Reducing the intensity and volume of interval training diminishes cardiovascular adaptation but not mitochondrial biogenesis in overweight/obese men

NAD+ homeostasis and its role in exercise adaptation: A comprehensive review

Nicotinamide adenine dinucleotide (NAD+) is a crucial coenzyme involved in catalyzing cellular redox reactions and serving as a substrate for NAD+-dependent enzymes. It plays a vital role in maintaining tissue homeostasis and promoting healthy aging. Exercise, a well-established and cost-effective method for enhancing health, can influence various pathways related to NAD+ metabolism. Strategies such as supplementing NAD+ precursors, modulating NAD+ synthesis enzymes, or inhibiting enzymes that consume NAD+ can help restore NAD+ balance and improve exercise performance. Various overlapping signaling pathways are known to play a crucial role in the beneficial effects of both NAD+ and exercise on enhancing health and slowing aging process. Studies indicate that a combined strategy of exercise and NAD+ supplementation could synergistically enhance athletic capacity. This review provides an overview of current research on the interactions between exercise and the NAD+ network, underscoring the significance of NAD+ homeostasis in exercise performance. It also offers insights into enhancing exercise capacity and improving aging-related diseases through the optimal use of exercise interventions and NAD+ supplementation methods.

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.

Exercise training and changes in skeletal muscle mitochondrial proteins: from blots to "omics"

Mitochondria are essential, membrane-enclosed organelles that consist of ∼1100 different proteins, which allow for many diverse functions critical to maintaining metabolism. Highly metabolic tissues, such as skeletal muscle, have a high mitochondrial content that increases with exercise training. The classic western blot technique has revealed training-induced increases in the relatively small number of individual mitochondrial proteins studied (∼5% of the >1100 proteins in MitoCarta), with some of these changes dependent on the training stimulus. Proteomic approaches have identified hundreds of additional mitochondrial proteins that respond to exercise training. There is, however, surprisingly little crossover in the mitochondrial proteins identified in the published human training studies. This suggests that to better understand the link between training-induced changes in mitochondrial proteins and metabolism, future studies need to move beyond maximizing protein detection to adopting methods that will increase the reliability of the changes in protein abundance observed.

Enhancing cardiometabolic health: unveiling the synergistic effects of high-intensity interval training with spirulina supplementation on selected adipokines, insulin resistance, and anthropometric indices in obese males

This study investigated the combined effects of 12 weeks of high-intensity interval training (HIIT) and spirulina supplementation on adipokine levels, insulin resistance, anthropometric indices, and cardiorespiratory fitness in 44 obese males (aged 25-40 years). The participants were randomly assigned to one of four groups: control (CG), supplement (SG), training (TG), or training plus supplement (TSG). The intervention involved daily administration of either spirulina or a placebo and HIIT three times a week for the training groups. Anthropometric indices, HOMA-IR, VO2peak, and circulating adipokines (asprosin and lipocalin2, omentin-1, irisin, and spexin) were measured before and after the 12-week intervention. Post-intervention analysis indicated differences between the CG and the three interventional groups for body weight, fat-free mass (FFM), percent body fat (%BF), HOMA-IR, and adipokine levels (p < 0.05). TG and SG participants had increased VO2peak (p < 0.05). Spirulina supplementation with HIIT increased VO2peak, omentin-1, irisin, and spexin, while causing decreases in lipocalin-2 and asprosin levels and improvements in body composition (weight, %fat), BMI, and HOMA-IR. Notably, the combination of spirulina and HIIT produced more significant changes in circulating adipokines and cardiometabolic health in obese males compared to either supplementation or HIIT alone (p < 0.05). These findings highlight the synergistic benefits of combining spirulina supplementation with HIIT, showcasing their potential in improving various health parameters and addressing obesity-related concerns in a comprehensive manner.

Shorter Versus Longer Durations of Rowing-Based Interval Exercise Attenuate the Physiological and Perceptual Response

Purpose: This study compared physiological and perceptual variables between short and long durations of rowing-based high intensity interval exercise (HIIE). Methods: Fourteen active adults (age = 26.4 ± 7.2 yr) performed incremental rowing exercise to fatigue to measure maximal oxygen uptake (VO2max) and peak power output (PPO). The subsequent 20 min sessions required HIIE (eight 60 s efforts at 85%PPO with 90 s of active recovery at 20%PPO or 24 20 s efforts at 85%PPO with 30 s of active recovery at 20%PPO) or moderate intensity continuous exercise (MICE) at 40%PPO. During exercise, VO2, heart rate (HR), blood lactate concentration (BLa), rating of perceived exertion (RPE), and affective valence were measured. Results: Data show significantly (p < 0.001) higher peak VO2 (84 ± 7 vs. 76 ± 5%VO2peak, d = 0.99), peak HR (94 ± 4%HRpeak vs. 90 ± 4%HRpeak, d = 1.12), BLa (7.0 ± 2.5 mM vs. 4.1 ± 1.0 mM, d = 1.22), end-exercise RPE (12.8 ± 2.0 vs. 11.0 ± 1.7, d = 1.29), and lower affective valence (2.1 ± 1.6 vs. 2.9 ± 1.2, d = 0.61) with long versus short HIIE. Time spent above 85%HRpeak was significantly higher (p < 0.001) in short versus long HIIE (606 ± 259 vs. 448 ± 26 s, d = 0.91). Conclusion: Longer rowing-based intervals elicit greater cardiometabolic and perceptual strain versus shorter efforts, making the latter preferable to optimize perceptual responses to HIIE.

A systematic review and meta-analysis of the SIRT1 response to exercise

Sirtuin 1 (SIRT1) is a key physiological regulator of metabolism and a target of therapeutic interventions for cardiometabolic and ageing-related disorders. Determining the factors and possible mechanisms of acute and adaptive SIRT1 response to exercise is essential for optimising exercise interventions aligned to the prevention and onset of disease. Exercise-induced SIRT1 upregulation has been reported in animals, but, to date, data in humans have been inconsistent. This exploratory systematic review and meta-analysis aims to assess various exercise interventions measuring SIRT1 in healthy participants. A total of 34 studies were included in the meta-analysis (13 single bout exercise, 21 training interventions). Studies were grouped according to tissue sample type (blood, muscle), biomarkers (gene expression, protein content, enzyme level, enzyme activity), and exercise protocols. A single bout of high-intensity or fasted exercise per se increases skeletal muscle SIRT1 gene expression as measured by qPCR or RT-PCR, while repeated resistance training alone increases blood SIRT1 levels measured by ELISA. A limited number of studies also show a propensity for an increase in muscle SIRT1 activity as measured by fluorometric or sirtuin activity assay. In conclusion, exercise acutely upregulates muscle SIRT1 gene expression and chronically increases SIRT1 blood enzyme levels.

Comparison of the acute physiological and perceptual responses between resistance-type and cycling high-intensity interval training

Purpose: The purpose of the present study was to compare the acute physiological and perceptual responses between resistance-type high-intensity interval training (R-HIIT)and cycling high-intensity interval training (C-HIIT).

Methods: Twelve healthy and active men randomly performed C-HIIT and R-HIIT. The C-HIIT protocol was performed on a cycle ergometer and consisted of ten 60 s working intervals at 90% PPO separated by a 60 s active recovery at 25% PPO. The R-HIIT protocol consisted of ten 60 s working intervals (barbell back squat with a load of 20% bodyweight, maximum 30 reps) separated by 60 s passive recovery period in an unloaded standing position. Oxygen consumption (V˙O₂), heart rate (HR), energy expenditure (EE) and rating of perceived exertion (RPE) were measured during exercise. Blood lactate concentration (Blac), serum testosterone and cortisol, and heart rate variability (HRV) were measured before and after exercise.

Results: Peak (p < 0.05) and average V˙O₂ (p < 0.001), aerobic (p < 0.001) and total EE (p < 0.05) were higher during C-HIIT compared to R-HIIT. Blac after exercise (p < 0.05) and anaerobic glycolytic EE (p < 0.05) during exercise were higher in R-HIIT compared to C-HIIT. No differences (p > 0.05) in peak and average HR, serum testosterone and cortisol, HRV, and RPE responses were observed between C-HIIT and R-HIIT.

Conclusion: The R-HIIT protocol can elicit similar cardiovascular, hormones, and perceptual responses as C-HIIT but with a higher contribution to the anaerobic glycolysis energy system. In contrast, C-HIIT is superior to R-HIIT for increasing oxygen consumption during exercise. Therefore, the two types of HIIT may lead to different metabolic and neuromuscular adaptations.

