also a need for more research involving female-only cohorts to enhance our basic understanding of how intense interval training influences muscle insulin sensitivity in females across the lifespan.

High-Intensity Interval Training Versus Moderate-Intensity Continuous Training for Improving Physical Health in Elderly Women

In elderly women, a lack of regular physical exercise may result in faster decreases in general health and functional performance. Although high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) have been effectively applied in young and clinical groups, there is no evidence to support their use in elderly women to achieve health benefits. Thus, the major goal of this study was to investigate how HIIT affected health-related outcomes in elderly women. Twenty-four inactive elderly women agreed to participate in the 16-week HIIT and MICT intervention. Body composition, insulin resistance, blood lipids, functional capacity, cardiorespiratory fitness, and quality of life were all measured before and after the intervention. The number of differences between groups was determined using Cohen's effect sizes, and the pre-post intra-group changes were compared using paired t-tests. Using 2 × 2 ANOVA, the time × group interaction effects between HIIT and MICT were evaluated. Body fat percentage, sagittal abdominal diameter, waist circumference, and hip circumference all were improved significantly in the 2 groups. HIIT substantially improved fasting plasma glucose and cardiorespiratory fitness as compared to the MICT. HIIT improved the lipid profile and functional ability more significantly compared to the MICT group. These findings show that HIIT is a useful exercise for improving elderly women's physical health.

Effects of two workload-matched high intensity interval training protocols on regulatory factors associated with mitochondrial biogenesis in the soleus muscle of diabetic rats

Aims: High intensity interval training (HIIT) improves mitochondrial characteristics. This study compared the impact of two workload-matched high intensity interval training (HIIT) protocols with different work:recovery ratios on regulatory factors related to mitochondrial biogenesis in the soleus muscle of diabetic rats. Materials and methods: Twenty-four Wistar rats were randomly divided into four equal-sized groups: non-diabetic control, diabetic control (DC), diabetic with long recovery exercise [4-5 × 2-min running at 80%-90% of the maximum speed reached with 2-min of recovery at 40% of the maximum speed reached (DHIIT1:1)], and diabetic with short recovery exercise (5-6 × 2-min running at 80%-90% of the maximum speed reached with 1-min of recovery at 30% of the maximum speed reached [DHIIT2:1]). Both HIIT protocols were completed five times/week for 4 weeks while maintaining equal running distances in each session. Results: Gene and protein expressions of PGC-1α, p53, and citrate synthase of the muscles increased significantly following DHIIT1:1 and DHIIT2:1 compared to DC (p ˂ 0.05). Most parameters, except for PGC-1α protein (p = 0.597), were significantly higher in DHIIT2:1 than in DHIIT1:1 (p ˂ 0.05). Both DHIIT groups showed significant increases in maximum speed with larger increases in DHIIT2:1 compared with DHIIT1:1. Conclusion: Our findings indicate that both HIIT protocols can potently up-regulate gene and protein expression of PGC-1α, p53, and CS. However, DHIIT2:1 has superior effects compared with DHIIT1:1 in improving mitochondrial adaptive responses in diabetic rats.

Changes in the Fitness Fatness Index following reduced exertion high-intensity interval training versus moderate-intensity continuous training in physically inactive adults

Background

Many adults do not reach the recommended exercise participation guidelines, often citing lack of time as a barrier. Reduced exertion high-intensity training (REHIT) is a mode of exercise that takes as few as 10 min and has been shown to be as effective as other modalities. The Fitness Fatness Index (FFI) is a recently developed index that is used to predict cardiovascular disease (CVD) risk. The aim of this study was to determine the efficacy of a REHIT vs. a traditional moderate-intensity continuous training (MICT) on FFI in physically inactive adults.

