Evidence-Based Effects of High-Intensity Interval Training on Exercise Capacity and Health: A Review with Historical Perspective

Oxidative Stress in Military Missions-Impact and Management Strategies: A Narrative Analysis

This narrative review comprehensively examines the impact of oxidative stress on military personnel, highlighting the crucial role of physical exercise and tailored diets, particularly the ketogenic diet, in minimizing this stress. Through a meticulous analysis of the recent literature, the study emphasizes how regular physical exercise not only enhances cardiovascular, cognitive, and musculoskeletal health but is also essential in neutralizing the effects of oxidative stress, thereby improving endurance and performance during long-term missions. Furthermore, the implementation of the ketogenic diet provides an efficient and consistent energy source through ketone bodies, tailored to the specific energy requirements of military activities, and significantly contributes to the reduction in reactive oxygen species production, thus protecting against cellular deterioration under extreme stress. The study also underlines the importance of integrating advanced technologies, such as wearable devices and smart sensors that allow for the precise and real-time monitoring of oxidative stress and physiological responses, thus facilitating the customization of training and nutritional regimes. Observations from this review emphasize significant variability among individuals in responses to oxidative stress, highlighting the need for a personalized approach in formulating intervention strategies. It is crucial to develop and implement well-monitored, personalized supplementation protocols to ensure that each member of the military personnel receives a regimen tailored to their specific needs, thereby maximizing the effectiveness of measures to combat oxidative stress. This analysis makes a valuable contribution to the specialized literature, proposing a detailed framework for addressing oxidative stress in the armed forces and opening new directions for future research with the aim of optimizing clinical practices and improving the health and performance of military personnel under stress and specific challenges of the military field.

The good, the bad and the ugly - a Swedish qualitative interview study about the landscape of meaning-imbued, exercise-related physical pain, as experienced by 'normal' gym-users

BACKGROUND

The gym is a well-known place for health promoting or rehabilitating exercise whose availability to all is regarded significant for people's personal health work and the public's health. In this context, physical pain is usually discussed as something negative that people seek to dispose of. However, certain painful experiences appear to be an appreciated part of the gym experience. To investigate this seemingly contradictory landscape of meaning-imbued physical pain, the study aims to explore the different kinds of physical pain present at the gym and their significance for exercising, as experienced by 'normal' gym-users.

METHODS

24 semi-structured in-depth interviews with active, dedicated, reasonably healthy (= normal) adult gym-users have been analyzed using qualitative content analysis from a hermeneutical stance.

RESULTS

Participants differentiate between three kinds of physical pain: the good pain of enhancement (often connected to muscle soreness and effort burn), the bad pain of impediment (primarily related to acute damage) and the composite, neutral pain of acceptance (potentially linked to all pains).

CONCLUSION

When pursuing the goal of personal health development, normal gym-users argue that exercising at the gym means to expose yourself to pain and to do so willingly, even longingly. Refusing to share this understanding may diminish people's chances to occupy the gym space and, hence, reduce their chances to promote their health.

Qualitative Description of Exercise Perceptions and Experiences Among People With Human Immunodeficiency Virus in the High-Intensity Exercise to Attenuate Limitations and Train Habits Study

BACKGROUND

The benefits of physical activity (PA), specifically exercise, among older adults in general are well known. Yet globally, there is concern regarding limited engagement in PA, increased obesity, and frailty among older people with human immunodeficiency virus related to low levels of PA.

METHODS

We conducted in-depth interviews among 30 older, sedentary people with human immunodeficiency virus participating in the ongoing High-Intensity Exercise to Attenuate Limitations and Train Habits (HEALTH study, NCT04550676) between February 2021 and August 2022. A semistructured interview guide, informed by two minds theory, which frames behavior change as an intention-behavior gap between 2 neurocognitive systems, was used to elicit data from participants. Interviews explored general exercise perceptions, self-efficacy for exercise, mobile health intervention tailoring, outcome expectations, and PA goals. Thirty interviews from 33 participants were recorded and transcribed verbatim, and deductive and inductive thematic analysis were used using Dedoose.