Risk of bias and reporting practices in studies comparing VO2max responses to sprint interval vs. continuous training: A systematic review and meta-analysis

BACKGROUND

It remains unclear whether studies comparing maximal oxygen uptake (VO2max) response to sprint interval training (SIT) vs. moderate-intensity continuous training (MICT) are associated with a high risk of bias and poor reporting quality. The purpose of this study was to evaluate the risk of bias and quality of reporting in studies comparing changes in VO2max between SIT and MICT.

METHODS

We conducted a comprehensive literature search of 4 major databases: AMED, CINAHL, EMBASE, and MEDLINE. Studies were excluded if participants were not healthy adult humans or if training protocols were unsupervised, lasted less than 2 weeks, or utilized mixed exercise modalities. We used the Cochrane Collaboration tool and the CONSORT checklist for non-pharmacological trials to evaluate the risk of bias and reporting quality, respectively.

RESULTS

Twenty-eight studies with 30 comparisons (3 studies included 2 SIT groups) were included in our meta-analysis (n = 360 SIT participants: body mass index (BMI) = 25.9 ± 3.7 kg/m2, baseline VO2max = 37.9 ± 8.0 mL/kg/min; n = 359 MICT participants: BMI = 25.5 ± 3.8 kg/m2, baseline VO2max = 38.3 ± 8.0 mL/kg/min; all mean ± SD). All studies had an unclear risk of bias and poor reporting quality.

CONCLUSION

Although we observed a lack of superiority between SIT and MICT for improving VO2max (weighted Hedge's g = -0.004, 95% confidence interval (95%CI): -0.08 to 0.07), the overall unclear risk of bias calls the validity of this conclusion into question. Future studies using robust study designs are needed to interrogate the possibility that SIT and MICT result in similar changes in VO2max.

Effects of High-Intensity Interval Training on Selected Adipokines and Cardiometabolic Risk Markers in Normal-Weight and Overweight/Obese Young Males-A Pre-Post Test Trial

The study aimed to assess effects of high-intensity interval training (HIIT) on plasma adipokines and cardiometabolic markers in normal and excess weight youth. Eighteen healthy young males (18.2 ± 1.06 yrs.) were divided in normal-weight group (NWG; body mass index (BMI), 20.5 ± 1.51 kg/m2; n = 9) and excess-weight group (EWG; BMI, 30.8 ± 4.56 kg/m2; n = 9). Participants performed an eight-week HIIT program without caloric restriction. Body composition, plasma leptin, adiponectin, chemerin, omentin-1, lipids, C-reactive protein (CRP), and the homeostasis model assessment index for insulin resistance (HOMA-IR) were assessed before and after the HIIT program. The program resulted in significant increases in omentin levels (p < 0.01) in EWG (27%) and NWG (22%), but no changes in leptin, adiponectin, and chemerin in both groups. BMI (−1.62%; p = 0.015), body fat (−1.59%; p = 0.021), total cholesterol (−11.8%; p = 0.026), triglycerides (−21.3%; p = 0.023), and HOMA-IR (−31.5%; p = 0.043) decreased in EWG only. Repeated measures detected significant interaction “Time x Group” for body mass and BMI only. Eight-week HIIT program improved body composition, lipid profile, and insulin sensitivity in excess-weight individuals. It resulted in an increase in omentin levels in both normal- and excess-weight groups, but no changes in leptin, adiponectin, and chemerin. Body composition has not influenced the response of the four adipokines to HIIT.

Psychological Adaptations to High-Intensity Interval Training in Overweight and Obese Adults: A Topical Review

Regular exercise has been reported as a fundamental piece of the management and treatment puzzle of obesity, playing a vital role in numerous psychological indicators. However, it is unclear whether high-intensity interval training (HIIT) can improve critical psychological health markers such as adherence, exercise enjoyment, affective responses, health-related quality of life, anxiety, and depression in overweight and obese adults. The purpose of this topical review was to catalogue studies investigating the psychological responses to HIIT in order to identify what psychological outcomes have been assessed, the research methods used, and the results. The inclusion/exclusion criteria were met by 25 published articles investigating either a traditional, single-component (84%) or a hybrid-type, multi-component (16%) HIIT protocol and involving 930 participants with overweight/obesity. The present topical review on HIIT-induced psychological adaptations shows that this popular exercise mode, but also demanding for the masses, can meaningfully increase the vast majority of the selected mental health-related indices. These improvements seem to be equal if not greater than those observed for moderate-intensity continuous training in overweight and obese adults. However, further research is needed in this area, focusing on the potential mechanisms behind positive alterations in various psychological health parameters through larger samples and high-quality randomized controlled trials.

Affective Valence and Enjoyment in High- and Moderate-High Intensity Interval Exercise. The Tromsø Exercise Enjoyment Study

Introduction

Exercise at high intensity may cause lower affective responses toward exercise compared with moderate intensity exercise. We aimed to elucidate affective valence and enjoyment in high- and moderate-high interval exercise.

Methods

Twenty recreationally active participants (9 females, 11 males, age range: 20-51 years) underwent three different treadmill running exercise sessions per week over a 3-week period, in randomized order; (1) CE70: 45 min continuous exercise at 70% of heart rate maximum (HR_max), (2) INT80: 4 × 4 min intervals at 80% of HR_max, (3) INT90: 4 × 4 min intervals at 90% of HR_max. Pre-tests included graded submaximal steady state intensities and a test to exhaustion for determining peak oxygen uptake and HR_max. Affective valence (pleasure/displeasure) was measured before, during and after the sessions using the Feeling Scale (FS). Enjoyment was assessed before and after the sessions applying the Physical Activity Enjoyment Scale (PACES) and during the sessions using the Exercise Enjoyment Scale (EES).

Results

The participants felt lower pleasure (between-sessions effect: p = 0.02, _p η²: 0.13) during INT90 sessions (FS: 1.08, 95% CI: 0.35-1.92) compared with INT80 (FS: 2.35, 95% CI: 1.62-3.08, p = 0.052) and CE70 sessions (FS: 2.45, 95% CI: 1.72-3.18, p = 0.03), with no differences between INT80 and CE70 sessions (p = 1.00). There were higher enjoyment after INT80 sessions (PACES: 101.5, 95% CI: 95.7-107.3) versus CE70 sessions (PACES: 91.3 95% CI: 85.5-97.1, p = 0.046), and no differences between INT90 (PACES: 98.2, 95% CI: 92.4-103.4) and CE70 (p = 0.29) or INT80 (p = 1.00). For enjoyment during exercise, CE70 were perceived more enjoyable, and INT80 and INT90 less enjoyable in week 2 (EES: week x session: p = 0.01, _p η²: 0.11; CE70: 4.3, 95% CI: 3.6-4.9, INT80: 4.6, 95% CI: 3.9-5.2, INT90: 4.0, 95% CI: 3.4-4.7) and 3 (EES: CE70: 4.2, 95% CI: 3.7-4.8, INT80: 4.8, 95% CI: 4.2-5.3, INT90: 4.3, 95% CI: 3.8-4.9) than in week 1 (EES: CE70: 3.5, 95% CI: 3.0-4.0, INT80: 5.0, 95% CI: 4.5-5.5, INT90: 4.5, 95% CI: 4.0-5.0).

Conclusion

The negative affective consequences associated with high intensity interval exercise can be alleviated by keeping the intensity at or around 80% of HR_max while preserving the beneficial enjoyment responses associated with interval exercise.

Physiological Responses to Low-Volume Interval Training in Women

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

Evidence-based vs. social media based high-intensity interval training protocols: Physiological and perceptual responses

OBJECTIVE

High intensity interval training (HIIT) is a time-efficient exercise modality to improve cardiorespiratory fitness, and has recently been popularised by social media influencers. However, little is known regarding acute physiological and perceptual responses to these online protocols compared to HIIT protocols used within research. The aim was to investigate acute physiological, perceptual and motivational responses to two HIIT protocols popular on social media, and compare these to two evidence-based protocols.