Methods

Thirty-two participants were randomized into one of two 8-week exercise intervention groups: (i) REHIT (n = 16); (ii) MICT (n = 16). The REHIT group performed 10 min of individualized cycling intervals on 2–4 days of the week. The MICT group were prescribed aerobic exercise at 50–65% of their heart rate reserve (HRR) on 3–5 days of the week. FFI was recorded at baseline and post 8-weeks, with FFI being calculated as cardiorespiratory fitness (CRF) (expressed as metabolic equivalents) divided by waist to height ratio (WtHR). A 1-unit increase in FFI was recognized as a clinically significant change in FFI.

Results

The REHIT group showed significantly greater (+1.95, ±0.63) improvements in FFI compared to those in the MICT (+0.99, ±0.47) group (between group difference, p &lt; 0.001). Furthermore, there was a greater proportion of participants who achieved a clinically significant change in FFI in the REHIT group (12/12, 100%) than in the MICT group (8/15, 53%) (between group difference, p = 0.01).

Conclusion

This study suggests that REHIT may be a more efficacious exercise modality to increase FFI than MICT. This outcome is beneficial as the clinician can prescribe REHIT to physically inactive adults who cite lack of time as a barrier to physical activity participation and achieve significant reductions in CVD risk.

Skeletal Muscle Transcriptomic Comparison Between Men and Women in Response to Acute Sprint Exercise

Background: Acute sprint exercise is a time-efficient physical activity that improves cardiorespiratory fitness in younger and middle-aged adults. Growing evidence has demonstrated that acute sprint exercise provides equal to or superior health benefits compared with moderate-intensity continuous training, which will dramatically increase aerobic capacity, insulin sensitivity, and muscle capillarization. Although the beneficial effects of acute sprint exercise are well documented, the mechanisms behind how acute sprint exercise prevents disease and benefits health are less understood.

Method: We obtained differentially expressed genes in muscle (vastus lateralis) from men and women before and after an acute sprint exercise. Then, we identified hub genes from the protein–protein interaction (PPI) network of differentially expressed genes (DEGs) and key transcription factors in men and women related to acute sprint exercise. Finally, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses are performed on DEGs and sex-biased genes, respectively.

Results: First, we identified 127 sexually dimorphic genes in men (90 upregulated and 37 downregulated) and 75 genes in women (90 upregulated and 37 downregulated) in response to acute sprint exercise. Second, CEBPB, SMAD3, and CDKN1A are identified as the top three hub genes related to men-biased genes. Accordingly, the top three hub genes related to women-biased genes are JUN, ACTB, and SMAD7. In addition, CLOCK, ZNF217, and KDM2B are the top three enriched transcriptional factors in men-biased genes, while XLR, SOX2, JUND, and KLF4 are transcription factors enriched most in women-biased genes. Furthermore, based on GO and KEGG enrichment analyses, we identified potential key pathways in regulating the exercise-related response in men and women, respectively.

Conclusion: In this study, we found the difference in gene expression and enrichment pathways in muscle in men and women in response to acute sprint exercise. These results will shed new light on the mechanism underlying sex-based differences in skeletal muscle remodeling and metabolism related to acute sprint exercise, which may illustrate the mechanisms behind how acute sprint exercise prevents disease and benefits health.

Bout duration in high-intensity interval exercise modifies hematologic, metabolic and antioxidant responses

Objective

This study compared hematologic, metabolic and antioxidant responses between three high-intensity interval exercise (HIIE) trials of different bout duration and a continuous exercise trial (CON), all with equal average intensity, total work, and duration.

Methods

Eleven healthy young males performed four trials involving 20 min of cycling, either continuously (49% of power at VO₂max, PPO), or intermittently with 48 10-s bouts (HIIE10), 16 30-s bouts (HIIE30) or 8 60-s bouts (HIIE60) at 100% PPO, with a 1:1.5 work-to-recovery ratio at 15% PPO. Venous blood was obtained before, immediately after, and 1 h post-exercise to evaluate hematologic, metabolic and antioxidant responses. Blood lactate concentration was measured in capillary blood during exercise, while urine lactate was measured before and 1 h post-exercise.

