An Examination and Critique of Current Methods to Determine Exercise Intensity

Impact of continuous moderate-intensity aerobic exercise on glycemic control according to different phases of the menstrual cycle in females with type 1 diabetes

AIM

To assess the effects of continuous moderate-intensity aerobic exercise (CONT) on glycemic control in women with type 1 diabetes (T1D) across different phases of the menstrual cycle.

METHODS

Twenty-five women with T1D completed two 30-minute CONT sessions: one during the follicular phase and the other during the luteal phase. Glycemic control was assessed during exercise by plasma glucose analysis and at 24 h post-exercise by continuous glucose monitoring.

RESULTS

A decline in blood glucose levels was observed after exercise, regardless of menstrual phase, from approximately 155 mg/dL to about 110 mg/dL. In the 24 h following exercise, the incidence of hypoglycemia was low (less than 2 %); in contrast, exercise in the luteal phase tended to increase hyperglycemia compared to the previous 24 h (from 38.2 % to 44.2 %), as well as compared to the follicular phase, with higher mean blood glucose levels observed.

CONCLUSION

CONT has an immediate glucose-lowering effect regardless of menstrual cycle phase. However, while in the follicular phase TIR remains stable, in the luteal phase, it declines, with a corresponding increase in hyperglycemia, supporting the idea that exercise-induced glucose regulation varies across menstrual phases, highlighting the potential need for insulin dose adjustments depending on the cycle's phase.

Multiple Short Intervals Induce Longer Time Above 90% of Maximal Oxygen Consumption Than Long Intervals When Matched by Similar Fixed Intensity, But Not During Self-Paced Cycling Ergometry

In previous studies comparing different interval protocols for high-intensity interval training, large differences in time above 90% of maximal oxygen consumption (V˙O2max) have been observed. Differences can possibly be attributed to session design or intensity control. Twelve well-trained cyclists and triathletes (V˙O2max: 68 [6.3] mL·min-1·kg-1) performed 2 different cycling ergometry interval protocols of 3 × 13 × 30/15 seconds (short interval [SI]) and 6 × 5 minutes (long interval [LI]), each with a fixed intensity based on percentages of maximal aerobic power and self-paced approach with maximal effort. The time above 90%V˙O2max was significantly greater for SI than LI in fixed (P < .01) but not in self-paced intensity (P = .321). All physiological parameters assessed and power outputs were higher in self-paced than fixed (all P < .001; all ηp2>.795), resulting in an increased time above 90%V˙O2max for SI (1130 [204] vs 420 [259] s) and LI (1016 [312] vs 178 [159] s). When the short recovery periods are included in total interval work duration in SI, and SI and LI are matched on duration and fixed intensities (similar percentage of maximal aerobic power), SI gave greater time above 90%V˙O2max. However, when SI and LI were performed with the self-paced approach and maximal effort, the exercise intensity became higher and there were no differences in time above 90%V˙O2max.

Exercise heart rates determined by a ventilatory threshold vs. standardized equation methods in individuals with metabolic syndrome

This study aimed to compare the target heart rate (THR) for aerobic exercise based on standardized physiological maximum value percentages with the first-ventilatory-threshold heart rate (HRVT1) in individuals with metabolic syndrome. Three HRmax prediction equations were used to calculate the THR as 35%, 40% and 45% of the heart rate reserve (HRR) and 55%, 60% and 65% of the HRmax, and the results were compared with the HRVT1. The HRVT1 was measured through a CPET that complied with current guidelines and laboratory standards. In addition, the THRs calculated by combining the HRmax-measured values with standardized methods were compared with those of HRVT1 as a supplement for situations where HRmax-measured values can be evaluated but gas exchange analysis cannot be performed. According to the Fox equation, the difference between the HRVT1 and 35% HRR was not statistically significant (t = - 0.528, P = 0.600). Bland‒Altman analysis indicated that the mean difference between the two values was - 0.350, which was close to the 0th line (SD: ± 4.595; 95% CI - 1.684-0.984), with 95% limits of agreement ranging from - 9.356 to 8.656; the interclass correlation coefficient (ICC) was 0.862 (P < 0.001, 95% CI 0.766-0.920), indicating high reliability. Regarding the results, the measured values indicate that 40% HRR and 70% HRPeak showed good reliability with HRVT1 (ICC: 0.850, 95% CI 0.747-0.913; and ICC: 0.719, 95% CI 0.551-0.832, respectively). Among Chinese patients with MetS, the THR calculated by combining the standardized 35% HRR method with the Fox equation shows excellent agreement with the HRVT1 obtained from the CPET. When the HRPeak can be obtained, the THR calculated from the 40% HRR and 70% HRPeak can better estimate the HRVT1. The above results can be used to guide patients to gradually start exercise training near the VT1 in cases where CPET data cannot be obtained.

Durability of the moderate-to-heavy intensity transition can be predicted using readily available markers of physiological decoupling

PURPOSE

To assess relationships between heart rate (HR), ventilation (̇ V ˙ E), and respiratory frequency (FR) decoupling and durability of the first ventilatory threshold (VT1), and the strength of practical models to predict power output at VT1 during prolonged exercise.

METHODS

Durability of VT1 was assessed via measurements of power output at VT1 before and after ~ 2.5-h of initially moderate-intensity cycling in 51 trained cyclists, as part of four studies published elsewhere. In 12 of those participants, power output at VT1 was assessed every hour until task failure. For every assessment of power output at VT1, HR, FR, and V ˙ ̇E was measured at fixed power outputs, and thus decoupling of these variables with power output was determined. Bivariate repeated-measures correlations (rrm) between decoupling and durability of VT1 were assessed. Multivariable models were created to predict power output at VT1 during prolonged exercise using generalised estimating equations.

RESULTS

Negative correlations were observed between exercise-induced change in power output at VT1 and HR (rrm = -0.76, P < 0.001) and FR (rrm = -0.40, P = 0.013) decoupling, but not V ˙ ̇E decoupling (rrm = -0.25, P = 0.136). The final prediction model, containing baseline VT1 and peak oxygen uptake, FR decoupling, and an interaction between HR decoupling and exercise duration, effectively predicted real-time VT1 (mean absolute error, ~ 7.2 W; R2, 0.95).

CONCLUSION

HR and/or FR decoupling during controlled training sessions may be a practically useful durability assessment. Our prediction models may be an effective means of improving within-session intensity regulation and training load monitoring.

Neuromuscular fatigue in men and women during severe-intensity exercise

The aim of this study was to explore sex differences in neuromuscular fatigue during a severe-intensity cycling exercise. Twenty-four healthy participants (12 women and 12 men) cycled at 80% of the difference between gas exchange threshold and maximal power output to the limit of tolerance. Neuromuscular fatigue was assessed by the decrease in maximal voluntary contraction of the knee extensors before and after exercise, and central and peripheral fatigue was measured by the decrease in voluntary activation and quadriceps potentiated twitch force before and after exercise. Women presented shorter time to task failure (P=0.025) and lower levels of neuromuscular fatigue (P=0.006) and peripheral fatigue (P<0.001) than men. Women and men showed different patterns of muscle activation during exercise, with women presenting greater muscle activation at the beginning of exercise and sustaining this elevated muscle activation throughout exercise, while men increased muscle activation from the beginning to the end of exercise. In conclusion, women had lower levels of neuromuscular fatigue, mainly caused by lower levels of peripheral fatigue, and a different muscle activation pattern in an exhaustive severe-intensity cycling exercise.

Measurement of lactate concentration using a minimally invasive needle with non-planer optical waveguides

Traditional methods for sampling biological substance concentrations in blood are invasive and unsuitable for continuous monitoring. This paper presents a minimally invasive device equipped with optical waveguides on the surface of an acupuncture needle for measuring lactate concentration in subepidermal tissue, potentially in a continuous fashion. The device utilizes absorbance measurements, based on the correlation between absorbance and lactate concentration in tissue. The needle, with a diameter of 200 μm, exhibits good penetrability, particularly when coated with a biocompatible epoxy, which reduces insertion resistance. The experimental results demonstrate that the device can successfully measure the concentration of lactate solutions, with light intensity decreasing as the lactate concentration increases. However, challenges remain in optimizing the device to reduce optical losses and enhance measurement accuracy. Future work will focus on reducing optical loss, conducting animal experiments, and developing a miniaturized system for simultaneous measurement of multiple biological substances, aiming for practical applications in daily health monitoring.

Carbohydrate ingestion during prolonged exercise blunts the reduction in power output at the moderate-to-heavy intensity transition

PURPOSE

To determine the effect of carbohydrate ingestion during prolonged exercise on durability of the moderate-to-heavy-intensity transition and severe-intensity performance.

METHODS

Twelve trained cyclists and triathletes (10 males, 2 females;V ˙ O 2 peak, 59 ± 5 mL kg-1 min-1; training volume, 14 ± 5 h week-1) performed an incremental test and 5-min time trial (TT) without prior exercise (PRE), and after 150 min of moderate-intensity cycling, with (POSTCHO) and without (POSTCON) carbohydrate ingestion.

RESULTS

Power output at the first ventilatory threshold (VT1) was lower in POSTCHO (225 ± 36 W, ∆ -3 ± 2%, P = 0.027, n = 11) and POSTCON (216 ± 35 W, ∆ -6 ± 4%, P = 0.001, n = 12) than PRE (229 ± 37 W, n = 12), and lower in POSTCON than POSTCHO (∆ -7 ± 9 W, ∆ -3 ± 4%, P = 0.019). Mean power output in the 5-min TT was lower in POSTCHO (351 ± 53 W, ∆ -4 ± 3%, P = 0.025) and POSTCON (328 ± 63 W, ∆ -10 ± 10%, P = 0.027) than PRE (363 ± 55 W), but POSTCHO and POSTCON were not significantly different (∆ 25 ± 37 W, ∆ 9 ± 13%, P = 0.186). Blood glucose concentration was maintained in POSTCHO, and was significantly lower at the 120 and 150-min timepoint in POSTCON (P < 0.05).

CONCLUSION

These data suggest that durability of the moderate-to-heavy-intensity transition is improved with carbohydrate ingestion. This has implications for training programming and load monitoring.