METHODS

Twenty-seven recreationally active (>1 exercise session /week) participants (Age: 22±3y, BMI: 24.3±2.4) completed a randomised cross-over study, whereby each participant completed four HIIT protocols, two already established in research (Ergo-60:60 (cycling 10x60s at 100%Wmaxwith 60s rest), BW-60:60 (body-weight exercises 10x60swith 60s rest)) and two promoted on social media (SM-20:10 (body-weight exercises 20x20swith 10s rest) and SM-40:20 (body-weight exercises 15x40s with 20s rest)). Blood lactate, heart rate (HR), feeling scale (FS), felt arousal scale (FSA), enjoyment and perceived competence were measured in response to each protocol.

RESULTS

Significant differences were observed between BW-60:60 and SM-20:10 for the proportion of intervals meeting the ACSM high-intensity exercise criterion (>80% of HRmax) (BW-60:60 93±10%, SM-20:10 74±20%, P = 0.039) and change in lactate (BW-60:60 +7.8±3.7mmol/L, SM-20:10 +5.5±2.6mmol/L, P = 0.001). The percentage of time spent above the criterion HR was also significantly lower in SM-20:10 compared to all other protocols (Ergo-60:60 13.9±4.9min, BW-60:60 13.5±3.5min, SM-40:20 12.1±2.4min, SM-20:10 7.7±3.1, P<0.05). No differences were observed in lowest reported FS between protocols (P = 0.268), but FS decreased linearly throughout Ergo-60:60 and BW-60:60 (first vs. last interval P<0.05), but not in SM-20:10 or SM-40:20 (P>0.05). Enjoyment was higher upon completion of BW-60:60 compared to Ergo-60:60 and SM-40:20 (P<0.05).

CONCLUSIONS

This study shows that HIIT protocols available on social media offer an interesting real-world alternative for promoting exercise participation. Future studies should continue to investigate these highly popular and practical HIIT protocols.

Respiratory and Perceptual Responses to High-Intensity Interval Exercise in Obese Adults

PURPOSE

Although high-intensity interval exercise (HIIE) has emerged as an attractive alternative to continuous exercise (CE), the effects of HIIE on ventilatory constraints and dyspnea on exertion have not been studied in obese adults, and thus, tolerability of HIIE in obese adults is unknown. The purpose of this study was to examine differences in respiratory and perceptual responses between HIIE and CE in nonobese and obese adults.

METHODS

Ten nonobese (5 men; 24.1 ± 6.2 yr; body mass index, 23.0 ± 1.3 kg·m-2) and 10 obese (5 men; 24.2 ± 3.8 yr; body mass index, 37 ± 4.6 kg·m-2) adults participated in this study. Respiratory and perceptual responses were assessed during HIIE (eight 30-s intervals at 80% maximal work rate, with 45-s recovery periods) and two 6-min sessions of CE, completed below and above ventilatory threshold (Vth).

RESULTS

Despite similar work rate, HIIE was completed at a higher relative intensity in obese when compared with nonobese participants (68.8% ± 9.4% vs 58.9% ± 5.6% maximal oxygen uptake, respectively; P = 0.01). Expiratory flow limitation and/or dynamic hyperinflation was present during HIIE in 50% of the obese but in none of the nonobese participants. Ratings of perceived breathlessness were highest during HIIE (5.3 ± 2.4), followed by CEaboveVth (2.5 ± 1.6), and CEbelowVth (0.9 ± 0.7; P < 0.05) in obese participants. Unpleasantness associated with breathlessness was higher in obese (4.2 ± 3.0) when compared with nonobese participants (0.6 ± 1.3; P = 0.005) during HIIE.

CONCLUSIONS

HIIE, when prescribed relative to maximal work rate, is associated with greater ventilatory constraints and dyspnea on exertion when compared with CE in obese adults. CE may be more tolerable when compared with HIIE for obese adults.

Limited cardiopulmonary capacity in patients with liver cirrhosis when compared to healthy subjects

OBJECTIVES

The present study compared cardiorespiratory capacity between cirrhotic patients and healthy subjects.

METHODS

Nineteen cirrhotic patients and 19 healthy subjects, paired by age and gender, participated in the study. Volunteers performed an incremental cardiopulmonary test with a ramp protocol, a ventilatory and metabolic variables were obtained and analyzed. The recovery was analyzed by calculating the time needed for 50% of oxygen consumption (VO2) recovery to occur as the median between the peak of the exercise and the end of recovery on the VO2 curve (T1/2). The VE/VCO2 slope were performed by the linear regression of ventilation (VE) and carbon dioxide production (VCO2) data.

RESULTS

During resting condition, cirrhotic patients presented significantly higher levels of VO2 compared to healthy subjects. The VE/ VO2 and VE/ VCO2 values were significantly higher in the control group at the anaerobic threshold and at the peak of the test compared to cirrhotic patients. Time under effort was significantly higher for healthy subjects.

CONCLUSIONS

Based on these findings, it is possible to conclude that liver cirrhosis can compromise the patients' quality of life, mainly by inducing metabolic alterations which can impair functional capacity and lead to a sedentary lifestyle.

Genome wide association study of response to interval and continuous exercise training: the Predict-HIIT study

BACKGROUND

Low cardiorespiratory fitness (V̇O_2peak) is highly associated with chronic disease and mortality from all causes. Whilst exercise training is recommended in health guidelines to improve V̇O_2peak, there is considerable inter-individual variability in the V̇O_2peak response to the same dose of exercise. Understanding how genetic factors contribute to V̇O_2peak training response may improve personalisation of exercise programs. The aim of this study was to identify genetic variants that are associated with the magnitude of V̇O₂peak response following exercise training.

METHODS

Participant change in objectively measured V̇O₂peak from 18 different interventions was obtained from a multi-centre study (Predict-HIIT). A genome-wide association study was completed (n = 507), and a polygenic predictor score (PPS) was developed using alleles from single nucleotide polymorphisms (SNPs) significantly associated (P < 1 × 10^-5) with the magnitude of V̇O₂peak response. Findings were tested in an independent validation study (n = 39) and compared to previous research.

RESULTS

No variants at the genome-wide significance level were found after adjusting for key covariates (baseline V̇O₂peak_, individual study, principal components which were significantly associated with the trait). A Quantile-Quantile plot indicates there was minor inflation in the study. Twelve novel loci showed a trend of association with V̇O₂peak response that reached suggestive significance (P < 1 × 10^-5). The strongest association was found near the membrane associated guanylate kinase, WW and PDZ domain containing 2 (MAGI2) gene (rs6959961, P = 2.61 × 10^-7). A PPS created from the 12 lead SNPs was unable to predict V̇O₂peak response in a tenfold cross validation, or in an independent (n = 39) validation study (P > 0.1). Significant correlations were found for beta coefficients of variants in the Predict-HIIT (P < 1 × 10^-4) and the validation study (P <  × 10^-6), indicating that general effects of the loci exist, and that with a higher statistical power, more significant genetic associations may become apparent.

CONCLUSIONS

Ongoing research and validation of current and previous findings is needed to determine if genetics does play a large role in V̇O₂peak response variance, and whether genomic predictors for V̇O₂peak response trainability can inform evidence-based clinical practice. Trial registration Australian New Zealand Clinical Trials Registry (ANZCTR), Trial Id: ACTRN12618000501246, Date Registered: 06/04/2018, http://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=374601&isReview=true .

The Effects of 15 or 30 s SIT in Normobaric Hypoxia on Aerobic, Anaerobic Performance and Critical Power

Sprint interval training (SIT) is a concept that has been shown to enhance aerobic-anaerobic training adaptations and induce larger effects in hypoxia. The purpose of this study was to examine the effects of 4 weeks of SIT with 15 or 30 s in hypoxia on aerobic, anaerobic performance and critical power (CP). A total of 32 male team players were divided into four groups: SIT with 15 s at FiO₂: 0.209 (15 N); FiO₂: 0.135 (15 H); SIT with 30 s at FiO₂: 0.209 (30 N); and FiO₂: 0.135 (30 H). VO_2max did not significantly increase, however time-to-exhaustion (TTE) was found to be significantly longer in the post test compared to pre test (p = 0.001) with no difference between groups (p = 0.86). Mean power (MPw.kg) after repeated wingate tests was significantly higher compared to pre training in all groups (p = 0.001) with no difference between groups (p = 0.66). Similarly, CP was increased in all groups with 4 weeks of SIT (p = 0.001) with no difference between groups (p = 0.82). This study showed that 4 weeks of SIT with 15 and 30 s sprint bouts in normoxia or hypoxia did not increased VO_2max in trained athletes. However, anerobic performance and CP can be increased with 4 weeks of SIT both in normoxia or hypoxia with 15 or 30 s of sprint durations.