RESULTS

Physical activity was defined as maintaining daily living activities and addressing health goals. Previous experiences with PA varied among participants and were influenced by chronic illnesses, including human immunodeficiency virus; motivation; work commitments; interest; and social support. Reported barriers to PA included antiretroviral adverse effects, comorbidities, aging, and the COVID-19 pandemic. Changes in health status, body changes, and relationships were identified as benefits of PA. Conversations with healthcare providers supporting exercise goals were perceived to be important but rarely received by the participants.

CONCLUSION

Understanding how older people with human immunodeficiency virus perceive PA is crucial to developing tailored strategies and structuring service delivery within the healthcare setting to promote a physically active life.

Variability in exercise is linked to improved age-related dysfunctions: A potential role for the constrained-disorder principle-based second-generation artificial intelligence system

Objective: Regular physical activity (PA) promotes mental and physical health. Nevertheless, inactivity is a worldwide pandemic, and methods to augment exercise benefits are required. The constrained disorder principle (CDP) characterizes biological systems based on their inherent variability. We aimed to investigate the association between intra-individual variability in PA and disability among non-athlete adults. Methods: In this retrospective analysis of the longitudinal SHARE survey, we included non-disabled adults aged >50 with at least six visits over 14 years. Self-reported PA frequency was documented bi- to triennially. Low PA intensity was defined as vigorous PA frequency less than once a week. Stable PA was described as an unchanged PA intensity in all consecutive middle observations. The primary outcome was defined as a physical limitation in everyday activities at the end of the survey. Secondary outcomes were cognitive functions, including short-term memory, long-term memory, and verbal fluency. Results: The study included 2,049 non-disabled adults with a mean age of 53 and 49.1% women. In the initially high PA intensity group, variability in PA was associated with increased physical disability prevalence (23.3% vs. 33.2%, stable vs. unstable PA ; P<0.01; adjusted P<0.01). In the initially low PA intensity group, variability was associated with a reduced physical disability (45.6% vs. 33.3%, stable vs. unstable PA ; P=0.02; adjusted P=0.03). There were no statistically significant differences in cognitive parameters between the groups. Among individuals with the same low PA intensity at the beginning and end of follow-up, variability was associated with reduced physical disability (56.9% vs. 36.5%, stable vs. unstable PA ; P=0.02; adjusted P=0.04) and improved short-term memory (score change: -0.28 vs. +0.29, stable vs. unstable PA ; P=0.05). Conclusion: Incorporating variability into PA regimens of inactive adults may enhance their physical and cognitive benefits.

Acute Oxygen Consumption Response to Fast Start High-Intensity Intermittent Exercise

The current investigation compared the acute oxygen consumption (VO2) response of two high-intensity interval exercises (HIIE), fast start (FSHIIE), and steady power (SPHIIE), which matched w prime (W') depletion. Eight cyclists completed an incremental max test and a three-minute all-out test (3MT) to determine maximal oxygen consumption (VO2max), critical power (CP), and W'. HIIE sessions consisted of 3 X 4 min intervals interspersed by 3 min of active recovery, with W' depleted by 60% (W'target) within each working interval. SPHIIE depleted the W'target consistently throughout the 3 min intervals, while FSHIIE depleted the W'target by 50% within the first minute, with the remaining 50% depleted evenly across the remainder of the interval. The paired samples t-test revealed no differences in the percentage of training time spent above 90% of VO2max (PT ≥ 90% VO2max) between SPHIIE and FSHIIE with an average of 25.20% and 26.07%, respectively. Pairwise comparisons indicated a difference between minute 1 peak VO2, minute 2, and minute 3, while no differences were present between minutes 2 and 3. The results suggest that when HIIE formats are matched based on W' expenditure, there are no differences in PT ≥ 90% VO2max or peak VO2 during each interval.

Converging protective pathways: Exploring the linkage between physical exercise, extracellular vesicles and oxidative stress

Physical Exercise (EXR) has been shown to have numerous beneficial effects on various systems in the human body. It leads to a decrease in the risk of mortality from chronic diseases, such as cardiovascular disease, cancer, metabolic and central nervous system disorders. EXR results in improving cardiovascular fitness, cognitive function, immune activity, endocrine action, and musculoskeletal health. These positive effects make EXR a valuable intervention for promoting overall health and well-being in individuals of all ages. These beneficial effects are partially mediated by the role of the regular EXR in the adaptation to redox homeostasis counteracting the sudden increase of ROS, the hallmark of many chronic diseases. EXR can trigger the release of numerous humoral factors, e.g. protein, microRNA (miRs), and DNA, that can be shuttled as cargo of Extracellular vesicles (EVs). EVs show different cargo modification after oxidative stress stimuli as well as after EXR. In this review, we aim to highlight the main studies on the role of EVs released during EXR and oxidative stress conditions in enhancing the antioxidant enzymes pathway and in the decrease of oxidative stress environment mediated by their cargo.

