Comparison of Three Popular Exercise Modalities on V˙O2max in Overweight and Obese

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

REGISTRATION

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

Classifying Intensity Domains From Arm Cycle Ergometry Differs Versus Leg Cycling Ergometry

ABSTRACT

Astorino, TA, Robson, T, and McMillan, DW. Classifying intensity domains from arm cycle ergometry differs versus leg cycling ergometry. J Strength Cond Res 37(11): 2192-2199, 2023-This study compared the distribution of exercise intensity domains in response to progressive leg cycle ergometry (LCE) and arm cycle ergometry (ACE). Seventeen active men and women (age and body fat = 26 ± 7 years and 18 ± 3%) initially performed graded exercise on each modality to assess maximal oxygen uptake (V̇o2max) and peak power output (PPO). Using a randomized crossover design, they subsequently performed moderate intensity continuous exercise consisting of three 15-minute bouts at 20, 40, and 60% PPO on each modality. Gas exchange data (V̇o2, V̇co2, and VE), respiratory exchange ratio, heart rate (HR), blood lactate concentration (BLa), and perceptual responses were acquired. Only 2 subjects were classified in the same intensity domains across modalities, with LCE eliciting more subjects exercising at "vigorous" and "near-maximal" intensities than ACE. Time spent above 70 (22 ± 7 vs. 15 ± 8 minutes, d = 1.03) and 80 %HRmax (15 ± 6 vs. 9 ± 6 minutes, d = 1.04) was significantly greater with LCE vs. ACE. Compared with ACE, LCE revealed significantly higher (p < 0.05) peak (94 ± 6 vs. 88 ± 9 %HRmax, d = 0.81) and mean HR (73 ± 6 vs. 66 ± 6 %HRmax, d = 1.20), V̇o2 (54 ± 5 vs. 50 ± 7 %V̇o2max, d = 0.68), and BLa (5.5 ± 2.0 vs. 4.7 ± 1.5 mM, d = 0.48). The results exhibit that progressive leg cycling at identical intensities elicits a greater cardiometabolic stimulus than ACE.

Effects of high-intensity interval training on vascular function in patients with cardiovascular disease: a systematic review and meta-analysis

Background: Exercise training improves endothelial function in patients with cardiovascular disease (CVD). However, the influence of training variables remains unclear. The aim of this study was to evaluate the effect of high-intensity interval training (HIIT), compared to moderate intensity training (MIT) and other exercise modalities (i.e., resistance and combined exercise), on endothelial function, assessed by arterial flow-mediated dilation (FMD) or endothelial progenitor cells (EPCs), in patients with CVD. Secondly, we investigated the influence of other training variables (i.e., HIIT protocol). Methods: The PICOS strategy was used to identify randomised and non-randomised studies comparing the effect of HIIT and other exercise modalities (e.g., MIT) on endothelial function in patients with CVD. Electronic searches were carried out in Pubmed, Embase, and Web of Science up to November 2022. The TESTEX scale was used to evaluate the methodological quality of the included studies. Random-effects models of between-group mean difference (MD) were estimated. A positive MD indicated an effect in favour of HIIT. Heterogeneity analyses were performed by the chi-square test and I 2 index. Subgroup analyses evaluated the influence of potential moderator variables. Results: Fourteen studies (13; 92.9% randomised) were included. Most of the studies trained 3 days a week for 12 weeks and performed long HIIT. No statistically significant differences were found between HIIT and MIT for improving brachial FMD in patients with coronary artery disease (CAD) and heart failure with reduced ejection fraction (HFrEF) (8 studies; MD+ = 0.91% [95% confidence interval (CI) = -0.06, 1.88]). However, subgroup analyses showed that long HIIT (i.e., > 1 min) is better than MIT for enhancing FMD (5 studies; MD+ = 1.46% [95% CI = 0.35, 2.57]), while no differences were found between short HIIT (i.e., ≤ 1 min) and MIT (3 studies; MD+ = -0.41% [95% CI = -1.64, 0.82]). Insufficient data prevented pooled analysis for EPCs, and individual studies failed to find statistically significant differences (p > .050) between HIIT and other exercise modalities in increasing EPCs. Discussion: Poor methodological quality could limit the precision of the current results and increase the inconsistency. Long HIIT is superior to MIT for improving FMD in patients with CAD or HFrEF. Future studies comparing HIIT to other exercise modalities, as well as the effect on EPCs and in HF with preserved ejection fraction are required. Systematic Review Registration: https://www.crd.york.ac.uk/PROSPERO/#myprospero, identifier CRD42022358156.