Review of High-Intensity Interval Training for Cognitive and Mental Health in Youth

PURPOSE

High-intensity interval training (HIIT) has emerged as a time-efficient strategy to improve children's and adolescents' health-related fitness in comparison to traditional training methods. However, little is known regarding the effects on cognitive function and mental health. Therefore, the aim of this systematic review was to evaluate the effect of HIIT on cognitive function (basic information processing, executive function) and mental health (well-being, ill-being) outcomes for children and adolescents.

METHODS

A systematic search was conducted, and studies were eligible if they 1) included a HIIT protocol, 2) examined cognitive function or mental health outcomes, and 3) examined children or adolescents (5-18 yr). Separate meta-analyses were conducted for acute and chronic studies, with potential moderators (i.e., study duration, risk of bias, participant age, cognitive demand, and study population) also explored.

RESULTS

A total of 22 studies were included in the review. In acute studies, small to moderate effects were found for executive function (standardized mean difference [SMD], 0.50, 95% confidence interval [CI], 0.03-0.98; P = 0.038) and affect (SMD, 0.33; 95% CI, 0.05-0.62; P = 0.020), respectively. For chronic studies, small significant effects were found for executive function (SMD, 0.31; 95% CI, 0.15-0.76, P < 0.001), well-being (SMD, 0.22; 95% CI, 0.02-0.41; P = 0.029), and ill-being (SMD, -0.35; 95% CI, -0.68 to -0.03; P = 0.035).

CONCLUSIONS

Our review provides preliminary review evidence suggesting that participation in HIIT can improve cognitive function and mental health in children and adolescents. Because of the small number of studies and large heterogeneity, more high-quality research is needed to confirm these findings.

Changes in VO2max and cardiac output in response to short-term high-intensity interval training in Caucasian and Hispanic young women: A pilot study

Data obtained in primarily Caucasian (C) and African American adults show that ethnicity does not mediate responsiveness to exercise training. It is unknown if Hispanics (H), who face elevated health risks and are less active than C, exhibit a similar response to exercise training. This study compared cardiorespiratory and hemodynamic responses to high intensity interval training (HIIT) between C and H women. Twelve C and ten H women ages 19–35 yr who were non-obese and inactive completed nine sessions of HIIT over a 3 wk period. Maximal oxygen uptake (VO₂max) was assessed twice at baseline during which thoracic impedance was used to evaluate heart rate (HR), stroke volume (SV) and cardiac output (CO). Habitual physical activity was assessed using accelerometry. Results showed a significant main effect of training for VO₂max in C and H (F = 13.97, p = 0.001) and no group by training interaction (p = 0.65). There was a main effect of training for CO and SV in C and H (F = 7.57, p = 0.01; F = 7.16, p = 0.02), yet post hoc analyses revealed significant increases were only exhibited in C. There was a tendency for a group by training interaction for a-VO₂diff (F = 1.32, p = 0.054), and a large effect size was seen in H (d = 1.02). Overall, data show no effect of ethnicity on changes in VO₂max with low-volume HIIT, yet C and H may achieve this outcome differently. Longer studies in similar populations are needed to verify this result.

Hourly staircase sprinting exercise "snacks" improve femoral artery shear patterns but not flow-mediated dilation or cerebrovascular regulation: a pilot study

Healthy males (n = 10; age: 24 ± 4 years; body mass index: 24 ± 2 kg·m^-2) completed 2 randomized conditions separated by ≥48 h involving 6-8.5 h of sitting with ("stair snacks") and without (sedentary) hourly staircase sprint interval exercise (∼14-20 s each). Resting blood flow and shear rates were measured in the femoral artery, internal carotid artery, and vertebral artery (Duplex ultrasound). Flow-mediated dilation (FMD) was quantified as an index of peripheral endothelial function in the femoral artery. Neurovascular coupling (NVC; regional blood flow response to local increases in cerebral metabolism) was assessed in the posterior cerebral artery (transcranial Doppler ultrasound). Femoral artery hemodynamics were higher following the active trial with no change in the sedentary trial, including blood flow (+32 ± 23% vs. -10 ± 28%; P = 0.015 and P = 0.253, respectively), vascular conductance (+32 ± 27% vs. -15 ± 26%; P = 0.012 and P = 0.098, respectively), and mean shear rate (+17 ± 8% vs. -8 ± 28%; P = 0.004 and P = 0.310, respectively). The change in FMD was not different within or between conditions (P = 0.184). Global cerebral blood flow (CBF), conductance, shear patterns, and NVC were not different within or between conditions (all P > 0.05). Overall, exercise "stair snacks" improve femoral artery blood flow and shear patterns but not peripheral (e.g., FMD) or cerebral (e.g., CBF and NVC) vascular function following prolonged sitting. The study was registered at ClinicalTrials.gov (NCT03374436). Novelty: Breaking up 8.5 h of sitting with hourly staircase sprinting exercise "snacks" improves resting femoral artery shear patterns but not FMD. Cerebral blood flow and neurovascular coupling were unaltered following 6 h of sitting with and without hourly exercise breaks.

The effect of exercise intensity on chronic inflammation: A systematic review and meta-analysis

OBJECTIVES

Chronic inflammation is independently associated with the incidence and progression of chronic disease. Exercise has been found to reduce chronic inflammation, however the role of exercise intensity (work rate) is unknown. This review aimed to determine the pooled effect of higher- compared to lower-intensity aerobic and resistance exercise on chronic inflammation in adults.

DESIGN

Systematic review and meta-analysis.

METHODS

Five electronic databases were searched. Intervention trials that assessed the effect of ≥2 different exercise intensities on peripheral markers of chronic inflammation [c-reactive protein (CRP), interleukin (IL)-6, tumour necrosis factor (TNF)-α and IL-10] in adults were included. Random-effect meta-analyses were conducted to calculate the mean difference in change scores between groups [effect size (ES)]. Sub-group analyses were performed to explore the influence of age, chronic disease, body mass index and intervention duration on inflammation heterogeneity.

RESULTS

Of 3952 studies identified, 27 were included. There were no significant effects of exercise intensity on IL-6 (ES=-0.039, 95%CI=-0.353-0.275; p=0.806), TNF-α (ES=0.296, 95%CI=-0.184-0.777; p=0.227) and IL-10 (ES=0.007, 95%CI=-0.904-0.919; p=0.987). A significant pooled ES was observed for higher- versus lower-intensity exercise on CRP concentrations, in studies of middle-aged adults (ES=-0.412, 95%CI=-0.821- -0.004, p=0.048) or interventions >9 weeks in duration (ES=-0.520, 95%CI=-0.882--0.159, p=0.005).

CONCLUSIONS

Exercise intensity did not influence chronic inflammatory response. However, sub-analyses suggest that higher-intensity training may be more efficacious than lower-intensity for middle-aged adults, or when longer duration interventions are implemented (>9 weeks), in the most commonly-reported analyte (CRP).

Pre-operative aerobic exercise on metabolic health and surgical outcomes in patients receiving bariatric surgery: A pilot trial

Objective

Examine if adding aerobic exercise to standard medical care (EX+SC) prior to bariatric surgery improves metabolic health in relation to surgical outcomes.

Methods

Fourteen bariatric patients (age: 42.3±2.5y, BMI: 45.1±2.5 kg/m²) met inclusion criteria and were match-paired to pre-operative SC (n = 7) or EX+SC (n = 7; walking 30min/d, 5d/wk, 65–85% HR_peak) for 30d. A 120min mixed meal tolerance test was performed pre- and post-intervention (~2d prior to surgery) to assess insulin sensitivity (Matsuda Index) and metabolic flexibility (indirect calorimetry). Aerobic fitness (VO₂peak), body composition (BodPod), and adipokines (adiponectin, leptin) were also measured. Omental adipose tissue was collected during surgery to quantify gene expression of adiponectin and leptin, and operating time and length of hospital stay were recorded. ANOVA and Cohen’s d effect size (ES) was used to test group differences.