β-Alanine Supplementation in Combat Sports: Evaluation of Sports Performance, Perception, and Anthropometric Parameters and Biochemical Markers-A Systematic Review of Clinical Trials

β-alanine does not have an ergogenic effect by itself, but it does as a precursor for the synthesis of carnosine in human skeletal muscle. β-alanine and carnosine together help improve the muscles' functionality, especially in high-intensity exercises such as combat sports. Therefore, β-alanine could be considered a nutritional ergogenic aid to improve sports performance in combat athletes. We aimed to critically review clinical trial evidence on the impact of β-alanine supplementation on sports performance, perception, and anthropometric parameters, as well as circulating biochemical markers in combat athletes. This systematic review was conducted following the specific methodological guidelines of the Preferred Report Items for Systematic Reviews and Meta-Analyses guidelines (PRISMA), the PICOS question model, the Critical Review Form of McMaster, and the PEDro scale. Furthermore, the Cochrane risk-of-bias assessment tool was used. The search was carried out in the SCOPUS, Web of Science (WOS), and Medline (PubMed) databases for studies published from the beginning of the database until July 31, 2023. Of the 41 registers identified, only 7 met the established criteria and were included in this systematic review. Overall, performance parameters related to strength, power, total exercise work capacity, and combat-specific parameters were significantly improved (p < 0.05). Perception parameters increased non-significantly (p > 0.05). Regarding biochemical parameters, carnosine increased significantly (p < 0.05), pH decreased non-significantly (p > 0.05), and the results for blood bicarbonate and blood lactate were heterogeneous. Finally, there was a non-significant (p > 0.05) improvement in the anthropometric parameters of lean mass and fat mass. β-alanine supplementation appears to be safe and could be a suitable nutritional ergogenic aid for combat athletes.

Effects of High-Intensity Functional Training (HIFT) on the Functional Capacity, Frailty, and Physical Condition of Older Adults with Mild Cognitive Impairment: A Blind Randomized Controlled Clinical Trial

Physical exercise has been established as an intervention in the integral approach for the physical, functional, and social health of older adults. The objective of this study was to determine the effects of a high-intensity functional training (HIFT) program on the physical condition and functional capacity of an elderly Colombian population with mild cognitive impairment. This research corresponds to a blind randomized controlled clinical trial. A total of 169 men and women aged over 65 years were evaluated and distributed in two groups: the experimental group that received a 12-week HIFT intervention (n = 82) and the control group (n = 87) that received general recommendations on the benefits of physical exercise. The outcome variables included physical condition, assessed using the Senior Fitness battery (SNB); Fried's frailty phenotype was applied, and gait and balance were assessed using the Tinetti scale. For the functional variables, activities of daily living, instrumental activities of daily living, and advanced activities of daily living were evaluated. All variables were measured pre- and post-intervention. Statistically significant improvements were observed in the IG for gait stability and balance (p < 0.001), as well as for independence in activities of daily living (p = 0.003), and instrumental and advanced activities (p < 0.001). Likewise, greater functionality was found when assessed with the SNB (p < 0.001), except for upper limb strength. The frailty classification did not show changes post-intervention (p = 0.170) nor in the group x time interaction. MANCOVA analysis showed that regardless of gender, health level, age, BMI, cognition, and health level, the HIFT intervention produced better results in functional capacity, balance, and gait (F = 0.173, p < 0.001, Wilks' λ = 88.231).