Results

Post-exercise leukocyte count (mean ± SD; 9.7 ± 2.8 k μL^-1), uric acid concentration (0.35 ± 0.10 mmol L^-1), glucose concentration (6.56 ± 1.44 mmol L^-1), and plasma volume change (-13.5 ± 4.4%) were greater in HIIE60 compared to all other trials (p < 0.05). One-hour post-exercise, lymphocytes decreased below pre-exercise values in all HIIE trials, and uric acid increased in the HIIE60 trial (p < 0.05). Urine lactate concentration 1 h post-exercise increased compared to pre-exercise only in HIIE60 (19-fold, p < 0.001), and this was related with the higher blood lactate concentration during exercise in that trial.

Conclusions

These findings highlight the importance of bout duration, given that shorter bouts of HIIE (30 s or 10 s) induce lower blood cell perturbations, metabolic stress, and antioxidant responses compared to the commonly used 1-min bouts, despite equal total work, duration, and work-to-recovery ratio.

Exercise mode influences post-exercise glucose sensitivity and insulin clearance in young, healthy males and females in a sex-dependent manner: A randomized control trial

Type 2 diabetes (T2D) risk is lower in females than males. It has been reported that females have greater pancreatic 𝛽-cell function than males, which may at least in part contribute to the T2D risk in females. 𝛽-cell function is influenced by exercise training; however, previous trials comparing 𝛽-cell function between the sexes have not included participants matched for training status. Furthermore, the acute effects of different modes of exercise on 𝛽-cell function, and whether sex inherently influences these effects, are largely unexamined. Males and females (12/sex) completed a 120-min oral glucose tolerance test (OGTT) at rest (CON) and following acute bouts of high-intensity interval exercise (HIIE), moderate intensity continuous (MIC) exercise, and low-load high-repetition (LLHR) resistance exercise to assess whether sex inherently influences baseline and/or post-exercise pancreatic function in the absence of pathology. We found no sex differences in basal pancreatic 𝛽-cell function. Females had greater basal insulin clearance following MIC exercise compared to males (p = 0.01) and males tended to have a higher potentiation ratio following HIIE (p = 0.07). Females also had lower glucose sensitivity following MIC exercise compared to HIIE (p = 0.007) and LLHR (p = 0.003). Insulin clearance during the OGTT was greater following HIIE as compared with CON and MIC exercise (p = 0.02). 2-H oral glucose insulin sensitivity was greater following LLHR compared to CON (p = 0.01). Acute bouts of different modes of exercise do not differentially influence 𝛽-cell function but do influence insulin clearance and insulin sensitivity. Therefore, sex and exercise mode interact to differentially influence insulin clearance and glucose sensitivity.

Improvements in Maximal Oxygen Uptake After Sprint-Interval Training Coincide with Increases in Central Hemodynamic Factors

INTRODUCTION

Sprint-interval training has been shown to improve maximal oxygen uptake, in part through peripheral muscle adaptations that increase oxygen utilization. In contrast, the adaptations of central hemodynamic factors in this context remain unexplored.

PURPOSE

The aim of the current study was to explore the effects of sprint-interval training on maximal oxygen uptake and central hemodynamic factors.

METHODS

Healthy men and women (n = 29; mean age, 27 ± 5 yr; height, 175 ± 8 cm; body mass, 72.5 ± 12.0 kg) performed 6 wk of sprint-interval training consisting of three weekly sessions of 10-min low-intensity cycling interspersed with 3 × 30-s all-out sprints. Maximal oxygen uptake, total blood volume, and maximal cardiac output were measured before and after the intervention.

RESULTS

Maximal oxygen uptake increased by 10.3% (P < 0.001). Simultaneously, plasma volume, blood volume, total hemoglobin mass, and cardiac output increased by 8.1% (276 ± 234 mL; P < 0.001), 6.8% (382 ± 325 mL; P < 0.001), 5.7% (42 ± 41 g; P < 0.001), and 8.5% (1.0 ± 0.9 L·min-1; P < 0.001), respectively. Increased total hemoglobin mass along with measures of body surface area had a significant impact on the improvements in maximal oxygen uptake.