The multiple linear regression model: to predict peak metabolic equivalents and peak oxygen pulse in patients with coronary artery disease after percutaneous coronary intervention

Background

The clinical indicators of patients with coronary artery disease (CAD) often affect their prognosis. Cardiopulmonary Exercise Testing (CPET) can effectively evaluate the cardiopulmonary ability of CAD patients. The objective of this research was to explore the correlation between some clinical indicators and peak metabolic equivalents (peak METs) and peak oxygen pulse (O2Ppeak) in patients with CAD. Regression equations were further constructed for indicators with significant correlations to predict peak METs and O2Ppeak.

Methods

152 CAD patients were recruited (M: F = 109:43, age = 64.47 ± 7.80 years, including 32 patients with chronic myocardial infarction, 46 with frailty, 93 with hypertension, and 48 with diabetes). All participants had blood biochemistry analysis, cardiac ultrasound, CPET and five time sit-to-stand (FTSTS) test. CPET was tested according to an incremental loading scheme of 10-15 w/min and peak METs, O2Ppeak were recorded. Stepwise multifactorial linear regression was used to determine which clinical variables should be adjusted to improve peak METs and O2Ppeak.

Results

Results of multifactorial linear regression showed 2 equations: peak METs = 6.768-0.116*BMI + 0.018*Hgb-0.026*age-0.005*Gensini score (Adjusted R2 = 0.301, F = 17.239, p < 0.001); O2Ppeak = -1.066 + 0.264*BMI + 0.049*Hgb-0.035*age (Adjusted R2 = 0.382, F = 32.106, p < 0.001).

Conclusion

BMI, Hgb, age and Gensini score can be used to predict peak METs and BMI, Hgb and age can be used to predict O2Ppeak in patients with CAD clinically. Thus, tailored exercise program should be prescribed for individual CAD patient undergoing cardiac rehabilitation and modifying clinical factors such as BMI, Hgb and Gensini score will help to improve their cardiorespiratory fitness and quality of life.

Development of the MetFlex Index™: associations between cardiometabolic risk factors and fitness using a novel approach with blood lactate

Introduction

Cardiometabolic health is declining in the U.S. and anticipated to worsen over the next 30 years. Measurements of cardiometabolic health include blood metabolite profiles. One such metabolite is blood lactate. Lactate assessment is common in critical care and performance settings but less frequently used for the general population. The delayed onset of lactate accumulation during exercise may be an indicator of cardiometabolic health. Assessing lactate during a submaximal exercise test may assist in describing cardiometabolic health status in terms of metabolic fitness and metabolic flexibility.

Objectives

To introduce the MetFlex Index™ (MFI), a novel, scalable exercise-based and marker of cardiometabolic health, and to characterize its associations with routinely assessed cardiometabolic health risk factors.

Methods

Participants completed a submaximal test on a commercial stationary cycle following assessments of body composition, anthropometrics, vital signs, and a blood draw. Lactate was collected at each stage and the 1st and 2nd lactate thresholds were described. The MFI was calculated by using the power, in Watts, attained at the 1st lactate threshold relative to the participant's Body Mass Index (BMI).

Results

Data were collected on 827 participants (43 ± 13 years, 67% male, 72% overweight or obese). MFI peaked in the 30-39 year old cohort and decreased in subsequent decades. MFI was negatively associated with most markers of anthropometry, body composition, blood pressure, and was not associated with most blood metabolites.

Discussion

The MetFlex Index™ is a novel exercise-based approach using blood lactate to characterize skeletal muscle metabolism and is associated with several cardiometabolic health indices.

Evaluating plasma lactate running speed derived parameters for predicting maximal lactate steady state in teaching horses

In humans, there is an ongoing academic discussion about measuring plasma lactate concentration ([La-]) during an incremental exercise test (IET) to establish thresholds that can predict the maximal lactate steady state (MLSS). Training studies on horses have utilized the onset of [La-] (OBLA4 mM), also known as V4, the velocity at which the [La-] of 4 mM is reached. This study assesses the effectiveness of four methods for estimating the MLSS in teaching horses. Ten teaching horses underwent a single IET to determine four exercise intensity thresholds for predicting MLSS and performed several constant intensity running bouts to obtain the MLSS. The velocity corresponding to the visual lactate threshold (VLTV) reached by the horses during IET was the intensity in the first bout. A randomized and blind trial used a visual analysis (LTV) and a bi-segmented linear regression model (LTBI). The agreement among the velocities corresponding to the V2, V4, VLTV, and VLTBI and the MLSS (VMLSS) was established using mean difference (MD), ordinary least products (OLP), and correlation coefficient (r). The average plasma [La-] at MLSS was 1.50 ± 0.37 mM, and the V4 was higher than VMLSS with an MD of 2.12 ± 0.59 m/s between them. V2 and VLTV showed the lowest mean bias when compared to the VMLSS. The V4 threshold, as determined with the IET protocol used, is unsuitable for estimating MLSS. In the exercise test protocol used in this study, predicting the VMLSS based on V2, VLTV, or VLTBI may be more accurate.

The prevalence of gas exchange data processing methods: a semi-automated scoping review

Cardiopulmonary exercise testing involves collecting variable breath-by-breath data and sometimes requiring data processing of outlier removal, interpolation, and averaging before later analysis. These data processing choices, such as averaging duration, affect calculated values such as ˙VO2max. However, assessing the implications of data processing without knowing popular methods worth comparing is difficult. In addition, such details aid study reproduction. We conducted a semi-automated scoping review of articles with exercise testing that collected data breath-by-breath from three databases. Of the 8,344 articles, 376 (mean: 4.5% and 95% confidence interval: 4.1-5.0%) and 581 (mean: 7.0% and 95% confidence interval: 6.4-7.5%) described outlier removal and interpolation, respectively. A random subset of 1,078 articles revealed (mean: 60.9% and 95% confidence interval: 57.9-63.7%) the reported averaging methods. The commonly documented outlier cutoffs were±3 or 4 SD (39.1 and 51.6%, respectively). The dominating interpolation duration and procedure were 1 s (93.9%) and linear interpolation (92.5%). Averaging methods commonly described were 30 (30.9%), 60 (12.4%), 15 (11.6%), 10 (11.0%), and 20 (8.1%) second bin averages. This shows that studies collecting breath-by-breath data often lack detailed descriptions of data processing methods, particularly for outlier removal and interpolation. While averaging methods are more commonly reported, improved documentation across all processing steps will enhance reproducibility and facilitate future research comparing data processing choices.

The Training Intensity Distribution of Marathon Runners Across Performance Levels

BACKGROUND

The training characteristics and training intensity distribution (TID) of elite athletes have been extensively studied, but a comprehensive analysis of the TID across runners from different performance levels is lacking.

METHODS

Training sessions from the 16 weeks preceding 151,813 marathons completed by 119,452 runners were analysed. The TID was quantified using a three-zone approach (Z1, Z2 and Z3), where critical speed defined the boundary between Z2 and Z3, and the transition between Z1 and Z2 was assumed to occur at 82.3% of critical speed. Training characteristics and TID were reported based on marathon finish time.

RESULTS

Training volume across all runners was 45.1 ± 26.4 km·week-1, but the fastest runners within the dataset (marathon time 120-150 min) accumulated > three times more volume than slower runners. The amount of training time completed in Z2 and Z3 running remained relatively stable across performance levels, but the proportion of Z1 was higher in progressively faster groups. The most common TID approach was pyramidal, adopted by > 80% of runners with the fastest marathon times. There were strong, negative correlations (p < 0.01, R2 ≥ 0.90) between marathon time and markers of training volume, and the proportion of training volume completed in Z1. However, the proportions of training completed in Z2 and Z3 were correlated (p < 0.01, R2 ≥ 0.85) with slower marathon times.

CONCLUSION

The fastest runners in this dataset featured large training volumes, achieved primarily by increasing training volume in Z1. Marathon runners adopted a pyramidal TID approach, and the prevalence of pyramidal TID increased in the fastest runners.

Exercise Testing for Metabolic Flexibility: Time for Protocol Standardization

Metabolic syndrome (MetS) is a combination of risk factors that contribute to the development of many of today's chronic diseases. Rates of MetS continue to increase and it is now considered a worldwide epidemic. As with many chronic diseases it may take years for symptoms and the effects of MetS to manifest into severe health problems. Therefore, early detection is paramount A recently proposed method for the early detection of MetS is the assessment of an individual's metabolic flexibility during exercise. Metabolic flexibility is defined as the ability of the body to switch between energy substrates, primarily fats and carbohydrates, to produce energy and meet metabolic demand. This provides an indication of mitochondrial health, the possible beginning point of early insulin resistance and the development of MetS.Although there is widespread use of exercise and expired gas analysis to determine metabolic flexibility, there is no consensus on the appropriate guidelines, protocol, or interpretation of the subsequent data. Studies have used a variety of different protocols involving maximal and submaximal tests with step protocols ranging from 2 to 10 min, differences in data averaging, analysis, and stoichiometric equations, as well as variations in nutritional status of participants, and mode of exercise. This has led to considerable variation in reported results. Although the use of exercise to determine metabolic flexibility and act as a possible marker of early mitochondrial dysfunction holds significant promise, more work is required to determine the optimal protocol for clinical and research purposes.

The accuracy of fixed intensity anchors to estimate lactate thresholds in recreational runners

BACKGROUND

Endurance exercise intensities can be categorized into moderate, heavy, and severe domains based on physiological responses during incremental exercise testing. Since the evaluation of metabolic thresholds is not always possible, this study assessed the accuracy of fixed intensity anchors to estimate lactate thresholds.

METHODS

165 (64 females, 101 males) recreational runners performed a maximal incremental treadmill test. The first (LT1) and second (LT2) lactate thresholds were determined as percentages of maximum heart rate (HR), oxygen consumption (VO2), and running speed, alongside the rating of perceived exertion (RPE). Sex-specific mean values were used to determine the threshold intensities and to analyze the error magnitude for each method.

RESULTS

Females had a higher relative HR, VO2, and speed at LT1 compared to males (p < 0.001). In the pooled data, the mean absolute error for estimating LT1 varied from 0.6 to 0.8 km/h for speed and 4.9-7.4 bpm for HR, while LT2 errors ranged from 0.4 to 0.8 km/h and 2.8-5.2 bpm, respectively. The speed-derived estimations yielded the smallest error magnitudes, while the RPE-derived estimations were the least accurate. Estimating the maximum speed increased the respective errors to 1.0 km/h and 8.4 bpm for LT1, and to 1.1 km/h and 6.7 bpm for LT2.

CONCLUSION

LT1 occurred at higher relative intensity in females, suggesting a need for sex-specific intensity anchors. The speed-derived estimates were the most accurate, but the estimation of maximum values impaired the prediction accuracy. Thus, the optimal method also depends on the availability of the maximum values.