The Effect of High-Intensity Interval Training Type on Body Fat Percentage, Fat and Fat-Free Mass: A Systematic Review and Meta-Analysis of Randomized Clinical Trials

This systematic review and meta-analysis of randomized controlled trials (RCTs) compared body compositional changes, including fat mass (FM), body fat percentage (BF%), and fat-free mass (FFM), between different types of high-intensity interval training (HIIT) (cycling vs. overground running vs. treadmill running) as well as to a control (i.e., no exercise) condition. Meta-analyses were carried out using a random-effects model. The I2 index was used to assess the heterogeneity of RCTs. Thirty-six RCTs lasting between 3 to 15 weeks were included in the current systematic review and meta-analysis. RCTs that examined the effect of HIIT type on FM, BF%, and FFM were sourced from online databases including PubMed, Scopus, Web of Science, and Google Scholar up to 21 June 2022. HIIT (all modalities combined) induced a significant reduction in FM (weighted mean difference [WMD]: −1.86 kg, 95% CI: −2.55 to −1.18, p = 0.001) despite a medium between-study heterogeneity (I2 = 63.3, p = 0.001). Subgroup analyses revealed cycling and overground running reduced FM (WMD: −1.72 kg, 95% CI: −2.41 to −1.30, p = 0.001 and WMD: −4.25 kg, 95% CI: −5.90 to −2.61, p = 0.001, respectively); however, there was no change with treadmill running (WMD: −1.10 kg, 95% CI: −2.82 to 0.62, p = 0.210). There was a significant reduction in BF% with HIIT (all modalities combined) compared to control (WMD: −1.53%, 95% CI: −2.13, −0.92, p = 0.001). All forms of HIIT also decreased BF%; however, overground running induced the largest overall effect (WMD: −2.80%, 95% CI: −3.89 to −1.71, p = 0.001). All types of HIIT combined also induced an overall significant improvement in FFM (WMD: 0.51 kg, 95% CI: 0.06 to 0.95, p = 0.025); however, only cycling interventions resulted in a significant increase in FFM compared to other exercise modalities (WMD: 0.63 kg, 95% CI: 0.17 to 1.09, p = 0.007). Additional subgroup analyses suggest that training for more than 8 weeks, at least 3 sessions per week, with work intervals less than 60 s duration and separated by ≤90 s active recovery are more effective for eliciting favorable body composition changes. Results from this meta-analysis demonstrate favorable body composition outcomes following HIIT (all modalities combined) with overall reductions in BF% and FM and improved FFM observed. Overall, cycling-based HIIT may confer the greatest effects on body composition due to its ability to reduce BF% and FM while increasing FFM.

Concurrent Exercise Training: Long-Term Changes in Body Composition and Motives for Continued Participation in Women with Obesity

The purpose of this project was to examine the effect of a concurrent exercise program (sprint interval training and resistance exercise) on body composition in women with obesity and factors associated with continued exercise participation following the program. Twenty women (37.1 ± 7.4 y, height = 1.63 ± 0.09 m, weight = 98.22 ± 0.22 kg, BMI = 34.2 ± 2.50 kg/m2) participated in a 10-week exercise intervention consisting of a sprint interval treadmill protocol and resistance training three times a week totaling 30 sessions. Body composition was measured by dual-energy X-ray absorptiometry (iDXA) at pretest, 12 weeks, and six months post-intervention. Semi-structured interviews assessed participants’ perception of the program at both 12 weeks and six months. Participants significantly reduced fat mass (p < 0.001), gynoid fat mass (p < 0.010), android fat mass (p = 0.003), and visceral fat mass (p = 0.003) at 12 weeks post-test. At six months, participants maintained their reductions in fat mass (p = 0.015), visceral fat (p = 0.040) and gynoid fat mass (p = 0.032). There were no significant main time effects in lean mass (p = 0.099) or caloric intake (p = 0.053) at 12 weeks or six months. Themes that emerged from the semi-structured interviews at 12 weeks reflected enjoyment in the training, increases in competence and knowledge, as well as apprehension of continuing training on their own. At six months, themes that emerged reflected overcoming barriers, competence regarding high-intensity training, and a lack of competence to engage in resistance training. Sprint interval training coupled with resistance training is a feasible exercise protocol for women with obesity and results in reduced fat mass over six months. Improving women’s competence for training is imperative for continued participation.