CONCLUSIONS

Six weeks of sprint-interval training results in significant increases in hemoglobin mass, blood volume, and cardiac output. Because these changes were associated with marked improvements in maximal oxygen uptake, we conclude that central hemodynamic adaptations contribute to the improvement in maximal oxygen uptake during sprint-interval training.

The impact of high-intensity interval training on postprandial glucose and insulin: A systematic review and meta-analysis

AIMS

We performed a systematic review and meta-analysis to investigate the effects of high-intensity interval training (HIIT) on postprandial glucose (PPG) and insulin (PPI) versus non-exercise control and moderate-intensity continuous training (MICT) in participants with both normal and impaired glucose.

METHODS

The PubMed, Scopus, and Web of Science electronic databases were searched up to October 2021 for randomized trials evaluating HIIT versus control and/or versus MICT on glucose and insulin AUC using oral glucose tolerance testing. Subgroup analyses based on intervention duration (short-duration < 8 weeks, moderate-duration ≥ 8 weeks), baseline glucose levels (normal glucose and impaired glucose) and type of HIIT (L-HIIT and SIT) were also conducted across included studies.

RESULTS

A total of 25 studies involving 870 participants were included in the current meta-analysis. HIIT effectively reduced glucose [-0.37 (95% CI -0.60 to -0.13), p = 0.002] and insulin [-0.36 (95% CI -0.68 to -0.04), p = 0.02] AUC when compared with a CON group. Reductions in glucose AUC were significant for those with impaired glucose at baseline (p = 0.03), but not for those with normal glucose levels (p = 0.11) and following moderate-duration (p = 0.01), but not short-duration interventions (p = 0.18). However, there were no differences in glucose (p = 0.76) or insulin (p = 0.43) AUC between HIIT and MICT intervention arms.

CONCLUSIONS

Our results demonstrated that both HIIT and MICT are effective for reducing postprandial glycemia and insulinemia, particularly by moderate-duration interventions, and in those with impaired glucose.

Carbohydrate-Energy Replacement Following High-Intensity Interval Exercise Blunts Next-Day Glycemic Control in Untrained Women

Background

Improved glycemic control has been reported for ∼24 h following low-volume high-intensity interval exercise (HIIE), but it is unclear if this is a direct effect of exercise or an indirect effect of the exercise-induced energy deficit. The purpose of this study was to investigate the effect of carbohydrate-energy replacement after low-volume HIIE on 24 h glycemic control in women.

Methods

Seven untrained women (age: 22 ± 2 yr; BMI: 22 ± 3 kg/m2; VO2peak: 33 ± 7 ml/kg/min) completed three 2-day trials in the mid-follicular phase of the menstrual cycle. Continuous glucose monitoring was used to measure blood glucose concentrations during, and for 24 h following three conditions: (1) HIIE followed by a high-carbohydrate energy replacement drink (EX-HC); (2) HIIE followed by a non-caloric taste-matched placebo drink (EX-NC); and (3) seated control with no drink (CTL). HIIE involved an evening session (1,700 h) of 10 × 1-min cycling efforts at ∼90% maximal heart rate with 1 min recovery. Diet was standardized and identical across all three 2-day trials, apart from the post-exercise carbohydrate drink in EX-HC, which was designed to replenish the exercise-induced energy expenditure. Postprandial glycemic responses to the following days breakfast, snack, lunch, and dinner, as well as 24 h indices of glycemic control, were analyzed.

Results

The day after HIIE, postprandial glycemia following breakfast and snack were reduced in EX-NC compared to EX-HC, as reflected by lower 3 h glucose mean (breakfast: 5.5 ± 0.5 vs. 6.7 ± 1, p = 0.01, Cohen’s d = 1.4; snack: 4.9 ± 0.3 vs. 5.7 ± 0.8 mmol/L, p = 0.02, d = 1.4) and/or area under the curve (AUC) (breakfast: 994 ± 86 vs. 1,208 ± 190 mmol/L x 3 h, p = 0.01, d = 1.5). Postprandial glycemic responses following lunch and dinner were not different across conditions (p &gt; 0.05). The 24 h glucose mean (EX-NC: 5.2 ± 0.3 vs. EX-HC: 5.7 ± 0.7 mmol/L; p = 0.02, d = 1.1) and AUC (EX-NC: 7,448 ± 425 vs. EX-HC: 8,246 ± 957 mmol/L × 24 h; p = 0.02, d = 1.1) were reduced in EX-NC compared to EX-HC.