Home-based exercise and PHysical activity maintenance interventiOn after livEr traNsplantation: Impact of eXercise intensity (PHOENIX-Liver)

Liver transplant recipients experience comorbidities, including impaired physical fitness, which could be managed by exercise and physical activity interventions. This study aims to evaluate the feasibility, clinical effectiveness and cost-effectiveness of a 6-month exercise intervention, followed by a 15-month tailored physical activity maintenance intervention, in de novo liver transplant recipients. This single-centre, randomised, controlled, single-blinded trial will recruit 147 adult liver transplant recipients at 3-5 months post-transplant. Participants will be randomised into (1) 6 months of enhanced usual care, not followed by a physical activity intervention (control (CON) group, n=49), (2) 6 months of moderate-intensity exercise training, followed by a physical activity intervention (moderate-intensity training (MIT) group; n=49) or (3) consecutively 3 months of moderate-intensity exercise training, 3 months of high-intensity interval training and a physical activity intervention (moderate and high-intensity training (MHIT) group; n=49). Exercise training will consist of home-based stationary bicycling and muscle-strengthening exercises, partially supervised by participants' local physiotherapists. The physical activity intervention includes an array of behaviour change techniques. Primary hypothesis: after the exercise intervention, peak oxygen uptake (V̇O2peak) will be higher in MHIT versus CON (α-level 0.05). Secondary hypotheses: after the exercise intervention, V̇O2peak will be higher in MIT versus CON and MHIT versus MIT (α-level 0.025). Secondary outcomes, assessed up to 2 years post-transplant, include physical fitness, cardiovascular and graft health, quality of life, physical activity and implementation outcomes. Trial registration number NCT06302205.

Cardiopulmonary endurance-training responsiveness of metabolic syndrome patients to individualized and standardized exercise prescriptions: a randomized controlled trial

Objective

This investigation compares the effects of two exercise prescriptions with equal energy consumption but different exercise intensity-determination methods on cardiopulmonary endurance in a population with metabolic syndrome (MetS). This investigation verified the effectiveness of individualized methods in patients with MetS undergoing moderate-intensity exercises.

Methods

The participants were randomized into a standardized group or individualized group. Exercise intensity was determined based on the heart rate reserve method in the standardized group and ventilatory threshold model in the individualized group. The two groups completed 12 weeks of an exercise prescription with equal exercise frequency and energy consumption. Using cardiopulmonary exercise testing (CPET), primary and secondary cardiovascular endurance indicators were measured. The percentage change of PeakVO2 was used to classify participants as responders and non-responders. Other markers were used in auxiliary analysis of individual training responses.

Results

A total of 40 MetS participants (75% male; mean age: 43.58 ± 11.73; body mass index: 30.39 ± 4.26) completed all exercise interventions. The PeakVO2 increased significantly (P < 0.05) in both the standardized and individualized groups. Significant improvements in peak heart rate and maximum voluntary ventilation were observed in the individualized group. Differences in training responsiveness were also observed between the standardized and individualized groups, with 70% and 90%, respectively, being classified as responders, and improvements in PeakVO2 experienced by 14.6% and 22.1%, respectively. During the training period (weeks 4-12), a significant difference in responsiveness was observed between the groups. Similar adverse changes were present in the CPET markers of adverse responders.

Conclusion

The ventilatory threshold model-based individualized method has advantages in the MetS population. However, the responsiveness to the individualized method did not reach 100% in patients with MetS.

Which Training Intensity Distribution Intervention will Produce the Greatest Improvements in Maximal Oxygen Uptake and Time-Trial Performance in Endurance Athletes? A Systematic Review and Network Meta-analysis of Individual Participant Data

BACKGROUND

Endurance athletes tend to accumulate large training volumes, the majority of which are performed at a low intensity and a smaller portion at moderate and high intensity. However, different training intensity distributions (TID) are employed to maximize physiological and performance adaptations.

OBJECTIVE

The objective of this study was to conduct a systematic review and network meta-analysis of individual participant data to compare the effect of different TID models on maximal oxygen uptake (VO2max) and time-trial (TT) performance in endurance-trained athletes.

METHODS

Studies were included if: (1) they were published in peer reviewed academic journals, (2) they were in English, (3) they were experimental or quasi-experimental studies, (4) they included trained endurance athletes, (5) they compared a polarized (POL) TID intervention to a comparator group that utilized a different TID model, (6) the duration in each intensity domain could be quantified, and (7) they reported VO2max or TT performance. Medline and SPORTDiscus were searched from inception until 11 February 2024.

RESULTS

We included 13 studies with 348 (n = 296 male, n = 52 female) recreational (n = 150) and competitive (n = 198) endurance athletes. Mean age ranged from 17.6 to 41.5 years and VO2max ranged from 46.6 to 68.3 mL·kg-1·min-1, across studies respectively. Based on the time in heart rate zone approach, there was no difference in VO2max (SMD = - 0.06, p = 0.68) or TT performance (SMD = - 0.05, p = 0.34) between POL and pyramidal (PYR) interventions. There were no statistically significant differences between POL and any of the other TID interventions. Subgroup analysis showed a statistically significant difference in the response of VO2max between recreational and competitive athletes for POL and PYR (SMD = - 0.63, p < 0.05). Competitive athletes may have greater improvements to VO2max with POL, while recreational athletes may improve more with a PYR TID.

CONCLUSIONS

Our results indicate that the adaptations to VO2max following different TID interventions are dependent on performance level. Athletes at a more competitive level may benefit from a POL TID intervention and recreational athletes from a PYR TID intervention.

How Does the Dose and Type of Exercise Impact Acute Cardiovascular Function in Healthy Individuals?

During aerobic exercise, the cardiovascular system is tasked with delivering oxygen to active skeletal muscle via muscle blood flow while regulating mean arterial blood pressure. The impact of aerobic exercise on acute cardiovascular function may be modulated by the dose and type of exercise. Acutely, dose is the product of exercise intensity and time, whereas exercise type may refer to common aerobic modalities like cycling, running, swimming, or rowing. Each modality is unique for its medium of completion as well as the implications on blood flow arising from the position of active muscle mass relative to heart level. The purpose of this review was to address how an acute exercise dose influences cardiovascular function between prominent aerobic exercise modalities in healthy individuals. Across all modalities, all doses may transiently reduce both left and right ventricular systolic and diastolic function as well as both macro- and microvascular function. However, accurately quantifying and comparing exercise dose across the literature is challenging due to methodologic differences in exercise prescription and the cardiovascular demands imposed by differing modalities of exercise. Furthermore, the potential confounding influence of cardiovascular drift alongside variations in age, the composition of cohorts with respect to biological sex, and timing of cardiovascular measures further complicates interpretation. Future work should focus on exercise intensity prescription according to modality-specific physiologic thresholds to provide comparable doses. This approach may serve to standardize the physiologic stimulus and allow for objective assessments to be compared with confidence.

High-Intensity Interval Training for Cancer Patients: A Review of Key Considerations for Exercise Prescription

BACKGROUND

High-intensity interval training (HIIT) performed before, during, and after cancer treatment can attenuate the adverse effects induced by anti-cancer drugs. A clear presentation and rationale of characteristics of HIIT variables is vital to produce the expected HIIT adaptations in cancer patients. However, there are concerns regarding the HIIT protocols used in the cancer literature.

OBJECTIVES

The aims were to (1) identify the characteristics of HIIT and the formats that have been prescribed, (2) analyze which anchors have been utilized to prescribe effort and pause intensity, (3) examine characteristics of the physical tests used for HIIT prescription, and (4) identify potential adverse events related to HIIT intervention.

METHODS

This scoping review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines, including PubMed, Scopus, and Web of Science databases.

RESULTS

A total of 51 studies were retrieved, and the following results were found: (1) Only 25 studies reported all four essential variables for HIIT prescription [effort intensity (effort duration): pause intensity (pause duration)]. Of these studies, 23 used active pause and employed the following prescription (on average): [84% (116 s): 39% (118 s)] when percentage of maximal aerobic power (MAP) [maximal/peak oxygen uptake ( V O2max/peak)/MAP] was used; [124% (161 s): 55% (142 s)] when percentage of anaerobic threshold (AT) was used; [83% (230 s): 62% (165 s)] when maximal heart rate percentage (%HRmax) was used. From these 23 studies, 12 used V O2max/peak/MAP (one of the most recommended variables for HIIT prescription). Seven studies adopted the HIIT-long format, and in the remaining five studies, the format was unclear. (2) Twenty-four studies used fractions of V O2max/peak or mechanical variables like MAP as anchors for prescribing effort intensity, two studies used AT, 20 studies used fractions of HRmax/heart rate reserve, two studies used rate of perceived exertion (RPE), while one used RPE and % V O2peak concomitantly, and two studies utilized RPE/%HRmax concomitantly. Two studies utilized passive resting, 12 studies used % V O2peak/%MAP for prescribing pause intensity, four studies used AT, seven studies used %HRmax, one study used %HRmax/% V O2peak, and two studies used absolute loads. (3) Ten studies did not report the characteristics of the physical tests employed, two studies used submaximal tests, and 39 studies utilized graded exercise tests. (4) Ten studies did not report if there were adverse events associated with the exercise program, while 34 studies did not report any adverse events.

CONCLUSIONS

Only 50% of the studies provided all the necessary variables for accurate HIIT prescription, raising concerns about the replicability, comprehension, and effective application of HIIT in cancer patients. Most of the studies that reported all variables appeared to have employed the HIIT-long format. Only a few studies used more individualized anchors (e.g., AT) to prescribe HIIT-long format for cancer patients, which is considered a very heterogeneous population.

What Is "Zone 2 Training"?: Experts' Viewpoint on Definition, Training Methods, and Expected Adaptations

BACKGROUND

The role of high-volume low-intensity training for enhancing endurance performance has gained growing interest in recent years. Specifically, so-called "zone 2 training" is currently receiving much attention, and many propose that this is the target intensity at which a large proportion of total endurance training should be performed. However, despite the popularity of this concept, there is no clear consensus among coaches, athletes, and scientists regarding the definition of zone 2 training.

PURPOSE

This commentary summarizes the perspectives, experience, and knowledge of an expert panel of 14 applied sport scientists and professional coaches with the aim of providing insight and a basis for definitional consensus on zone 2 training. Moreover, potential training strategies at this intensity are proposed, and the expected physiological adaptations when exercising at this intensity and related research gaps are also discussed.