Interleukin-6, undercarboxylated osteocalcin, and brain-derived neurotrophic factor responses to single and repeated sessions of high-intensity interval exercise

OBJECTIVES

The purpose of this study was to compare the effects of a single session of high-intensity interval exercise (HIIE) with 2 consecutive HIIEs, separated by 3 h of recovery, on plasma interleukin-6 (IL-6), undercarboxylated osteocalcin (ucOC), and brain-derived neurotrophic factor (BDNF) responses.

METHODS

Twenty male recreational endurance athletes completed two HIIE trials in a randomized crossover design: a single session of HIIE on the single exercise day (HIIE-S) and two sessions of HIIE 3 h apart on the double exercise day (HIIE-D). The HIIE protocol consisted of 10 × 1 min cycling at 100 % of peak oxygen uptake, with 75 s of low-intensity cycling at 60 W. Blood samples were collected to analyze IL-6, ucOC, and BDNF levels before and immediately after HIIE on the HIIE-S and before and immediately after the second HIIE on the HIIE-D.

RESULTS

Both HIIE interventions significantly increased (p &lt; 0.001) plasma IL-6 (HIIE-S 33.90 % vs HIIE-D 31.04 %; p = 0.64), ucOC (HIIE-S 37.18 % vs HIIE-D 39.54 %; p = 0.85), and BDNF levels (HIIE-S 236.01 % vs HIIE-D 216.68 %; p = 0.69), with no group effect.

CONCLUSIONS

Our results demonstrate that performing two consecutive HIIEs on the same day with a 3-h rest results in similar changes in plasma levels of IL-6, BDNF, and ucOC compared with a single session of HIIE.

Effect of Sprint Interval Training on Cardiometabolic Biomarkers and Adipokine Levels in Adolescent Boys with Obesity

This study investigated the effect of supervised sprint interval training (SIT) on different cardiometabolic risk factors and adipokines in adolescent boys with obesity. Thirty-seven boys were allocated to either a SIT group (13.1 ± 0.3 years; body mass index [BMI]: 30.3 ± 0.9 kg·m^-2) or a control group (CONT) (13.7 ± 0.4 years; BMI: 32.6 ± 1.6 kg·m^-2). The SIT group performed 4-6 × 30 s all-out cycling sprints, interspersed with 4 min rest, for 3 sessions/week, during a 12-week period, while the non-exercising CONT group maintained a habitual lifestyle. Anthropometric measurements, triglycerides, fasting insulin and glucose, total cholesterol (TC), high- (HDLc) and low-density (LDLc) cholesterol, leptin and adiponectin in blood, cardiorespiratory fitness (CRF), and a metabolic syndrome severity risk score (MSSS) were calculated before and after the 12-week period. Compared to baseline values, a significant reduction in MSSS was seen in the SIT group after intervention. LDLc showed favorable changes in SIT compared to CONT (-0.06 ± 0.1 vs. 0.19 ± 0.01 mmol·L^-1; p = 0.025). Additionally, CRF increased in the SIT group compared to the CONT group (5.2 ± 1.1 vs. -2.1 ± 1.1 mL·min^-1·kg^-1, p < 0.001). Moreover, a 12-week all-out SIT training effectively improves cardiometabolic health in adolescent boys with obesity.

Very Low-Volume, High-Intensity Interval Training Mitigates Negative Health Impacts of COVID-19 Pandemic-Induced Physical Inactivity

Initially, we aimed to investigate the impact of a one-year worksite low-volume, high-intensity interval training (LOW-HIIT) on cardiometabolic health in 114 sedentary office workers. Due to the COVID-19 pandemic outbreak, LOW-HIIT was discontinued after 6 months and participants were followed up for 6 months to analyze physical activity/exercise behavior and outcome changes during lockdown. Health examinations, including cardiopulmonary exercise testing and the assessment of cardiometabolic markers were performed baseline (T-1), after 6 months (T-2, termination of worksite LOW-HIIT) and 12 months (T-3, follow-up). Cycle ergometer LOW-HIIT (5 × 1 min at 85-95% HR_max) was performed 2×/week. For follow-up analyses, participants were classified into three groups: HIIT-group (continued home-based LOW-HIIT), EX-group (continued other home-based exercises), and NO-EX-group (discontinued LOW-HIIT/exercise). At T-2, VO_2max (+1.5 mL/kg/min, p = 0.002), mean arterial blood pressure (MAB, -4 mmHg, p < 0.001), HbA_1c (-0.2%, p = 0.005) and self-reported quality of life (QoL, +5 points, p < 0.001) were improved. At T-3, HIIT-group maintained VO_2max and QoL and further improved MAB. EX-group maintained MAB and QoL but experienced a VO_2max decrease. In NON-EX, VO_2max, MAB and QoL deteriorated. We conclude that LOW-HIIT can be considered a promising option to improve cardiometabolic health in real-life conditions and to mitigate physical inactivity-related negative health impacts during lockdowns.