Conclusion

Post-exercise carbohydrate-energy replacement attenuates glycemic control the day following a single session of low-volume HIIE in women.

Warm-Up With Added Respiratory Dead Space Volume Mask Improves the Performance of the Cycling Sprint Interval Exercise: Cross-Over Study

Special breathing exercises performed during warm-up lead to hypercapnia and stimulation of mechanisms leading to increased exercise performance, but the effect of a device that increases the respiratory dead space volume (ARDSv) during warm-up has not been studied. The purpose of this study was to investigate the effect of 10 min warm-up with ARDSv on performance, physiological and biochemical responses during sprint interval cycling exercise (SIE). During four laboratory visits at least 72 h apart, they completed: (1) an incremental exercise test (IET) on a cycloergometer, (2) a familiarization session, and cross-over SIE sessions conducted in random order on visits (3) and (4). During one of them, 1200 mL of ARDSv was used for breathing over a 10-min warm-up. SIE consisted of 6 × 10-s all-out bouts with 4-min active recovery. Work capacity, cardiopulmonary parameters, body temperature, respiratory muscle strength, blood acid-base balance, lactate concentration, and rating of perceived exertion (RPE) were analyzed. After warm-up with ARDSv, P ET CO2 was 45.0 ± 3.7 vs. 41.6 ± 2.5 (mm Hg) (p < 0.001). Body temperature was 0.6 (°C) higher after this form of warm-up (p < 0.05), bicarbonate concentration increased by 1.8 (mmol⋅L-1) (p < 0.01). As a result, work performed was 2.9% greater (p < 0.01) compared to the control condition. Respiratory muscle strength did not decreased. Warming up with added respiratory dead space volume mask prior to cycling SIE produces an ergogenic effect by increasing body temperature and buffering capacity.

Potential Mechanisms for How Long-Term Physical Activity May Reduce Insulin Resistance

Insulin became available for the treatment of patients with diabetes 100 years ago, and soon thereafter it became evident that the biological response to its actions differed markedly between individuals. This prompted extensive research into insulin action and resistance (IR), resulting in the universally agreed fact that IR is a core finding in patients with type 2 diabetes mellitus (T2DM). T2DM is the most prevalent form of diabetes, reaching epidemic proportions worldwide. Physical activity (PA) has the potential of improving IR and is, therefore, a cornerstone in the prevention and treatment of T2DM. Whereas most research has focused on the acute effects of PA, less is known about the effects of long-term PA on IR. Here, we describe a model of potential mechanisms behind reduced IR after long-term PA to guide further mechanistic investigations and to tailor PA interventions in the therapy of T2DM. The development of such interventions requires knowledge of normal glucose metabolism, and we briefly summarize an integrated physiological perspective on IR. We then describe the effects of long-term PA on signaling molecules involved in cellular responses to insulin, tissue-specific functions, and whole-body IR.

Affecting Effects on Affect: The Impact of Protocol Permutations on Affective Responses to Sprint Interval Exercise; A Systematic Review and Meta-Analysis of Pooled Individual Participant Data