RESULTS

Experts reached consensus that zone 2 training should preferably be performed at intensities located immediately below the first lactate or ventilatory threshold through continuous, variable, or interval-type sessions. Furthermore, experts expected a broad range of central and peripheral adaptations from zone 2 training. These expected adaptations might not be unique to zone 2 and could also be induced with sessions performed at slightly higher and lower intensities.

CONCLUSIONS

This commentary provides practical insight and unified criteria regarding the preferred intensity, duration, and session type for the optimization of zone 2 training based on the perspectives of acknowledged sport scientists and professional coaches.

Zone 2 Intensity: A Critical Comparison of Individual Variability in Different Submaximal Exercise Intensity Boundaries

Introduction: Endurance athletes often utilize low-intensity training, commonly defined as Zone 2 (Z2) within a five-zone intensity model, for its potential to enhance aerobic adaptations and metabolic efficiency. This study aimed at evaluating intra- and interindividual variability of commonly used Z2 intensity markers to assess their precision in reflecting physiological responses during training. Methods: Fifty cyclists (30 males and 20 females) performed both an incremental ramp and a step test in a laboratory setting, during which the power output, heart rate, blood lactate, ventilation, and substrate utilization were measured. Results: Analysis revealed substantial variability in Z2 markers, with the coefficients of variation (CV) ranging from 6% to 29% across different parameters. Ventilatory Threshold 1 (VT1) and maximal fat oxidation (FatMax) showed strong alignment, whereas fixed percentages of HRmax and blood lactate thresholds exhibited wide individual differences. Discussion: Standardized markers for Z2, such as fixed percentages of HRmax, offer practical simplicity but may inaccurately reflect metabolic responses, potentially affecting training outcomes. Given the considerable individual variability, particularly in markers with high CVs, personalized Z2 prescriptions based on physiological measurements such as VT1 and FatMax may provide a more accurate approach for aligning training intensities with metabolic demands. This variability highlights the need for individualized low-intensity training prescriptions to optimize endurance adaptations in cyclists, accommodating differences in physiological profiles and improving training specificity.

Cognitive and sensorimotor benefits of moderate- and high-intensity exercise are associated with specific expression of neurotrophic markers in older rats

Endurance training is strongly recommended for older adults to maintain cognitive and motor function. The respective effects of moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on improving behavioural function and cerebral plasticity remain unknown. The purpose of this study was to determine the relative effects of 4 weeks of MICT and HIIT training on endurance, sensorimotor, and cognitive performance, as well as on the expression of neurotrophic markers in the hippocampus and cerebral cortex in aged rats. Twenty-two old male Wistar rats were assigned to one of the following groups: MICT (n = 7), HIIT (n = 6), and Control (n = 9). Incremental treadmill exercise tests, the forelimb grip strength test, the adhesive removal test, and the novel object recognition test were performed. Cerebral cortex and hippocampus were then removed for ELISA and Western blot measurements. The results showed similar benefits of MICT and HIIT on sensorimotor and cognitive functions, and a greater benefit of HIIT on endurance performance. HIIT and MICT differentially promoted cortical and hippocampal neurotrophic markers, demonstrating their complementarity. However, MICT was found to be more effective in promoting a broader range of markers, suggesting its potential as an initial training strategy for older adults.

Differences in medial temporal network intrinsic connectivity after a single bout of exercise relate to fitness, memory, and affect

INTRODUCTION

Chronic exercise has been linked to structural and functional changes in the hippocampus and surrounding areas. However, less is known about how a single session of exercise can induce immediate effects that may contribute to these long-term changes.

OBJECTIVE/METHODS

Resting-state fMRI was used to investigate changes in brain networks 19 min after a 20-min bout of vigorous-intensity acute exercise. Fortyseven healthy young adults, aged 18-29, were recruited for the study.

RESULTS

Whole-brain Independent Component Analysis revealed that only the medialtemporal network-including the bilateral hippocampus, amygdala, anterior temporal lobe, and parahippocampus-exhibited a reduction in intrinsic functional connectivity. All other brain networks remained unchanged. This reduction occurred specifically during the period following exercise and became less pronounced as more time elapsed since its completion. Additionally, the significance of this change was assessed using various correlates. The reduction was less pronounced in participants with higher levels of physical fitness, better performance in post-exercise memory tests, or a more positive post-exercise affective state compared to baseline.

CONCLUSIONS

A single bout of exercise leads to specific functional changes in the medial temporal network, which may be related to individual differences in the chronic changes resulting from repeated exercise bouts over time.

What is a cycling race simulation anyway: a review on protocols to assess durability in cycling

Physiological resilience or durability is now recognised as a determinant of endurance performance such as road cycling. Reliable, ecologically valid and standardised performance tests in laboratory-based cycling protocols have to be established to investigate mechanisms underpinning, and interventions improving durability. This review aims to provide an overview of available race simulation protocols in the literature and examines its rigour around themes that influence durability including (i) exercise intensity anchoring and (ii) carbohydrate intake whilst also (iii) inspecting reliability and justification of the developed protocols. Using a systematic search approach, 48 articles were identified that met our criteria as a cycling race simulation. Most protocols presented limitations to be recommended as exercise test to investigate durability, such as not appropriately addressing the influence of exercise intensity domains by anchoring exercise intensity as % peak power or % V ˙ O2max. Ten articles provided reliability data, but only one articles under the appropriate conditions. Most studies sufficiently controlled nutrition during trials but not in the days leading to the trials or just before the trials. Thus, there is a paucity in protocols that combine justification and reliability with optimal nutritional support and mimic the true demands of a road-cycling race. This review lists an overview of protocols that researchers could use with caution to select a protocol for future experiments, but encourages further development of improved protocols, including utilisation of virtual software applications.

Validity of heart rate measurements in wrist-based monitors across skin tones during exercise

PURPOSE

To evaluate the accuracy of a wrist-based heart rate (HR) monitor at different exercise intensities across different skin tones.

METHODS

Using a cross-sectional design, we compared HR measures from the wrist-based photoplethysmography Fitbit Charge 5 to the Polar H10 chest strap at rest and during the YMCA Protocol using a recumbent cycle ergometer. Participant were grouped into three skin tone categories: light (Fitzpatrick Scale Skin Types 1+2), medium (Types 3+4), and darker skin tone (Types 5+6). HR measures using the Polar chest strap during the exercise test were categorized as <40%, 40-60%, or >60% HR reserve (HRR). Absolute error in beats per minute (bpm) between the two devices was calculated for each measure. A linear mixed effects model was used to assess interaction effects between skin tone and exercise intensity, with participants as the random effect. Bland-Altman plots were used for visual analyses.

RESULTS

Twenty-five participants [mean (SD): 25.8 (1.9) years old; 64% female] were included with 495 observations of simultaneous Fitbit and Polar HR recordings collected during exercise. During exercise, we observed a statistically significant interaction effect between skin tone and exercise intensity. Compared with light skin tone at <40% HRR, mean error was greater for medium skin tone at >60% HRR [mean error (95%CI): 11.8 (5.6-17.9) bpm, p<0.001] and darker skin tone at 40-60% HRR [7.6 (1.7-13.5) bpm, p = 0.011] and >60% HRR [11.7 (5.3-18.0) bpm, p<0.001].

CONCLUSION

HR measurement error using a wrist-based device was greater with increasing exercise intensity for people with darker skin tones.

Predicting Heart Rate Slow Component Dynamics: A Model Across Exercise Intensities, Age, and Sex

The heart rate slow component (scHR) is an intensity-dependent HR increment that emerges during constant exercises, partially dissociated from metabolism (V˙O2). The scHR has been observed during constant-workload exercise in young and older adults. Unless this scHR is accounted for, exercise prescription using HR targets lead to an undesired reduction in metabolic intensity over time.

PURPOSE

The purpose of this study is to characterize scHR across intensities, sex, and age to develop and validate a predictive equation able to maintain the desired metabolic stimulus over time in a constant aerobic exercise session.

METHODS

In our study, 66 individuals (35 females; 35 ± 13 yrs) performed the following: (i) a ramp-test for respiratory exercise threshold (GET and RCP) and maximal oxygen uptake (V˙O2max) detection, and (ii) 6 × 9-minute constant exercises at different intensities. The scHR was calculated by linear fitting from the fifth minute of exercise (bpm⋅min-1). A multiple-linear equation was developed to predict the scHR based on individual and exercise variables. The validity of the equation was tested on an independent sample by a Pearson correlation and Bland-Altman analysis between the measured and estimated HR during constant exercises.

RESULTS

The scHR increases with intensity and is larger in males (p < 0.05). A multiple-linear equation predicts the scHR based on the relative exercise intensity to RCP, age, and sex (r2 = 0.54, SEE = 0.61 bpm⋅min-1). scHR (bpm⋅min-1) = -0.0514 + (0.0240 × relative exercise intensity to RCP) - (0.0172 × age) - (0.347 × Sex (males = 0 and females score = 1)). In the independent sample, we found an excellent correlation between the measured and estimated HR (r2 = 0.98, p < 0.001) with no bias (-0.01 b·min-1, z-score= -0.04) and a fair precision (±4.09 b·min-1).

CONCLUSIONS

The dynamic of the scHR can be predicted in a heterogeneous sample accounting for the combined effects of relative intensity, sex, and age. The above equation provides the means to dynamically adapt HR targets over time, avoiding an undesired reduction in the absolute and relative training load. This strategy would allow the maintenance of the desired metabolic stimulus (V˙O2) throughout an exercise session in a heterogeneous population.

Individual variability in lactate response to cycling prescribed using physiological thresholds and peak work rate: a crossover within-participant repeated measures study

PURPOSE

(1) To determine if the blood lactate concentration ([BLa]) response is a repeatable individual trait, and (2) To examine whether threshold-based prescription (THR) reduces interindividual variability in [BLa] response compared to traditional (maximally anchored) exercise prescription (TRAD).

METHOD

A crossover within-participant repeated measures design was used to assess [BLa] during the TRAD and THR exercise in 17 participants (9 M/8F). Participants initially undertook an incremental test to exhaustion to determine peak work rate (WRpeak), a lactate threshold (LT) test and a critical power (CP) test. All baseline tests were repeated twice. Participants then completed 6 15-min bouts of continuous cycling at 65%WRpeak (TRAD; 3 bouts) and 80% of the difference (Δ80) between LT and CP (THR; 3 bouts). [BLa] response was measured at 10 and 15 min of exercise.