Effects of high-intensity interval training (HIIT) and sprint interval training (SIT) on fat oxidation during exercise: a systematic review and meta-analysis

OBJECTIVE

To investigate the effects of high-intensity interval training (HIIT) and sprint interval training (SIT) on fat oxidation during exercise (FatOx) and how they compare with the effects of moderate-intensity continuous training (MICT).

DESIGN

Systematic review and meta-analysis.

DATA SOURCES

Academic Search Ultimate, CINAHL, Networked Digital Library of Theses and Dissertations, Open Access Theses and Dissertations, OpenDissertations, PubMed/MEDLINE, Scopus, SPORTDiscus and Web of Science.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies using a between-group design, involving adult participants who were not trained athletes, and evaluating effects of HIIT or SIT on FatOx (vs no exercise or MICT) were included.

RESULTS

Eighteen studies of fair-to-good quality were included; nine comparing HIIT or SIT with no exercise and eleven comparing HIIT or SIT with MICT. A significant pooled effect of these types of interval training on FatOx was found (mean difference in g/min (MD)=0.08; 95% confidence interval (CI) 0.04 to 0.12; p<0.001). Significant effects were found for exercise regimens lasting ≥4 weeks, and they increased with every additional week of training (β=0.01; 95% CI 0.00 to 0.02; p=0.003). HIIT and/or SIT were slightly more effective than MICT (MD=0.03; 95% CI 0.01 to 0.05; p=0.005). The effects on FatOx were larger among individuals with overweight/obesity.

CONCLUSION

Engaging in HIIT or SIT can improve FatOx, with larger effects expected for longer training regimens and individuals with overweight/obesity. While some effects seem small, they may be important in holistic approaches to enhance metabolic health and manage obesity.

Six sessions of low-volume high-intensity interval exercise improves resting fat oxidation

It remains unclear whether a practical model of low-volume high-intensity interval exercise improves resting fat oxidation (FatOx) which is associated with metabolic health. We aimed to determine the effects of a short-term practical model of high-intensity interval training (HIIT) on resting FatOx in young, healthy males. Thirty healthy males were randomly assigned to either single (HIITsingle; n=13) or double HIIT (HIITdouble; n=17) group. The HIITsingle group trained once a day, 3 days/week for 2 weeks, whilst the HIITdouble group performed 6 sessions of high-intensity exercise over 5 days by exercising twice a day every second day. Both groups completed 6 high-intensity exercise sessions consisting of 10×60 s of cycling at peak power output, interspersed by 75 s cycling at 60 W. With 1% false discovery rate (FDR) significance threshold, resting respiratory exchange ratio similarly decreased in HIITsingle (pre=0.83±0.03 vs post=0.80±0.03) and HIITdouble group (pre=0.82±0.04 vs post=0.80±0.02) [(p=0.001; partial eta squared () =0.310, FDR-adjusted p value=0.005)]. Resting FatOx increased similarly in HIITsingle (pre=1.07±0.39 mg·kg-1 fat free mass (FFM)·min-1 vs post=1.44±0.36 mg·kg-1 FFM·min-1) and HIITdouble group (pre=1.35±0.45 mg·kg-1 FFM·min-1 vs post=1.52±0.29 mg·kg-1 FFM·min-1) [(p<0.001; =0.411, FDR-adjusted p value=0.005)]. Our results demonstrate that only six sessions of a practical model of low-volume high-intensity exercise improves resting FatOx in young, healthy males.