Responses to sprint interval exercise (SIE) are hypothesized to be perceived as unpleasant, but SIE protocols are diverse, and moderating effects of various SIE protocol parameters on affective responses are unknown. We performed a systematic search to identify studies (up to 01/05/2021) measuring affective valence using the Feeling Scale during acute SIE in healthy adults. Thirteen studies involving 18 unique trials and 316 unique participant (142 women and 174 men) affective responses to SIE were eligible for inclusion. We received individual participant data for all participants from all studies. All available end-of-sprint affect scores from each trial were combined in a linear mixed model with sprint duration, mode, intensity, recovery duration, familiarization and baseline affect included as covariates. Affective valence decreased significantly and proportionally with each additional sprint repetition, but this effect was modified by sprint duration: affect decreased more during 30 s (0.84 units/sprint; 95% CI: 0.74–0.93) and 15–20 s sprints (1.02 units/sprint; 95% CI: 0.93–1.10) compared with 5–6 s sprints (0.20 units/sprint; 95% CI: 0.18–0.22) (both p < 0.0001). Although the difference between 15–20 s and 30 s sprints was also significant (p = 0.02), the effect size was trivial (d = −0.12). We observed significant but trivial effects of mode, sprint intensity and pre-trial familiarization, whilst there was no significant effect of recovery duration. We conclude that affective valence declines during SIE, but the magnitude of the decrease for an overall SIE session strongly depends on the number and duration of sprints. This information can be applied by researchers to design SIE protocols that are less likely to be perceived as unpleasant in studies of real-world effectiveness.

The Influence of Acute Sprint Interval Training on Cognitive Performance of Healthy Younger Adults

There is considerable evidence showing that an acute bout of physical exercises can improve cognitive performance, but the optimal exercise characteristics (e.g., exercise type and exercise intensity) remain elusive. In this regard, there is a gap in the literature to which extent sprint interval training (SIT) can enhance cognitive performance. Thus, this study aimed to investigate the effect of a time-efficient SIT, termed as "shortened-sprint reduced-exertion high-intensity interval training" (SSREHIT), on cognitive performance. Nineteen healthy adults aged 20-28 years were enrolled and assessed for attentional performance (via the d2 test), working memory performance (via Digit Span Forward/Backward), and peripheral blood lactate concentration immediately before and 10 min after an SSREHIT and a cognitive engagement control condition (i.e., reading). We observed that SSREHIT can enhance specific aspects of attentional performance, as it improved the percent error rate (F%) in the d-2 test (t (18) = -2.249, p = 0.037, d = -0.516), which constitutes a qualitative measure of precision and thoroughness. However, SSREHIT did not change other measures of attentional or working memory performance. In addition, we observed that the exercise-induced increase in the peripheral blood lactate levels correlated with changes in attentional performance, i.e., the total number of responses (GZ) (rm = 0.70, p < 0.001), objective measures of concentration (SKL) (rm = 0.73, p < 0.001), and F% (rm = -0.54, p = 0.015). The present study provides initial evidence that a single bout of SSREHIT can improve specific aspects of attentional performance and conforming evidence for a positive link between cognitive improvements and changes in peripheral blood lactate levels.

Acute RyR1 Ca2+ leak enhances NADH-linked mitochondrial respiratory capacity

Sustained ryanodine receptor (RyR) Ca²⁺ leak is associated with pathological conditions such as heart failure or skeletal muscle weakness. We report that a single session of sprint interval training (SIT), but not of moderate intensity continuous training (MICT), triggers RyR1 protein oxidation and nitrosylation leading to calstabin1 dissociation in healthy human muscle and in in vitro SIT models (simulated SIT or S-SIT). This is accompanied by decreased sarcoplasmic reticulum Ca²⁺ content, increased levels of mitochondrial oxidative phosphorylation proteins, supercomplex formation and enhanced NADH-linked mitochondrial respiratory capacity. Mechanistically, (S-)SIT increases mitochondrial Ca²⁺ uptake in mouse myotubes and muscle fibres, and decreases pyruvate dehydrogenase phosphorylation in human muscle and mouse myotubes. Countering Ca²⁺ leak or preventing mitochondrial Ca²⁺ uptake blunts S-SIT-induced adaptations, a result supported by proteomic analyses. Here we show that triggering acute transient Ca²⁺ leak through RyR1 in healthy muscle may contribute to the multiple health promoting benefits of exercise.