RESULTS

Across individuals, there was a wide range in [BLa] response, but within individual responses were repeatable. [BLa] ranges and mean individual 90% confidence interval width (CIw) were as follows: TRAD@10 min = 2.1-9.7 mmol, CIw = 0.5 mmol, THR@10 min = 3.4-9.3 mmol, CIw = 0.6 mmol, TRAD@15 min = 2.2-9.9 mmol, CIw = 0.6 mmol, THR@15 min = 3.6-12.3 mmol, CIw = 0.7 mmol. Levene's tests revealed no significant differences in the variability of [BLa] response between TRAD and THR at 10 min (F = 0.523, p = 0.475) or 15 min (F = 0.351, p = 0.558) of exercise.

CONCLUSION

Our results demonstrate that true interindividual variability in the [BLa] response to exercise exists, but failed to confirm that variability in [BLa] response is reduced with the use of THR.

Impact of High-Intensity Interval Exercise With Elastic Bands Versus Continuous Moderate-Intensity Aerobic Exercise on Glycemic Control in People With Type 1 Diabetes

BACKGROUND

Engaging in physical exercise is recommended to enhance cardiovascular health and manage blood sugar levels in people with type 1 diabetes (T1D).

HYPOTHESIS

The impact of high-intensity interval exercise with elastic bands (EB-HIIE) versus continuous moderate-intensity aerobic exercise (CONT) on glycemic control is different in men with T1D.

STUDY DESIGN

Crossover study design.

LEVEL OF EVIDENCE

Level 3.

METHODS

Participants (39 men with T1D) underwent either an EB-HIIE or a CONT session in randomized order, with a separation of ≥72 hours to avoid carry-over effects. Changes in glucose values during exercise were measured simultaneously from venous blood (YSI) and interstitial fluid (Dexcom G6 glucose sensor). Subsequent 24-hour glucose was monitored using the glucose sensor.

RESULTS

Blood glucose was lower in CONT vs EB-HIIE (P < .01). Post hoc analysis revealed clinically relevant differences during exercise (-35.1 mg/dl; P = .02), at its end (-49.5 mg/dl; P < .01), and at 10 and 20 minutes after completion (-51.2 mg/dl; P < .01 and -45.9 mg/dl; P < .01, respectively). Time-in-range 24 hours after exercise completion was significantly higher with EB-HIIE than with CONT (66.5% vs 59.3%), although both were significantly better than the previous 24 hours before exercise (50%).

CONCLUSION

Results suggest that EB-HIIE is a safe training method for male adults with diabetes, resulting in euglycemia during and immediately after exercise and improving glucose outcomes in the subsequent 24 hours.

CLINICAL RELEVANCE

This study provides new evidence and practical information on how to implement safe physical activity in daily life of patients with diabetes. EB-HIIT exhibited lower hypoglycemia risk during exercise and better glycemic control in the subsequent 24 hours. In contrast, practicing CONT exercise is associated with higher risk of hypoglycemia. Healthcare providers should take this information into account when prescribing exercise.

A case report of the female world record holder from 1,500 m to the marathon in the 75+ age category

This study assessed the cardiorespiratory fitness, running biomechanics, muscle architecture, and training characteristics of a 76-yr-old female runner who currently holds the world record 1,500 m to marathon in the women's 75-79 yr age category. Maximum oxygen uptake (V̇o2max), running economy (RE), lactate threshold (LT), lactate turnpoint (LTP), maximal heart rate (HRmax), and running biomechanics were measured during a discontinuous treadmill protocol followed by a maximal incremental test. Muscle architecture was assessed using ultrasound. The testing was done in close proximity to her world record marathon performance in 2024. V̇o2max was 47.9 mL·kg-1·min-1, and HRmax was 180 beats·min-1. At marathon speed (11.9 km·h-1) her RE was 210 mL·kg-1·km-1 and her fractional utilization was 88% of V̇o2max. Fractional utilization at LT (11.1 km·h-1) and LTP (12.5 km·h-1) were 83% and 92% of V̇o2max, respectively. Average weekly distance was 115 and 84 km·wk-1 in the 6 wk prior to the marathon world record, and 2024 World Masters Athletics Championships (where she achieved 6 gold medals out of 6 events), respectively, with on average 90%, 9%, and 1% of training time performed in the moderate, heavy, and severe intensity domain, respectively. The 76-yr-old female world-record holder 1,500 m to marathon showed the highest V̇o2max ever recorded for a female >75 yr old, a very high fractional utilization of V̇o2max at LT, LTP, and marathon pace, while RE was found to be modest compared with other world-class master and younger elite runners.NEW & NOTEWORTHY This case study investigates the physiological determinants of exceptional performance in a 76-yr-old female world-record holder across distances from 1,500 m to the marathon. It reveals the highest V̇o2max ever recorded in females aged >75 yr and exceptional fractional utilization at metabolic thresholds and marathon speed, comparable to younger world-class distance runners. The modest running economy found can be partially explained by biomechanical and training data.

Changes in Cardiorespiratory Fitness Following Exercise Training Prescribed Relative to Traditional Intensity Anchors and Physiological Thresholds: A Systematic Review with Meta-analysis of Individual Participant Data

BACKGROUND

It is unknown whether there are differences in maximal oxygen uptake ( V O2max) response when prescribing intensity relative to traditional (TRAD) anchors or to physiological thresholds (THR).

OBJECTIVES

The present meta-analysis sought to compare: (a) mean change in V O2max, (b) proportion of individuals increasing V O2max beyond a minimum important difference (MID) and (c) response variability in V O2max between TRAD and THR.

METHODS

Electronic databases were searched, yielding data for 1544 individuals from 42 studies. Two datasets were created, comprising studies with a control group ('controlled' studies), and without a control group ('non-controlled' studies). A Bayesian approach with multi-level distributional models was used to separately analyse V O2max change scores from the two datasets and inferences were made using Bayes factors (BF). The MID was predefined as one metabolic equivalent (MET; 3.5 mL kg-1 min-1).

RESULTS

In controlled studies, mean V O2max change was greater in the THR group compared with TRAD (4.1 versus 1.8 mL kg-1 min-1, BF > 100), with 64% of individuals in the THR group experiencing an increase in V O2max > MID, compared with 16% of individuals taking part in TRAD. Evidence indicated no difference in standard deviation of change between THR and TRAD (1.5 versus 1.7 mL kg-1 min-1, BF = 0.55), and greater variation in exercise groups relative to non-exercising controls (1.9 versus 1.3 mL kg-1 min-1, BF = 12.4). In non-controlled studies, mean V O2max change was greater in the THR group versus the TRAD group (4.4 versus 3.4 mL kg-1 min-1, BF = 35.1), with no difference in standard deviation of change (3.0 versus 3.2 mL kg-1 min-1, BF = 0.41).

CONCLUSION

Prescribing exercise intensity using THR approaches elicited superior mean changes in V O2max and increased the likelihood of increasing V O2max beyond the MID compared with TRAD. Researchers designing future exercise training studies should thus consider the use of THR approaches to prescribe exercise intensity where possible. Analysis comparing interventions with controls suggested the existence of intervention response heterogeneity; however, evidence was not obtained for a difference in response variability between THR and TRAD. Future primary research should be conducted with adequate power to investigate the scope of inter-individual differences in V O2max trainability, and if meaningful, the causative factors.

Setting Treadmill Intensity for Rat Aerobic Training Using Lactate and Gas Exchange Thresholds

PURPOSE

To open up new horizons of translational research, we studied the lactate threshold (LT)-dependent physiological responses and adaptations to exercise in rats, highlighting the importance of intensity-specific studies for optimizing exercise prescriptions. LT is physiologically related to the noninvasive gas exchange threshold (GET), and both thresholds are moderate-heavy-intensity boundary indices in determining an effective intensity of aerobic training in humans. Although their practical utility is presumed to extend to rats, the actual existence of GET, the thresholds' relations to maximal oxygen consumption (V̇O 2max ), and whether aerobic adaptations by training differ around the LT intensity remain uncertain.

METHODS

This study sought to identify the GET using our previously established rat LT model by combining the use of a metabolic chamber and the V-slope method, and to confirm the thresholds' relations to V̇O 2max . We investigated changes in the thresholds and V̇O 2max following 6 wk of endurance training at below or above LT intensity.

RESULTS

GET and LT were significantly correlated and agreed with high precision, although with a fixed bias. Untrained rats exhibited GET and LT at 56% and 52% of their V̇O 2max , respectively. Endurance training at supra-, but not below-, the LT intensity significantly improved V̇O 2max and both thresholds; however, their %V̇O 2max remained unaltered.

CONCLUSIONS

GET in rats is identifiable as a threshold associated with LT using the V-slope method. Furthermore, both thresholds can serve as moderate-heavy-intensity boundary indices for the aerobic training of rats. This study advances our understanding of exercise intensity regulation in rats, thereby contributing to the development of a more nuanced and effective model for exercise prescription, with implications for human health and fitness.

Using Free-Living Heart Rate Data as an Objective Method to Assess Physical Activity: A Scoping Review and Recommendations by the INTERLIVE-Network Targeting Consumer Wearables

Wearable technologies open up new avenues for the assessment of individual physical activity behaviour. Particularly, free-living heart rate (HR) data assessed by optical sensors are becoming widely available. However, while an abundancy of scientific information and guidance exists for the processing of raw acceleration data, no universal recommendations for the utilization of continuous HR recordings during free-living conditions are available. Towards Intelligent Health and Well-Being: Network of Physical Activity Assessment (INTERLIVE®) is a joint European initiative of six universities and one industrial partner. The consortium was founded in 2019 and strives towards developing best-practice recommendations in the context of consumer wearables and smartphones. The aim of this scoping review (following PRISMA-ScR procedures) and recommendations was to provide best-practice protocols for deriving individual physical activity profiles from continuous HR recordings by wearables. The recommendations were developed through an initial scoping review, grey literature searches of promotional material and user manuals of leading wearable manufacturers as well as evidence-informed discussions among the members of the INTERLIVE®-network. The scoping review was performed on the generic domains required for physical activity assessment, namely: (1) 'assessment of maximal heart rate', (2) 'determination of basal and/or resting heart rate' and (3) 'heart rate-derived intensity zones', for which we finally included a total of 72, 2 and 11 eligible papers, respectively. Gathering recent knowledge, we provide a decision tree and detailed recommendations for the analysis of free-living HR data to derive individual physical activity profiles. Moreover, we also provide examples of HR-metric calculations that help to illustrate data processing and reporting.