Results

SC tended to increase percent body fat (P = 0.06) after the intervention compared to EX+SC. Although SC and EX+SC tended to raise insulin sensitivity (P = 0.11), EX+SC enhanced metabolic flexibility (P = 0.01, ES = 1.55), reduced total adiponectin (P = 0.01, ES = 1.54) with no change in HMW adiponectin and decreased the length of hospital stay (P = 0.05) compared to SC. Albeit not statistically significant, EX+SC increased VO₂peak 2.9% compared to a 5.9% decrease with SC (P = 0.24, ES = 0.91). This increased fitness correlated to shorter operating time (r = -0.57, P = 0.03) and length of stay (r = -0.58, P = 0.03). Less omental total adiponectin (r = 0.52, P = 0.09) and leptin (r = 0.58, P = 0.05) expression correlated with shorter operating time, and low leptin expression was linked to shorter length of stay (r = 0.70, P = 0.01), and low leptin expression was linked to shorter length of stay (r = 0.70, P = 0.01).

Conclusion

Adding pre-operative aerobic exercise to standard care may improve surgical outcomes through a fitness and adipose tissue derived mechanism.

Exercise training protects the heart against ischemia-reperfusion injury: A central role for mitochondria?

Ischemic heart disease is one of the main causes of morbidity and mortality worldwide. Physical exercise is an effective lifestyle intervention to reduce the risk factors for cardiovascular disease and also to improve cardiac function and survival in patients with ischemic heart disease. Among the strategies that contribute to reduce heart damages during ischemia and reperfusion, regular physical exercise is efficient both in rodent experimental models and in humans. However, the cellular and molecular mechanisms of the cardioprotective effects of exercise remain unclear. During ischemia and reperfusion, mitochondria are crucial players in cell death, but also in cell survival. Although exercise training can influence mitochondrial function, the consequences on heart sensitivity to ischemic insults remain elusive. In this review, we describe the effects of physical activity on cardiac mitochondria and their potential key role in exercise-induced cardioprotection against ischemia-reperfusion damage. Based on recent scientific data, we discuss the role of different pathways that might help to explain why mitochondria are a key target of exercise-induced cardioprotection.

A low-calorie diet with or without interval exercise training improves adiposopathy in obese women

The objective of this study was to test if a low-calorie diet plus interval exercise (LCD+INT) improves adiposopathy, an endocrine dysfunction, when compared with an energy-deficit-matched LCD in obese women. Subjects (age: 48.2 ± 2.4 years, body mass index: 37.8 ± 1.3 kg/m2) were randomized to a 13-day LCD (n = 12; mixed meals of ∼1200 kcal/day) or LCD+INT (n = 12; 12 sessions of 60 min/day alternating 3 min at 50% and 90% peak heart rate). Exercise was estimated to expend 350 kcal per oxygen uptake-heart rate regression analysis and individuals were refed calories expended to match energy availability between groups. Absolute (post - pre caloric intake) and relative (total daily and exercise energy expenditure relative to calorie intake) energy deficits were calculated. Fitness (peak oxygen uptake) and body composition (BodPod; Cosmed USA Inc.) were measured and a 120-min, 75g oral glucose tolerance test was performed at pre- and post-intervention to assess adiposopathy (i.e., ratio of high molecular weight-adiponectin to leptin) and estimate insulin sensitivity. LCD and LCD+INT had similar absolute (P = 0.55) and relative (P = 0.76) energy deficits. LCD and LCD+INT had similar reductions in fat mass (both P < 0.001), despite LCD inducing greater weight loss (P = 0.02) than LCD+INT. Both treatments improved adiposopathy (P = 0.003) and peripheral insulin sensitivity (P = 0.02). Absolute energy deficit correlated to improved adiposopathy (r = -0.41, P = 0.05), and absolute and relative energy deficits were associated with increased insulin sensitivity (r = -0.47, P = 0.02; and r = -0.40, P = 0.05, respectively), independent of body composition changes and increased peak oxygen uptake. Taken together, LCD, with or without INT, improves adiposopathy in relation to insulin sensitivity in obese women, suggesting that a short-term energy deficit is key for reducing risk of type 2 diabetes.

Acute Demands and Recovery From Common Interval Training Protocols

Elmer, DJ, Barron, EN, and Chavez, JL. Acute demands and recovery from common interval training protocols. J Strength Cond Res XX(X): 000-000, 2019-The definition of interval training is quite broad, with no accepted procedure for classifying protocols with different workloads and work and recovery interval times. In addition, little is known about the differences in training load and recovery from common interval protocols. The purpose of this study was to evaluate the differences in acute physiological demands and perceived difficulty between 3 common interval training protocols and a moderate, continuous exercise session. Eight subjects completed the training sessions on a cycle ergometer in a randomized order, with at least 1 week between sessions: 30-second/4-minute, 1-minute/1-minute, 4-minute/3-minute, and a 45-minute continuous session. Metabolic variables were measured throughout exercise and 30 minutes of recovery. Training impulse (TRIMP), session-RPE, and RPE-training load were also measured. There were significant differences between protocols, including between interval training protocols, for average V[Combining Dot Above]O2 (p < 0.001) and heart rate (HR) (p = 0.02), total O2 consumption (p < 0.001), peak lactate (p < 0.001), TRIMP (p = 0.02), session-RPE (p = 0.01), and RPE-training load (p < 0.001). There were no significant differences between interval training protocols for peak V[Combining Dot Above]O2 or peak HR attained during exercise. There were also no differences in V[Combining Dot Above]O2 or HR after 5 or 30 minutes of recovery. Blood lactate was only significantly higher after 30 minutes of recovery from the 30-second/4-minute compared with the 4-minute/3-minute protocol (p = 0.001) and the 45-minute session (p < 0.001). These findings show a range of differences in acute physiological demands and perceptions from interval training protocols, which should be accounted for when planning training sessions or research studies or when interpreting past research.

Combining supervised run interval training or moderate-intensity continuous training with the diabetes prevention program on clinical outcomes

PURPOSE

The present study was designed to evaluate the 16 weeks diabetes prevention program (DPP) combined with instructed run sprint interval training (INT) or moderate-intensity continuous training (MICT) on glycemic control, body composition, fitness, exercise adherence, and perceived exercise enjoyment in sedentary, adults with prediabetes.

METHODS

Participants completed three weekly supervised sessions of INT (4-10 bouts of 30 s maximal sprints followed by a 4 min active recovery) or MICT (30-60 min at 45-55% HRR) exercise coupled with the DPP for 16 weeks. At baseline, 8 and 16 weeks, participants completed fitness and clinical assessments as well as questionnaires to assess group and time differences.

RESULTS

Twenty-nine study participants (INT n = 17, MICT n = 12) were randomized, however, significantly (p = 0.024) more participants withdrew from the INT (n = 11) than MICT (n = 4) treatment. There was no significant difference between groups in perceived exercise enjoyment, but, the MICT group significantly improved their perceived exercise enjoyment (10.8 ± 14.2; p = 0.021) from baseline to 16 weeks. Both INT and MICT groups decreased their body weight (2.0 ± 0.8 vs. - 5.5 ± 1.4 kg; p < 0.001), BMI (- 0.6 ± 0.3 vs. - 2.1 ± 0.5 kg/m²; p < 0.001), body fat mass (1.4 ± 0.6 vs. - 4.2 ± 1.0 kg; p < 0.001), fasting glucose (- 0.09 ± 0.01 vs. - 0.18 ± 0.02 mmol/L; p = 0.020), and HbA1c (- 0.21 ± 0.09 vs. - 0.12 ± 0.12%; p = 0.001), respectively, however, the MICT had greater reductions (GxT: p ≤ 0.05) in body weight, BMI, and body fat than the INT group.

CONCLUSION

Sixteen weeks of MICT is adhered to better and elicits greater improvements in body composition than INT. Nevertheless, both interventions similarly reduced fasting glucose and HbA1c in adults with prediabetes, suggesting either treatment could be effective for T2D prevention.

Perceptual and Cardiorespiratory Responses to High-Intensity Interval Exercise in Adolescents: Does Work Intensity Matter?