Exercise Dose Equalization in High-Intensity Interval Training: A Scoping Review

Based on comparisons to moderate continuous exercise (MICT), high-intensity interval training (HIIT) is becoming a worldwide trend in physical exercise. This raises methodological questions related to equalization of exercise dose when comparing protocols. The present scoping review aims to identify in the literature the evidence for protocol equalization and the soundness of methods used for it. PubMed and Scopus databases were searched for original investigations comparing the effects of HIIT to MICT. A total of 2041 articles were identified, and 169 were included. Of these, 98 articles equalized protocols by utilizing energy-based methods or exercise volume (58 and 31 articles, respectively). No clear consensus for protocol equalization appears to have evolved over recent years. Prominent equalization methods consider the exercise dose (i.e., energy expenditure/production or total volume) in absolute values without considering the nonlinear nature of its relationship with duration. Exercises resulting from these methods induced maximal exertion in HIIT but low exertion in MICT. A key question is, therefore, whether exercise doses are best considered in absolute terms or relative to individual exercise maximums. If protocol equalization is accepted as an essential methodological prerequisite, it is hypothesized that comparison of program effects would be more accurate if exercise was quantified relative to intensity-related maximums.

Methods to match high-intensity interval exercise intensity in hypoxia and normoxia - A pilot study

The aim of this study was to compare high-intensity interval exercise (HIIE) sessions prescribed on the basis of a maximal value (peak power output, PPO) and a submaximal value (lactate threshold, LT) derived from graded exercise tests (GXTs) in normoxia and hypoxia. Methods: A total of ten males (aged 18–37) volunteered to participate in this study. The experimental protocol consisted of a familiarization procedure, two GXTs under normoxia (FiO₂ = 0.209) and two GXTs under normobaric hypoxia (FiO2 = 0.140), and three HIIE sessions performed in a random order. The HIIE sessions included one at hypoxia (HY) and two at normoxia (one matched for the absolute intensity in hypoxia, designated as NA, and one matched for the relative intensity in hypoxia, designated as NR). Results: The data demonstrated that there was significant lower peak oxygen uptake (V̇O_2peak), peak heart rate (HR_peak), PPO, and LT derived from GXTs in hypoxia, with higher respiratory exchange ratio (RER), when compared to those from GXTs performed in normoxia (p < 0.001). Among the three HIIE sessions, the NA session resulted in lower percentage of HR_peak (85.0 ± 7.5% vs 94.4 ± 5.0%; p = 0.002) and V̇O_2peak (74.1 ± 9.1% vs 88.7 ± 7.7%; p = 0.005), when compared to the NR session. HIIE sessions in HY and NR resulted in similar percentage of HR_peak and V̇O_2peak, as well as similar rating of perceived exertion and RER. The blood lactate level increased immediately after all the three HIIE sessions (p < 0.001), while higher blood lactate concentrations were observed immediately after the HY (p = 0.0003) and NR (p = 0.014) sessions when compared with NA. Conclusion: Combining of PPO and LT derived from GXTs can be used to prescribe exercise intensity of HIIE in hypoxia.

Physiological Responses to Low-Volume Interval Training in Women

Interval training is a form of exercise that involves intermittent bouts of relatively intense effort interspersed with periods of rest or lower-intensity exercise for recovery. Low-volume high-intensity interval training (HIIT) and sprint interval training (SIT) induce physiological and health-related adaptations comparable to traditional moderate-intensity continuous training (MICT) in healthy adults and those with chronic disease despite a lower time commitment. However, most studies within the field have been conducted in men, with a relatively limited number of studies conducted in women cohorts across the lifespan. This review summarizes our understanding of physiological responses to low-volume interval training in women, including those with overweight/obesity or type 2 diabetes, with a focus on cardiorespiratory fitness, glycemic control, and skeletal muscle mitochondrial content. We also describe emerging evidence demonstrating similarities and differences in the adaptive response between women and men. Collectively, HIIT and SIT have consistently been demonstrated to improve cardiorespiratory fitness in women, and most sex-based comparisons demonstrate similar improvements in men and women. However, research examining insulin sensitivity and skeletal muscle mitochondrial responses to HIIT and SIT in women is limited and conflicting, with some evidence of blunted improvements in women relative to men. There is a need for additional research that examines physiological adaptations to low-volume interval training in women across the lifespan, including studies that directly compare responses to MICT, evaluate potential mechanisms, and/or assess the influence of sex on the adaptive response. Future work in this area will strengthen the evidence-base for physical activity recommendations in women.