Detrended fluctuation analysis to determine physiologic thresholds, investigation and evidence from incremental cycling test

PURPOSE

Training zones are generally assessed by gas-exchange thresholds (GET). Several mathematical analyses of heart rate variability (HRV) are proposed for indirect GET determination. Our study aimed to investigate the accordance of the detrend fluctuation analysis (DFA α1) for determining GET with first (VT1) and second ventilatory (VT2) thresholds in well-trained subjects.

METHODS

Eighteen female and 38 male sub-elite cyclists performed a maximal incremental cycling test of 2-min stage duration with continuous gas exchange and HR measurements. Power output (PO), Oxygen uptake ( V ˙ O2) and HR at VT1 and VT2 were compared with DFA α1 0.75 (HRVT1) and 0.50 (HRVT2). Agreements between PO, V ˙ O2 and HR values were analyzed using Bland-Altman analysis.

RESULTS

Large limits of agreement between VT1 and HRVT1 were observed for measures of V ˙ O2 expressed in mL.min-1.kg-1 [- 21.3; + 14.1], HR [ 39.2; + 26.9] bpm and PO [- 118; + 83] watts. Indeed, agreements were also low between VT2 and HRVT2 for measures of V ˙ O2 [- 26.7; + 4.3] mL.min-1.kg-1, HR [- 45.5; + 10.6] bpm and PO [- 157; + 35] watts. Our results also showed a sex effect: women obtained worst predictions based on DFA α1 than men for HR (p = 0.014), PO (p = 0.044) at VT1 andV ˙ O 2 (p = 0.045), HR (p = 0.003) and PO (p = 0.004) at VT2.

CONCLUSION

There was unsatisfactory agreement between the GET and DFA α1 methods for VT1 and VT2 determination in both sex well-trained cyclists. Trial registration number 2233534 on 2024/03/05 retrospectively registered.

Physiological and perceptual response to critical power anchored HIIT: a sex comparison study

PURPOSE

The aim of this study was to test the hypothesis that using threshold-based high intensity interval training (HIITTHR) prescribed at an intensity above critical power (CP) in males and females matched for maximal oxygen uptake ( V ˙ O2max) (mL/kg lean mass/min) will yield no sex differences in time to fatigue.

METHODS

Thirteen males (mean ± SD: 22.0 ± 2.48 years, 181 ± 8.36 cm, 78.8 ± 11.4 kg) and eleven females (mean ± SD: 22.4 ± 2.69 years, 170 ± 5.73 cm, 65.2 ± 7.66 kg) initially undertook an incremental test to exhaustion to determine V ˙ O2max, and a CP test. Then, one HIIT session (4 min on, 2 min off) was performed to exhaustion at the work rate associated with 105%CP. Acute physiological and cardiovascular responses were recorded.

RESULTS

No sex differences were recorded in time to fatigue [Female vs. Male (min): 36.0 ± 18.5 vs. 39.3 ± 16.3], heart rate, rate of perceived exertion, or %oxygenated [haem]. Females displayed lower %deoxygenated [haem] at the end of interval 1, 2, 3, and 4 [Female vs. Male (%): 89.4 ± 21.2 vs. 110 ± 27.3, 92.0 ± 21.5 vs. 115 ± 27.6, 87.1 ± 23.7 vs. 112 ± 22.8, 88.9 ± 26.3 vs. 113 ± 23.5]. Large interindividual variability in performance, and physiological and perceptual response were present despite the use of threshold-based prescription.

CONCLUSION

The present study suggests that threshold-based prescription may help standardize the mean response exercise across sexes but does not eliminate physiological or perceptual variability. Furthermore, the lack of sex differences in TTF was accompanied by greater %deoxy[haem] in males, indicating tissue oxygenation is an unlikely determinant of HIIT performance. This study has been retrospectively registered at Trial Registration https://doi.org/10.17605/OSF.IO/KZVGC January 17th, 2023, following data collection but prior to data analyses.

Ventilatory thresholds in professional female soccer players

This study investigated the ventilatory thresholds (VT1 and VT2) along with the corresponding heart rates, velocities and % of V̇O2 max at which these thresholds are reached in professional female soccer players. It also examined positional differences in the aforementioned parameters. Thirty-three professional players from two teams (age range 18-31 years) were recruited. The players underwent maximal exercise testing on the treadmill for the detection of VT1 (V̇E versus V̇O2 plot) and VT2 (V̇E versus V̇CO2 plot). The test began at a speed of 6km/h and was increased by 2 km/h every 3.15 minutes, with the inclination constant at 1%. Results indicated that the players had an average V̇O2 max of 50.24 ml·kg- 1.min- 1. VT1 (% max) and VT2 (% max) were shown at 72.87% and 91.26% of V̇O2 max, respectively. The respective velocities at VT1 and VT2 were indicated at 10.85 km/h and 12.91 km/h, respectively, while the average VV̇O2 max was 14.61 km/h. The average heart rates at VT1, VT2 and V̇O2 max were 159.33, 185.15 and 192.85 beats per minute, respectively. Furthermore, analysis of variance ANOVA indicated significant differences in velocity at V̇O2max. This study provides important normative data regarding the ventilatory thresholds of female soccer players.

Blood Lactate as a Metabolic Biomarker of Anaerobic Vocal Capacity: A Pilot Study

PURPOSE

Blood lactate concentration is commonly used to assess metabolic demand and skeletal muscle training response. The objective of the pilot study was to investigate if a change in blood lactate was detectable in an anaerobically designed vocal demand task vocal capacity anaerobic task (VCAT60) and determine if the developed vocal demand task may assess the anaerobic capacity of the voice musculature, like anaerobic power tests commonly used in applied exercise science.

METHODS

A prospective repeated measures study quantified blood lactate concentration preVCAT and postVCAT60 in vocally healthy adults. The secondary outcomes included determining correlations and predictors of the change in lactate including aerodynamic, leg anaerobic capacity and anthropometric measures as well as participant reported vocal fatigue.

RESULTS

A significant positive change in lactate pre and post VCAT60 was observed (P = 0.003). Regression analyses showed that Body mass index (P = 0.003) was a predictor of the lactate concentration shift. There was no evidence of additional measured variables or their interactions being predictors of the blood lactate concentration levels detected via the vocal demand task.

CONCLUSIONS

Evidence supports the hypothesis that blood lactate may be an effective metabolic biomarker in investigating voice physiology in vivo. The VCAT60, via the shift in systemic blood lactate concentration, may provide a means from which to understand metabolic adaptations that occur in the peripheral muscles of the voice mechanism during behavioral voice intervention. Further investigations are needed to determine the clinical significance of the measured blood lactate as well as to refine the proposed anaerobic vocal demand task.

High-intensity interval aerobic exercise delays recovery from heart rate variability: a systematic review with meta-analysis

PURPOSE

The present review investigates the responses of heart rate variability indices following high-intensity interval aerobic exercise, comparing it with moderate-intensity continuous exercise in adults, with the aim of informing clinical practice.

METHODS

Searches were conducted in four databases until March 2023. Eligible studies included randomized controlled trials that assessed heart rate variability indices such as the standard deviation of normal-to-normal heartbeat intervals (SDNN), the root mean square of successive differences (RMSSD), the proportion of the number of pairs of successive normal-to-normal (NN or R-R) intervals that differ by more than 50 ms (NN50) divided by the total number of NN intervals (pNN50), power in high frequency range (HF), power in low frequency range (LF), and LF/HF before and after high-intensity interval and moderate-intensity continuous aerobic exercise. The risk of bias in included studies was evaluated using the RoB 2 tool.

RESULTS

A total of 16 studies were included in the systematic review, while 9 were included in the meta-analysis. Overall, the majority of included individuals were healthy and young. Our meta-analysis indicated that individuals who performed high-intensity interval exercise showed a slower recovery to baseline levels for HF (standardized mean difference, SMD -0.98 [95% CI -1.52 to -0.44], p < 0.001) and LF (SMD -0.42 [95% CI -0.81 to -0.02], p = 0.04) within the first 10 min of recovery, which did not occur after 1 h. Among the 16 included studies, 10 had some concerns related to bias risk, while 6 were classified as high risk.

CONCLUSIONS

High-intensity interval aerobic exercise results in delayed recovery of HF and LF indices within the first 10 min after the session. However, our review indicates that healthy individuals restore modulation of the autonomic nervous system to baseline levels after this time interval, regardless of exercise intensity.

Benefits of a group-based running session on feelings of energy and fatigue: No augmenting effect of green exercise during the defoliation season

This randomized controlled trial investigated the impact of a brief session of group-based running on feelings of energy and fatigue, comparing exercise in a local nature reserve versus an outdoor built environment, and a sedentary control condition. Sixty-six physically active university students participated, with 56 providing full data for each time point. Consistent with previous research, participants in both exercise groups reported significantly increased energy and decreased fatigue compared to those in the sedentary control group. However, the type of outdoor environment did not significantly influence the magnitude of improvements. Contrary to expectations, there was no significant difference in energy enhancement or fatigue mitigation between participants who jogged in a local nature reserve versus those who jogged on a cinder track in an urbanized area. The study discusses potential reasons for this, including seasonal variations in forest volatile organic compounds (FVOCs) concentrations, which may impact the psychological effects associated with forest environments. Further research is needed to better understand the complex relationship between exercise, environment, and feelings of energy/feelings of fatigue.

Fatigue assessment in distance runners: A scoping review of inertial sensor-based biomechanical outcomes and their relation to fatigue markers and assessment conditions

BACKGROUND

Fatigue manifests as a decline in performance during high-intensity and prolonged exercise. With technological advancements and the increasing adoption of inertial measurement units (IMUs) in sports biomechanics, there is an opportunity to enhance our understanding of running-related fatigue beyond controlled laboratory environments.

RESEARCH QUESTION

How have IMUs have been used to assess running biomechanics under fatiguing conditions?

METHODS

Following the PRISMA-ScR guidelines, our literature search covered six databases without date restrictions until September 2024. The Population, Concept, and Context criteria were used: Population (distance runners ranging from novice to competitive), Concept (fatigue induced by running a distance over 400 m), Context (assessment of fatigue using accelerometer, gyroscope, and/or magnetometer wearable devices). Biomechanical outcomes were extracted and synthesised, and interpreted in the context of three main study characteristics (cohort ability, testing environment, and the inclusion of physiological outcomes) to explore their potential role in influencing outcomes.