High-intensity interval exercise (HIIE) may not elicit prominent unpleasant feelings even with elevated perceived exertion and physiological stress in adolescents. However, the influence of different HIIE work intensities on the affective experience and cardiorespiratory responses is unknown. This study examined the acute affective, enjoyment, perceived exertion and cardiorespiratory responses to HIIE with different work intensities in adolescents. Participants (n = 16; 8 boys; age 12.0 ± 0.3 years) performed, on separate days, HIIE conditions consisting of 8 x 1-minute work-intervals at 70%, 85%, or 100% peak power separated by 75 seconds recovery at 20 W. Affect, enjoyment and rating of perceived exertion (RPE) were recorded before, during, and after HIIE. Heart rate (HR) and oxygen uptake were collected during HIIE. Affect declined in all conditions (p < 0.01) but 100%HIIE elicited significantly lower affect than 70%HIIE and 85%HIIE at work-interval 8 (all p < 0.02, ES > 1.74; 70%HIIE = 2.5 ± 0.8; 85%HIIE = 1.1 ± 1.5; 100%HIIE = -1.5 ± 1.4 on feeling scale). Similar enjoyment was evident during and after all conditions (all p > 0.44). RPE was significantly higher during 100%HIIE than 70%HIIE and 85%HIIE across all work-intervals (all p < 0.01, ES > 1.56). The majority of the participants attained ≥90%HR_max during 85%HIIE (87%) and 100%HIIE (100%), but not during 70%HIIE (6%). Affect responses during HIIE are dependent on the intensity of the work-interval and are not entirely negative (unpleasant feelings). Despite similar enjoyment, positive affect experienced during 70%HIIE and 85%HIIE could serve as a strategy to encourage exercise adoption and adherence in adolescents, but only 85%HIIE elicits sufficient HR stimulus to facilitate potential health benefits.

A Multi-Center Comparison of O2peak Trainability Between Interval Training and Moderate Intensity Continuous Training

There is heterogeneity in the observed O_2peak response to similar exercise training, and different exercise approaches produce variable degrees of exercise response (trainability). The aim of this study was to combine data from different laboratories to compare O_2peak trainability between various volumes of interval training and Moderate Intensity Continuous Training (MICT). For interval training, volumes were classified by the duration of total interval time. High-volume High Intensity Interval Training (HIIT) included studies that had participants complete more than 15 min of high intensity efforts per session. Low-volume HIIT/Sprint Interval Training (SIT) included studies using less than 15 min of high intensity efforts per session. In total, 677 participants across 18 aerobic exercise training interventions from eight different universities in five countries were included in the analysis. Participants had completed 3 weeks or more of either high-volume HIIT (n = 299), low-volume HIIT/SIT (n = 116), or MICT (n = 262) and were predominately men (n = 495) with a mix of healthy, elderly and clinical populations. Each training intervention improved mean O_2peak at the group level (P < 0.001). After adjusting for covariates, high-volume HIIT had a significantly greater (P < 0.05) absolute O_2peak increase (0.29 L/min) compared to MICT (0.20 L/min) and low-volume HIIT/SIT (0.18 L/min). Adjusted relative O_2peak increase was also significantly greater (P < 0.01) in high-volume HIIT (3.3 ml/kg/min) than MICT (2.4 ml/kg/min) and insignificantly greater (P = 0.09) than low-volume HIIT/SIT (2.5 mL/kg/min). Based on a high threshold for a likely response (technical error of measurement plus the minimal clinically important difference), high-volume HIIT had significantly more (P < 0.01) likely responders (31%) compared to low-volume HIIT/SIT (16%) and MICT (21%). Covariates such as age, sex, the individual study, population group, sessions per week, study duration and the average between pre and post O_2peak explained only 17.3% of the variance in O_2peak trainability. In conclusion, high-volume HIIT had more likely responders to improvements in O_2peak compared to low-volume HIIT/SIT and MICT.

Contribution of central and peripheral adaptations to changes in maximal oxygen uptake following 4 weeks of sprint interval training

The current study examined the contribution of central and peripheral adaptations to changes in maximal oxygen uptake (V̇O_2max) following sprint interval training (SIT). Twenty-three males completed 4 weekly SIT sessions (8 × 20-s cycling bouts at ∼170% of work rate at V̇O_2max, 10-s recovery) for 4 weeks. Following completion of training, the relationship between changes in V̇O_2max and changes in central (cardiac output) and peripheral (arterial-mixed venous oxygen difference (a-vO₂diff), muscle capillary density, oxidative capacity, fibre-type distribution) adaptations was determined in all participants using correlation analysis. Participants were then divided into tertiles on the basis of the magnitude of their individual V̇O_2max responses, and differences in central and peripheral adaptations were examined in the top (HI; ∼10 mL·kg^-1·min^-1 increase in V̇O_2max, p < 0.05) and bottom (LO; no change in V̇O_2max, p > 0.05) tertiles (n = 8 each). Training had no impact on maximal cardiac output, and no differences were observed between the LO group and the HI group (p > 0.05). The a-vO₂diff increased in the HI group only (p < 0.05) and correlated significantly (r = 0.71, p < 0.01) with changes in V̇O_2max across all participants. Muscle capillary density (p < 0.02) and β-hydroxyacyl-CoA dehydrogenase maximal activity (p < 0.05) increased in both groups, with no between-group differences (p > 0.05). Citrate synthase maximal activity (p < 0.01) and type IIA fibre composition (p < 0.05) increased in the LO group only. Collectively, although the heterogeneity in the observed V̇O_2max response following 4 weeks of SIT appears to be attributable to individual differences in systemic vascular and/or muscular adaptations, the markers examined in the current study were unable to explain the divergent V̇O_2max responses in the LO and HI groups.

Effects of high-intensity interval training frequency on perceptual responses and future physical activity participation

The effectiveness of high-intensity interval training (HIIT) in inducing positive physiological adaptations is well documented. However, its impact on perceptual responses and on future physical activity (PA) engagement is less evaluated. The present study aimed to examine the effects of HIIT frequency on perceptual responses, health-related quality of life (HRQOL), and its influence in future PA participation. Thirty-five inactive adults were randomly assigned to a control (CON) and to 2 training groups that performed HIIT (10 × 60 s cycling, ∼83% peak power output) for 2 (HIIT-2) or 3 (HIIT-3) times per week for 8 weeks. Following the HIIT intervention, exercise enjoyment, HRQOL, and the intention to implement HIIT in the future were evaluated. Eight weeks after cessation of training, follow-up evaluations of HRQOL and PA were performed. Following the intervention, both training frequencies induced high levels of enjoyment (HIIT-2: 6.0 ± 1.1, HIIT-3: 6.0 ± 1.1, scale 1-7), improved HRQOL (HIIT-2: p = 0.040; HIIT-3: p = 0.024), and reported intention to implement HIIT in the future (HIIT-3: 100%, HIIT-2: 93% of participants). At follow-up, HIIT-3 participants reported higher completion of HIIT compared with HIIT-2 and CON (p < 0.05). Both training groups sustained improved HRQOL and increased vigorous and total PA (p < 0.05). This study showed that performing HIIT either 2 or 3 times per week is an enjoyable exercise modality that promotes a sustainable increase in habitual PA levels and improves HRQOL. Moreover, the higher training frequency resulted in greater HIIT completion in the 8-week period following the cessation of training.

The influence of high-intensity interval training on anthropometric variables of adults with overweight or obesity: a systematic review and network meta-analysis

OBJECTIVE

The goal of this study was to evaluate the influence of high-intensity interval training (HIIT) on anthropometric variables in adults afflicted with overweight or obesity and to compare the effects with those of moderate-intensity continuous training.

METHODS

A computer literature search was performed for HIIT intervention studies that evaluated anthropometric variables in adults afflicted with overweight or obesity.

RESULTS

Of the 857 articles retrieved in the electronic search, 48 met the inclusion criteria. The analyses demonstrated that HIIT was effective in decreasing body mass (-1.45 kg [95% CI: -1.85 to -1.05 kg]), body mass index (-0.44 kg m^-2 [95% CI: -0.59 to -0.30 kg m^-2 ]), waist circumference (-2.3 cm [95% CI: -3.1 to -1.4 cm]), waist/hip ratio (-0.01 [95% CI: -0.02 to -0.00]), body fat percentage (-1.29% [95% CI: -1.70% to -0.87%]) and abdominal visceral fat area (-6.83 cm² [95% CI: -11.95 to -1.71 cm² ]). When considering equalization between the two methods (energy expenditure or workload matched), no differences were found in any measure except body mass (for which HIIT was superior).

CONCLUSIONS

High-intensity interval training and moderate-intensity continuous training results were similar, particularly when equalization between the two methods was considered. Thus, HIIT can be used as a secondary method for the treatment of obesity in adults.