RESULTS

A total of 88 articles were included in the review. There was a high prevalence of treadmill-based studies (n=46, 52%), utilising only 1-2 sensors (n=69, 78%), and cohorts ranged in experience, from sedentary to elite-level runners, and were largely comprised of males (69% of all participants). The majority of biomechanical outcomes assessed showed varying responses to fatigue across studies, likely attributable to individual variability, exercise intensity, and differences in fatigue protocol settings and prescriptions. Spatiotemporal outcomes such as stride time and frequency (n=37, 42 %) and impact accelerations (n=55, 62%) were more widely assessed, with a fatigue response that appeared population and environment specific.

SIGNIFICANCE

There was notable heterogeneity in the IMU-based biomechanical outcomes and methods evaluated in this review. The review findings emphasise the need for standardisation of IMU-based outcomes and fatigue protocols to promote interpretable metrics and facilitate inter-study comparisons.

Meta-analysis of a moderate-to-vigorous physical activity intervention for academic achievement in children and adolescents

BACKGROUND

To analyze the intervention effect of moderate-to-vigorous physical activity (MVPA) on the academic performance of children and adolescents.

METHODS

Experimental studies on the effects of MVPA on the academic performance of children and adolescents were comprehensively searched in Web of Science, China Knowledge Network and other databases, and the Cochrane Risk of Bias Assessment Tool was used to assess the quality of the literature, and the Meta-analysis was performed by Review Manager 5.3.

RESULTS

1) A total of 11 high-quality literature were included, including 4552 subjects; 2) MVPA had a positive effect on the academic performance of children and adolescents (SMD=0.24; 95 %CI:0.13, 0.35, P<0.0001), with differences in the effect of different subjects, and the mathematics has the best effect (SMD=0.23; 95 %CI:0.11, 0.34, P≤0.0001), followed by reading (SMD=0.24; 95 % CI:0.02, 0.46, P<0.05), and the comprehensive achievement intervention effect was not significant (SMD=0.33; 95 % CI:-0.15, 0.80, P=0.18); 3) MVPA has the greatest impact on children aged 9-11 years (SMD=0.30; 95 %CI:0.06, 0.54, P<0.05); 4) The optimal dose of intervention for MVPA is a long cycle of 30-60 minutes per session(SMD=0.34; 95 %CI:0.12, 0.56, P<0.01), 2 times per week(SMD=0.28; 95 %CI:0.2, 0.35, P<0.001); 5) The effect of literature publication bias detection was positive.

CONCLUSION

1) MVPA has a moderate effect on promoting academic achievement in children and adolescents, with younger age groups often benefiting more than older adolescents due to age-related cognitive plasticity; 2) MVPA has limited intervention effect on the performance of other subjects, which leads to the unsatisfactory effect of the intervention on the comprehensive performance; 3) Attention should be paid to the fine control of the intensity of the physical activity to guarantee individual MVPA participation to promote the academic achievement of children and adolescents; 4) Long-term participation, 30-60 minutes per session, 2-3 times per week of MVPA has been shown to be an effective intervention dose to enhance academic performance.

Fractional utilization of the 10-minute treadmill test velocity in running performance

This study aimed to evaluate the applicability of the 10-minute submaximal treadmill test (T10 test), a self-paced test, in determining critical speed (CS) and predicting running performance. Specifically, we sought to identify the percentage of T10 velocity (vT10) that runners performed in official distance races, and to compare physiological and performance indicators between sexes. 60 recreational runners (n=34 males and n=26 females) underwent a maximum incremental test, the novel T10 test, and ran 1200-m and 2400-m on the track. Runners self-reported their best performance times. Generalized Linear Model was used to compare running performances between sexes. For both males and females, the %vT10 in 5 km, 10 km, and half-marathon races occurred at 107.5% and 106.5%, 99.9% and 100.8%, and 92.6% and 97.1%, respectively. There was no interaction effect (p=0.520) and no main effect of sex (p=0.443). There was a main effect of distance (p<0.001), indicating that %vT10 in the 5km race differed from that found in the 10 km race (p=0.012), as well as in the half-marathon (p<0.001). Our findings suggest that %vT10 values can be used to determine pace in recreational endurance runners for race distances regardless of sex.

Physiological effects of high-flow nasal cannula during sustained high-intensity exercise in healthy volunteers: a randomised crossover trial

Introduction

High-flow nasal cannula (HFNC) has increased exercise capacity in patients with chronic respiratory diseases. However, it remains unknown whether HFNC impacts respiratory physiological variables during exercise. This study aimed to evaluate the effect of HFNC on respiratory physiological variables during sustained high-intensity exercise in healthy volunteers.

Methods

We performed a single-centre, open-label, randomised crossover trial to compare HFNC (60 L·min-1) and Sham-HFNC (2 L·min-1) interventions during a constant work rate exercise (CWRET) through randomised order. The primary outcome was change in oesophageal pressure (ΔP oes), and the secondary outcomes were other variables of inspiratory effort, ventilation distribution, ventilatory variables and clinical assessment. We evaluated volunteers at seven time points (baseline=T0; CWRET=T1-T2-T3 (1, 4 and 6 min); cooldown period=T4-T5-T6 (1, 6 and 10 min)) in both interventions.

Results

14 healthy volunteers (50% women; age: 22 (21-27) years) were enrolled. Mean differences in ΔP oes decreased to favour the HFNC intervention compared to Sham-HFNC at T2 (-2.8 cmH2O; 95% CI -5.3 to -0.3), as well as the simplified oesophageal pressure-time product (sPTP) per minute at T2 (-86.1 cmH2O·s·min-1; 95% CI -146.2 to -26.1) and T3 (-79.9 cmH2O·s·min-1; 95% CI -142.3 to -17.6). The standard deviation of the Regional Ventilation Delay index was also lower with HFNC compared to Sham-HFNC (T1: -1.38; 95% CI -1.93 to -0.83; T2: -0.71; 95% CI -1.27 to -0.16). There was decreased dyspnoea to favour the HFNC, but sPTP per breath, spatial distribution ventilation indexes, ventilatory variables and clinical assessments were nonsignificant between interventions.

Conclusion

HFNC intervention reduces respiratory effort and dyspnoea and improves temporal ventilation distribution in healthy volunteers during CWRET.

Optimal intensity and type of lower limb aerobic training for patients with chronic obstructive pulmonary disease: a systematic review and network meta-analysis of RCTs

BACKGROUND

Lower limb aerobic exercise is the core component of pulmonary rehabilitation for chronic obstructive pulmonary disease (COPD) patients. The optimal intensity and type (e.g., interval or continuous) of exercise training remains to be determined.

OBJECTIVES

We aimed to evaluate the optimal intensities and types of lower limb aerobic exercise in patients with COPD.

DESIGN

Systematic review and network meta-analysis of randomized controlled trials.

DATA SOURCES AND METHODS

The PubMed, Web of Science, Embase, and the Cochrane Central Register of Controlled Trials were searched for relevant data. The interventions were classified according to their intensity and type as high-intensity interval training (HIIT), high-intensity continuous training (HICT), moderate-intensity continuous training (MICT), and low-intensity continuous training (LICT). We assessed exercise capacity using peak work rate (Wpeak) and the 6-min walking test (6-MWT). Lung function was evaluated by measuring peak minute ventilation (VE) and the percentage of predicted FEV1 (FEV1pred%). Dyspnea was assessed using the Modified Medical Research Council (mMRC) scale. Quality of life was measured with the Chronic Respiratory Questionnaire (CRQ).

RESULTS

Fifteen studies were identified (979 subjects). HIIT showed the greatest improvement in Wpeak, 6-MWT, VE, and mMRC compared to usual care (MD 18.48 (95% CI 12.35, 24.60), 67.73 (34.89, 100.57), 6.26 (2.81, 9.72), and -0.53 (-0.89, -0.17), respectively) and showed the improvement in CRQ (MD 10.80 (95% CI 1.65, 19.95)). MICT showed improvement in Wpeak and 6-MWT (MD 18.28 (95% CI 11.20, 25.22), 61.92 (28.34, 95.51)) similar to HICT (MD 16.08 (95% CI 8.19, 23.84), 64.64 (28.70, 100.57)) and showed the highest improvement in CRQ compared to usual care (MD 10.83 (95% CI 1.68, 19.98)). LICT significantly improved Wpeak compared to usual care (MD 13.47 (95% CI 4.77, 22.13)). The quality of evidence for outcomes varied from very low to moderate.

CONCLUSION

HIIT and MICT might be optimal training approaches for patients with COPD. LICT exhibited limited clinical efficacy. While HICT was as effective as MICT, it caused more dyspnea.

TRIAL REGISTRATION

This systematic review and network meta-analysis was prospectively registered with PROSPERO (No. CRD 42024520134).

Quantifying exercise intensity with fractal correlation properties of heart rate variability: a study on incremental and constant-speed running

The short-term scaling exponent of detrended fluctuation analysis (DFAα1) applied to interbeat intervals may provide a method to identify ventilatory thresholds and indicate systemic perturbation during prolonged exercise. The purposes of this study were to (i) identify the gas exchange threshold (GET) and respiratory compensation point (RCP) using DFAα1 values of 0.75 and 0.5 from incremental exercise, (ii) compare DFAα1 thresholds with DFAα1 measures during constant-speed running near the maximal lactate steady state (MLSS), and (iii) assess the repeatability of DFAα1 between MLSS trials. Twelve runners performed an incremental running test and constant-speed running 5% below, at, and 5% above the MLSS, plus a repeat trial at MLSS. During 30-min running trials near MLSS, DFAα1 responses were variable (i.e., 0.27-1.24) and affected by intensity (p = 0.031) and duration (p = 0.003). No difference in DFAα1 was detected between MLSS trials (p = 0.597). In the early phase (~ 8 min), DFAα1 measures at MLSS (0.71 [0.13]) remained higher than the DFAα1 identified at RCP from the incremental test (0.57 [0.13]; p = 0.024). In addition, following ~ 18 min of constant speed running at MLSS, DFAα1 measures (0.64 [0.14]) remained higher than 0.5 (p = 0.011)-the value thought to demarcate the boundaries between heavy and severe exercise intensities. Accordingly, using fixed DFAα1 values associated with the RCP from incremental exercise to guide constant-speed exercise training may produce a greater than expected exercise intensity, however; the dependency of DFAα1 on intensity and duration suggest its potential utility to quantify systemic perturbations imposed by continuous exercise.