High-Intensity Interval Training Improves Markers of Oxidative Metabolism in Skeletal Muscle of Individuals With Obesity and Insulin Resistance

Background: The excess body fat characteristic of obesity is related to various metabolic alterations, which includes insulin resistance (IR). Among the non-pharmacological measures used to improve insulin sensitivity are aerobic physical training, such as high-intensity interval training (HIIT). This study investigated the effects of 8 weeks of HIIT on blood and skeletal muscle markers related to IR and oxidative metabolism in physically inactive individuals with obesity and compared the changes between insulin resistant and non-insulin resistant phenotypes.

Methods: Initially to investigate the effect of obesity and IR in the analyzed parameters, insulin-sensitive eutrophic volunteers (CON; n = 9) and obese non-insulin (OB; n = 9) and insulin-resistant (OBR; n = 8) were enrolled. Volunteers with obesity completed 8 weeks of HIIT in a cycle ergometer. Venous blood and vastus lateralis muscle samples were obtained before and after the HIIT. Body composition and peak oxygen consumption (VO₂peak) were estimated before and after HIIT.

Results: HIIT reduced IR assessed by the homeostatic model assessment of insulin resistance (HOMA-IR) in OBR (4.4 ± 1.4 versus 4.1 ± 2.2 μU L⁻²), but not in OB (HOMA-IR 1.8 ± 0.5 versus 2.3 ± 1.0 μU L⁻²) volunteers. HIIT increased VO₂peak with no change in body fat in both groups. In skeletal muscle, HIIT increased the phosphorylation of IRS (Tyr612), Akt (Ser473), and increased protein content of β-HAD and COX-IV in both groups. There was a reduction in ERK1/2 phosphorylation in OBR after HIIT.

Conclusion: Eight weeks of HIIT increased the content of proteins related to oxidative metabolism in skeletal muscle of individuals with obesity, independent of changes total body fat.

Glucose Tolerance is Linked to Postprandial Fuel Use Independent of Exercise Dose

PURPOSE

The optimal short-term exercise dose to improve glucose tolerance in relation to metabolic flexibility and/or insulin resistance is unknown. Therefore, we tested if short-term, work-matched continuous (CONT) versus interval (INT) exercise training improves glucose tolerance in part by reducing insulin resistance and increasing metabolic flexibility independent of clinically meaningful fat loss in adults with prediabetes.

METHODS

Subjects (age = 60.9 ± 1.4 yr, body mass index = 33.5 ± 1.1 kg·m) were screened for prediabetes using the American Diabetes Association criteria (75 g oral glucose tolerance test [OGTT] and/or HbA1c) and were randomized to 60 min·d of supervised CONT (n = 17, 70% HRpeak) or work-matched INT (n = 14; 90% HRpeak for 3 min and 50% HRpeak for 3 min) exercise for 12 bouts. Fitness (V˙O2peak) and body composition were assessed pre- and postintervention. A 180-min 75-g OGTT was performed, and glucose, insulin, and free fatty acids were collected to calculate glucose tolerance (tAUC180min) and whole-body as well as adipose tissue insulin resistance pre- and postintervention. RER (indirect calorimetry) was also measured at 0, 60, 120, and 180 min of the OGTT to assess fasting and postprandial metabolic flexibility.

RESULTS

CONT and INT training improved V˙O2peak (L·min; P = 0.001) and glucose tolerance (P = 0.01) and reduced fasting RER (P = 0.006), as well as whole-body and adipose insulin resistance (both P = 0.02) with no effect on body fat (P = 0.18). Increased postprandial RER was correlated with reduced glucose tAUC180min (r = -0.38, P = 0.05) and increased 180-min RER related to decreased whole-body insulin resistance (r = -0.42, P = 0.03).

CONCLUSION

Independent of exercise dose and fat loss, short-term training improves glucose tolerance in relation to enhanced postprandial fuel use.

High-Intensity Interval Training Combined With Vibration and Dietary Restriction Improves Body Composition and Blood Lipids in Obese Adults: A Randomized Trial

This study aimed to compare the effect of high-intensity interval training (HIIT) with additional whole-body vibration (WBV) on body composition and lipid profile in obese/overweight adults on a hypocaloric diet. Forty adults were randomly assigned to (a) HIIT and vibration and hypocaloric diet (HIITWBV, n = 13), (b) HIIT and diet (HIIT, n = 14), and (c) diet only (control [CON], n = 13). High-intensity interval training WBV participants trained 3 times per week for 8 weeks (6 sets × 1 minute of HIIT, cycling at 90% heart rate peak followed by 1 minute of interset vibration, at a frequency of 18 Hz increasing until 25 Hz with a peak-to-peak displacement of 4 mm. Training volume increased 1 set every 2 weeks until 10 sets). The HIIT group performed HIIT training followed by 2 minutes of passive recovery, while the CON continued with their daily activities combined with calorie restriction. Body composition (body fat and fat-free mass) and biochemical indices (glucose, total cholesterol, high-density lipoprotein cholesterol, and triglycerides) were determined. Following 8 weeks, body fat was significantly reduced by 7.5% and both triglycerides and total cholesterol decreased in the HIITWBV group only (−16.5% and −11.7% respectively). This study suggests that HIIT in combination with WBV and a hypocaloric diet can improve overall lipid profile in overweight/obese individuals.

Change in VO2max and time trial performance in response to high-intensity interval training prescribed using ventilatory threshold

Completion of high-intensity interval training (HIIT) leads to significant increases in maximal oxygen uptake (VO_2max) and oxidative capacity. However, individual responses to HIIT have been identified as approximately 20-40% of individuals show no change in VO_2max, which may be due to the relatively homogeneous approach to implementing HIIT.

PURPOSE

This study tested the effects of HIIT prescribed using ventilatory threshold (VT) on changes in VO_2max and cycling performance.

METHODS

Fourteen active men and women (age and VO_2max = 27 ± 8 year and 38 ± 4 mL/kg/min) underwent nine sessions of HIIT, and 14 additional men and women (age and VO_2max = 22 ± 3 year and 40 ± 5 mL/kg/min) served as controls. Training was performed on a cycle ergometer at a work rate equal to 130%VT and consisted of eight to ten 1 min bouts interspersed with 75 s of recovery. At baseline and post-testing, they completed progressive cycling to exhaustion to determine VO_2max, and on a separate day, a 5 mile cycling time trial.

RESULTS

Compared to the control group, HIIT led to significant increases in VO_2max (6%, p = 0.007), cycling performance (2.5%, p = 0.003), and absolute VT (9 W, p = 0.005). However, only 57% of participants revealed meaningful increases in VO_2max and cycling performance in response to training, and two showed no change in either outcome.

CONCLUSIONS

A greater volume of HIIT may be needed to maximize the training response for all individuals.

High intensity interval training is associated with greater impact on physical fitness, insulin sensitivity and muscle mitochondrial content in males with overweight/obesity, as opposed to continuous endurance training: a randomized controlled trial

OBJECTIVES

To evaluate the effect of high intensity training (HIT) on physical fitness, basal respiratory exchange ratio (bRER), insulin sensitivity and muscle histology in overweight/obese men compared to continuous aerobic training (CAT).

MATERIAL AND METHODS

16 male participants with overweight/obesity (age: 42-57 years, body mass index: 28-36 kg/m2) were randomized to HIT (n=8) or CAT (n=8) for 10 weeks, twice a week. HIT was composed of 10 minutes high intensity, 10 minutes continuous aerobic, 10 minutes high intensity exercises. CAT was composed of three times 10 minutes continuous exercising. Changes in anthropometry, physical and metabolic fitness were evaluated. Muscle histology (mitochondria and lipid content) was evaluated by transmission electron microscopy (TEM).

RESULTS

HIT showed a significant increase for peak VO2 (P=0.01), for insulin sensitivity (AUC glucose (P<0,001), AUC insulin (P<0,001), OGTT composite score (P=0.007)) and a significant decrease of bRER (P<0.001) compared to CAT. Muscle mitochondrial content was significantly increased after HIT at the subsarcolemmal (P=0.004 number and P=0.001 surface) as well as the intermyofibrillar site (P<0.001 number and P=0.001 surface).

CONCLUSION

High intensity training elicits stronger beneficial effects on physical fitness, basal RER, insulin sensitivity, and muscle mitochondrial content, as compared to continuous aerobic training.

A scoping review of the psychological responses to interval exercise: is interval exercise a viable alternative to traditional exercise?