Profiles of muscle-specific oxygenation responses and thresholds during graded cycling incremental test

Compared to the determination of exercise thresholds based on systemic changes in blood lactate concentrations or gas exchange data, the determination of breakpoints based on muscle oxygen saturation offers a valid alternative to provide specific information on muscle-derived thresholds. Our study explored the profiles and timing of the second muscle oxygenation threshold (MOT2) in different muscles. Twenty-six cyclists and triathletes (15 male: age = 23 ± 7 years, height = 178 ± 5 cm, body mass = 70.2 ± 5.3 kg; 11 female: age = 22 ± 4 years, height = 164 ± 4 cm, body mass = 58.3 ± 8.1 kg) performed a graded exercise test (GXT), on a cycle ergometer. Power output, blood lactate concentration, heart rate, rating of perceived exertion, skinfolds and muscle oxygen saturation were registered in five muscles (vastus lateralis, biceps femoris, gastrocnemius medialis, tibialis anterior and triceps brachii) and percentage at which MOT2 occurred for each muscle was determinated using the Exponential Dmax. The results of Statistical Parametric Mapping and ANOVA showed that, although muscle oxygenation displayed different profiles in each muscle during a GXT, MOT2 occurred at a similar percentage of the GXT in each muscle (77% biceps femoris, 75% tibalis anterior, 76% gastrocnemius medialis and 72% vastus lateralis) and it was similar that systemic threshold (73% of the GXT). In conclusion, this study showed different profiles of muscle oxygen saturation in different muscles, but without notable differences in the timing for MOT2 and concordance with systemic threshold. Finally, we suggest the analysis of the whole signal and not to simplify it to a breakpoint.

Correlation properties of heart rate variability to assess the first ventilatory threshold and fatigue in runners

PURPOSE

The short-term scaling exponent alpha1 of detrended fluctuation analysis (DFA-a1) of heart rate variability (HRV) has shown potential to delineate the first ventilatory threshold (VT1). The aims of this study were to investigate the accuracy of this method for VT1 determination in runners using a consumer grade chest belt and to explore the effects of acute fatigue.

METHODS

We compared oxygen uptake (V ˙ O2) and heart rate (HR) at gas exchange VT1 to V ˙ O2 and HR at a DFA-a1 value of 0.75. Gas exchange and HRV data were obtained from 14 individuals during a treadmill run involving two incremental ramps. Agreement was assessed using Bland-Altman analysis and linear regression.

RESULTS

Bland-Altman analysis between gas exchange and HRV V ˙ O2 and HR at VT1 during the first ramp showed a mean (95% limits of agreement) bias of -0.5 (-6.8 to 5.8) ml∙kg-1∙min-1, and -0.9 (-12.2 to 10.5) beats∙min-1, with R2 of 0.83 and 0.56, respectively. During the second ramp, the differences were -7.3 (-18.1 to 3.5) ml∙kg-1∙min-1 and -12.3 (-30.4 to 5.9) beats∙min-1, with R2 of 0.62 and 0.43, respectively.

CONCLUSION

A chest-belt derived DFA-a1 of 0.75 is closely related to gas exchange VT1, with the variability in accuracy at an individual level being similar to gas exchange methods. This suggests this to be a useful method for exercise intensity demarcation. The altered relationship during the second ramp indicates that DFA-a1 is only able to accurately demarcate exercise intensity thresholds in a non-fatigued state, but also opens opportunities for fatigue-based training prescription.

Exercise intensity matters: A review on evaluating the effects of aerobic exercise intensity on muscle-derived neuroprotective myokines

Exercise as a medical intervention is effective to help prevent and manage many chronic and complex diseases, including dementia. There is evidence to suggest that regular aerobic exercise protects against age-related brain atrophy and reduces the risk of cognitive decline. The mechanisms by which exercise infers a neuroprotective effect remain to be established but may be related to a maintenance of brain volume and neuronal survival, improved cerebrovascular density and function, and/or increased synaptic plasticity. In addition, there is growing evidence to suggest the beneficial effects of exercise on brain health and cognitive function are, at least in part, mediated by factors released by skeletal muscle during contraction. The fact that the brain responds to exercise suggests that muscle-derived peripheral factors, or "myokines," may play a key role in muscle-brain crosstalk and exercise neuroprotection. However, the most effective "dose" of aerobic exercise to promote beneficial changes in these myokine pathways is currently unknown. Specifically, most of the evidence to date is from studies that have used moderate-intensity exercise, and research investigating the merit of high-intensity exercise is scarce. Considering the well-established role of high-intensity interval training in protecting against numerous medical conditions, more research is needed to identify the most effective "dose" of exercise to improve the beneficial effects of these myokines.

Highlights

Neuroprotection through exercise: Regular aerobic exercise mitigates age-related brain atrophy and cognitive decline via multiple mechanisms, including brain volume maintenance, improved cerebrovascular function, and synaptic plasticity. Myokines as mediators: Muscle-derived factors (myokines) play a crucial role in muscle-brain crosstalk, significantly contributing to the neuroprotective effects of exercise. Intensity matters: The review underscores the necessity to define and study exercise intensity, revealing high-intensity exercise may be as effective, if not more, in promoting neuroprotective myokine levels compared to moderate-intensity exercise. Future research directions: This review emphasizes the need for well-controlled studies to explore the optimal exercise dose for enhancing myokine pathways and their implications for neurodegenerative disease prevention.

Transferability of Exercise Intensity Based on Muscle Oxygenation from Normoxia to Hypoxia in Ski-Mountaineering Athletes-Exploratory Study

Frequent changes in altitude and oxygen levels limit the practical application of traditionally derived exercise thresholds or training zones based on heart rate (HR) or blood lactate concentration (bLa). We investigated the transferability of a muscle oxygenation (SmO2)-based intensity prescription between different hypoxic conditions to assess the suitability of real-time SmO2 measurements for ski-mountaineering (SKIMO) athletes during submaximal endurance exercise. A group of 15 well-trained male SKIMO athletes performed a graded-intensity run test in normoxia (87 m ASL, FiO2 = 20.8%) to determine the anaerobic threshold (AnT) with the mod-Dmax method, and maximal lactate steady state (MLSS) assessments in acute normobaric hypoxia (3000 m ASL, FiO2 = 14.4%) with the intensity aligned to 90-105% of SmO2 at the normoxia-determined AnT. SmO2, HR, and bLa were monitored during both tests. The number of MLSS assessments without a bLa increase over 1 mmol·L-1 was reported. Paired t-tests with Cohen's d effect sizes and intraclass correlation coefficient (ICC) were computed to compare the bLa and HR at the AnT in normoxia and MLSS averages in hypoxia, as both corresponded to equivalent SmO2. Out of the 15 MLSS assessments, 11 (73.3%) were performed without a bLa increase over 1 mmol·L-1. Significant differences at equivalent SmO2 in normoxia and hypoxia were found for HR (175 ± 11.7 vs. 160 ± 14.2 bpm, p = 0.005, d = 1.02), but not for bLa (4.9 ± 1.2 vs. 5.1 ± 2.4 mmol·L-1, p = 0.845, d = -0.05). ICC(2,k) for HR and bLa were 0.56 (95% CI: -0.24, 0.85) and 0.40 (95% CI: -0.75, 0.80), respectively. The results indicate a fair transferability of a SmO2-based intensity prescription between different hypoxic conditions in well-trained SKIMO athletes during submaximal endurance exercise. The practical significance of the observations depends on the required accuracy of the exercise intensity determination.

Analysis of Physical Activity Using Wearable Health Technology in US Adults Enrolled in the All of Us Research Program: Multiyear Observational Study

BACKGROUND

To date, no studies have examined adherence to the 2018 Physical Activity Guidelines for Americans (PAGA) in real-world longitudinal settings using objectively measured activity monitoring data. This study addresses this gap by using commercial activity monitoring (Fitbit) data from the All of Us dataset.

OBJECTIVE

The primary objectives were to describe the prevalence of adherence to the 2018 PAGA and identify associated sociodemographic determinants. Additionally, we compared 3 distinct methods of processing physical activity (PA) data to estimate adherence to the 2008 PAGA.

METHODS

We used the National Institutes of Health's All of Us dataset, which contains minute-level Fitbit data for 13,947 US adults over a 7-year time span (2015-2022), to estimate adherence to PAGA. A published step-based method was used to estimate metabolic equivalents and assess adherence to the 2018 PAGA (ie, ≥150 minutes of moderate- to vigorous-intensity PA per week). We compared the step-based method, the heart rate-based method, and the proprietary Fitbit-developed algorithm to estimate adherence to the 2008 PAGA.

RESULTS

The average overall adherence to the 2018 PAGA was 21.6% (3006/13,947; SE 0.4%). Factors associated with lower adherence in multivariate logistic regression analysis included female sex (relative to male sex; adjusted odds ratio [AOR] 0.66, 95% CI 0.60-0.72; P<.001); BMI of 25.0-29.9 kg/m2 (AOR 0.53, 95% CI 0.46-0.60; P<.001), 30-34.9 kg/m2 (AOR 0.30, 95% CI 0.25-0.36; P<.001), or ≥35 kg/m2 (AOR 0.13, 95% CI 0.10-0.16; P<.001; relative to a BMI of 18.5-24.9 kg/m2); being aged 30-39 years (AOR 0.66, 95% CI 0.56-0.77; P<.001), 40-49 years (AOR 0.79, 95% CI 0.68-0.93; P=.005), or ≥70 years (AOR 0.74, 95% CI 0.62-0.87; P<.001; relative to being 18-29 years); and non-Hispanic Black race or ethnicity (AOR 0.63, 95% CI 0.50-0.79; P<.001; relative to non-Hispanic White race or ethnicity). The Fitbit algorithm estimated that a larger percentage of the sample (10,307/13,947, 73.9%; 95% CI 71.2-76.6) adhered to the 2008 PAGA compared to the heart rate method estimate (4740/13,947, 34%; 95% CI 32.8-35.2) and the step-based method (1401/13,947, 10%; 95% CI 9.4-10.6).

CONCLUSIONS

Our results show significant sociodemographic differences in PAGA adherence and notably different estimates of adherence depending on the algorithm used. These findings warrant the need to account for these disparities when implementing PA interventions and the need to establish an accurate and reliable method of using commercial accelerometers to examine PA, particularly as health care systems begin integrating wearable device data into patient health records.