While considerable evidence suggests that interval exercise confers numerous physiological adaptations linked to improved health, its psychological consequences and behavioural implications are less clear and the subject of intense debate. The purpose of this scoping review was to catalogue studies investigating the psychological responses to interval exercise in order to identify what psychological outcomes have been assessed, the research methods used, and the results. A secondary objective was to identify research issues and gaps. Forty-two published articles met the review inclusion/exclusion criteria. These studies involved 1258 participants drawn from various active/inactive and healthy/unhealthy populations, and 55 interval exercise protocols (69% high-intensity interval training [HIIT], 27% sprint interval training [SIT], and 4% body-weight interval training [BWIT]). Affect and enjoyment were the most frequently studied psychological outcomes. Post-exercise assessments indicate that overall, enjoyment of, and preferences for interval exercise are equal or greater than for continuous exercise, and participants can hold relatively positive social cognitions regarding interval exercise. Although several methodological issues (e.g., inconsistent use of terminology, measures and protocols) and gaps (e.g., data on adherence and real-world protocols) require attention, from a psychological perspective, the emerging data support the viability of interval exercise as an alternative to continuous exercise.

Potential Universal Application of High-intensity Interval Training from Athletes and Sports Lovers to Patients

Recently, high-intensity interval training (HIIT) has received much attention as a promising exercise option not only to improve aerobic fitness, but also to prevent and improve lifestyle-related diseases. Epidemiological studies have shown that the exercise volume, as determined by the product of exercise intensity, duration, and frequency, has been shown to be important for improvements in muscle mitochondrial activity and subsequent improvements in aerobic fitness, insulin sensitivity, and metabolic variables. Therefore, continuous moderate-intensity training has been widely recommended. On the other hand, the main contributor of HIIT to improvements in aerobic fitness and metabolic variables is its high-intensity nature, and many recent studies have shown results favoring HIIT when compared with conventional continuous training, despite its shorter exercise duration and smaller exercise volume. In this review, we aim to show the possible universal application of HIIT in a hospital setting, where athletes, sports lovers, and patients have sought medical advice and have the opportunity to undergo detailed evaluations, including an exercise stress test. For athletes, HIIT is mandatory to achieve further improvements in aerobic fitness. For patients, though higher levels of motivation and careful evaluation are required, the time constraints of HIIT are smaller and both aerobic and resistance training can be expected to yield favorable results because of the high-intensity nature of HIIT.

The impact of work-matched interval training on V̇O2peak and V̇O2 kinetics: diminishing returns with increasing intensity

High-intensity interval training (HIIT) improves peak oxygen uptake (V̇O2peak) and oxygen uptake (V̇O2) kinetics, however, it is unknown whether an optimal intensity of HIIT exists for eliciting improvements in these measures of whole-body oxidative metabolism. The purpose of this study was to (i) investigate the effect of interval intensity on training-induced adaptations in V̇O2peak and V̇O2 kinetics, and (ii) examine the impact of interval intensity on the frequency of nonresponders in V̇O2peak. Thirty-six healthy men and women completed 3 weeks of cycle ergometer HIIT, consisting of intervals targeting 80% (LO), 115% (MID), or 150% (HI) of peak aerobic power. Total work performed per training session was matched across groups. A main effect of training (p < 0.05) and a significant interaction effect was observed for V̇O2peak, with the change in V̇O2peak being greater (p < 0.05) in the MID group than the LO group; however, no differences were observed between the HI group and either the MID or LO groups (ΔV̇O2peak; LO, 2.7 ± 0.7 mL·kg–1·min–1; MID, 5.8 ± 0.7; HI, 4.2 ± 1.0). The greatest proportion of responders was observed in the MID group (LO, 8/12; MID, 12/13; HI, 9/11). A nonsignificant relationship (p = 0.26; r2 = 0.04) was found between the changes in V̇O2peak and τV̇O2. These results suggest that training at intensities around V̇O2peak may represent a threshold intensity above which further increases in training intensity provide no additional adaptive benefit. The dissociation between changes in V̇O2peak and V̇O2 kinetics also reflects the different underlying mechanisms regulating these adaptations.

The Effect of Training Intensity on VO2max in Young Healthy Adults: A Meta-Regression and Meta-Analysis

Exercise training at a variety of intensities increases maximal oxygen uptake (VO₂max), the strongest predictor of cardiovascular and all-cause mortality. The purpose of the present study was to perform a systematic review, meta-regression and meta-analysis of available literature to determine if a dose-response relationship exists between exercise intensity and training-induced increases in VO₂max in young healthy adults. Twenty-eight studies involving human participants (Mean age: 23±1 yr; Mean VO₂max: 3.4±0.8 l·min^-1) were included in the meta-regression with exercise training intensity, session dose, baseline VO₂max, and total training volume used as covariates. These studies were also divided into 3 tertiles based on intensity (tertile 1: ~60-70%; 2: ~80-92.5%; 3: ~100-250%VO₂max), for comparison using separate meta-analyses. The fixed and random effects meta-regression models examining training intensity, session dose, baseline VO₂max and total training volume was non-significant (Q4=1.36; p=0.85; R²=0.05). There was no significant difference between tertiles in mean change in VO₂max (tertile 1:+0.29±0.15 l/min, ES (effect size) =0.77; 2:+0.26±0.10 l/min, ES=0.68; 3:+0.35±0.17 l/min, ES=0.80), despite significant (p<0.05) reductions in session dose and total training volume as training intensity increased. These data suggest that exercise training intensity has no effect on the magnitude of training-induced increases in maximal oxygen uptake in young healthy human participants, but similar adaptations can be achieved in low training doses at higher exercise intensities than higher training doses of lower intensity (endurance training).

Interleukin-6 and associated cytokine responses to an acute bout of high-intensity interval exercise: the effect of exercise intensity and volume

Acute increases in interleukin (IL)-6 following prolonged exercise are associated with the induction of a transient anti-inflammatory state (e.g., increases in IL-10) that is partly responsible for the health benefits of regular exercise. The purposes of this study were to investigate the IL-6-related inflammatory response to high-intensity interval exercise (HIIE) and to determine the impact of exercise intensity and volume on this response. Ten participants (5 males and 5 females) completed 3 exercise bouts of contrasting intensity and volume (LOW, MOD, and HIGH). The HIGH protocol was based upon standard HIIE protocols, while the MOD and LOW protocols were designed to enable a comparison of exercise intensity and volume with a fixed duration. Inflammatory cytokine concentrations were measured in plasma (IL-6, IL-10) and also determined the level of gene expression (IL-6, IL-10, and IL-4R) in peripheral blood. The plasma IL-6 response to exercise (reported as fold changes) was significantly greater in HIGH (2.70 ± 1.51) than LOW (1.40 ± 0.32) (P = 0.04) and was also positively correlated to the mean exercise oxygen uptake (r = 0.54, P < 0.01). However, there was no change in anti-inflammatory IL-10 or IL-4R responses in plasma or at the level of gene expression. HIIE caused a significant increase in IL-6 and was greater than that seen in low-intensity exercise of the same duration. The increases in IL-6 were relatively small in magnitude, and appear to have been insufficient to induce the acute systemic anti-inflammatory effects, which are evident following longer duration exercise.

Effects of high-intensity interval training on cardiometabolic risk factors in overweight/obese women

The purpose of this study was to evaluate two practical interval training protocols on cardiorespiratory fitness, lipids and body composition in overweight/obese women. Thirty women (mean ± SD; weight: 88.1 ± 15.9 kg; BMI: 32.0 ± 6.0 kg · m(2)) were randomly assigned to ten 1-min high-intensity intervals (90%VO2 peak, 1 min recovery) or five 2-min high-intensity intervals (80-100% VO2 peak, 1 min recovery) or control. Peak oxygen uptake (VO2 peak), peak power output (PPO), body composition and fasting blood lipids were evaluated before and after 3 weeks of training, completed 3 days per week. Results from ANCOVA analyses demonstrated no significant training group differences for any primary variables (P > 0.05). When training groups were collapsed, 1MIN and 2MIN resulted in a significant increase in PPO (∆18.9 ± 8.5 watts; P = 0.014) and time to exhaustion (∆55.1 ± 16.4 s; P = 0.001); non-significant increase in VO2 peak (∆2.36 ± 1.34 ml · kg(-)(1) · min(-)(1); P = 0.185); and a significant decrease in fat mass (FM) (-∆1.96 ± 0.99 kg; P = 0.011). Short-term interval exercise training may be effective for decreasing FM and improving exercise tolerance in overweight and obese women.