Human skeletal muscle mitochondrial responses to single-leg intermittent or continuous cycle exercise training matched for absolute intensity and total work

There is renewed interest in the potential for interval (INT) training to increase skeletal muscle mitochondrial content including whether the response differs from continuous (CONT) training. Comparisons of INT and CONT exercise are impacted by the manner in which protocols are "matched", particularly with respect to exercise intensity, as well as inter-individual differences in training responses. We employed single-leg cycling to facilitate a within-participant design and test the hypothesis that short-term INT training would elicit a greater increase in mitochondrial content than work- and intensity-matched CONT training. Ten young healthy adults (five males and five females) completed 12 training sessions over 4 weeks with each leg. Legs were randomly assigned to complete either 30 min of CONT exercise at a challenging sustainable workload (~50% single-leg peak power output; Wpeak) or INT exercise that involved 10 × 3-min bouts at the same absolute workload. INT bouts were interspersed with 1 min of recovery at 10% Wpeak and each CONT session ended with 10 min at 10% Wpeak. Absolute and mean intensity, total training time, and volume were thus matched between legs but the pattern of exercise differed. Contrary to our hypothesis, biomarkers of mitochondrial content including citrate synthase maximal activity, mitochondrial protein content and subsarcolemmal mitochondrial volume increased after CONT (p < 0.05) but not INT training. Both training modes increased single-leg Wpeak (p < 0.01) and time to exhaustion at 70% of single-leg Wpeak (p < 0.01). In a work- and intensity-matched comparison, short-term CONT training increased skeletal muscle mitochondrial content whereas INT training did not.

High-intensity interval training improves the vascular endothelial function comparing moderate-intensity interval training in overweight or obese adults: A meta-analysis

OBJECTIVE

Obesity is associated with endothelial dysfunction and cardiovascular diseases. Moderate-intensity continuous training (MICT) is a common method to improve endothelial function and the cardiovascular risk profile in obesity. However, in recent times, high-intensity interval training (HIIT) has become a popular alternative for MICT primarily because of its time efficiency. Therefore, we hypothesized that HIIT is superior to MICT in improving vascular function. We aimed to evaluate this hypothesis by conducting a meta-analysis and quantifying the effect of HIIT on flow-mediated dilation (FMD) in overweight/obese adults.

METHODS

Databases (Scopus, Web of Science, and PubMed) were searched up to January 2022 for HIIT vs. moderate-intensity interval training (MICT) and HIIT vs. control (CON) studies on endothelial function assessed by flow-mediated dilation (FMD) in overweight and obese adults. From the included studies, standardized mean difference (SMD) and 95% confidence intervals (95% CIs) were calculated.

RESULTS

8 studies with 208 participants were included in this meta-analysis. According to the 6 studies, HIIT improved the FMD with an overall change of %2.6 [(95% CI: 0.82 to 4.377), p = 0.004] compared to the MICT in overweight and obese adults. Moreover, based on the 5 studies that compared HIIT and CON, the results showed HIIT significantly increased FMD by 1.83% [(95% CI: 0.478 to 3.187), p = 0.008].

CONCLUSIONS

These results showed that exercise training, particularly HIIT, could improve endothelial function in overweight and obese adults.

Change in Central Cardiovascular Function in Response to Intense Interval Training: A Systematic Review and Meta-analysis

INTRODUCTION

High-intensity interval training and sprint interval training significantly increase maximal oxygen uptake (V̇O 2max ), which enhances endurance performance and health status. Whether this response is due to increases in central cardiovascular function (cardiac output (CO) and blood volume) or peripheral factors is unknown.

PURPOSE

This study aimed to conduct a systematic review and meta-analysis to assess the effects of high-intensity interval training and sprint interval training (referred to as intense interval training) on changes in central cardiovascular function.

METHODS

We performed a systematic search of eight databases for studies denoting increases in V̇O 2max in which CO, stroke volume (SV), blood volume, plasma volume, end-diastolic/systolic volume, or hematocrit were measured.

RESULTS

Forty-five studies were included in this analysis, comprising 946 men and women of various health status (age and V̇O 2max , 20-76 yr and 13-61 mL·kg -1 ·min -1 ) who performed 6-96 sessions of interval training. Results showed an increase in V̇O 2max with intense interval training that was classified as a large effect ( d = 0.83). SV ( d = 0.69), and CO ( d = 0.49) had moderate effect sizes in response to intense interval training. Of 27 studies in which CO was measured, 77% exhibited significant increases in resting CO or that obtained during exercise. Similarly, 93% of studies revealed significant increases in SV in response to intense interval training. Effect sizes for these outcomes were larger for clinical versus healthy populations. Plasma volume, blood volume, and hematocrit had small effect sizes after training ( d = 0.06-0.14).

CONCLUSIONS

Increases in V̇O 2max demonstrated with intense interval training are attendant with increases in central O 2 delivery with little contribution from changes in hematocrit, blood volume, or plasma volume.

The impact of high-intensity interval training on vascular function in adults: A systematic review and meta-analysis

Aim

We performed a systematic review and meta-analysis to investigate the effects of high-intensity interval training (HIIT) compared with moderate-intensity continuous training (MICT) or with no exercise (CON) on vascular function in adults who were free of cardiometabolic diseases and those with cardiometabolic diseases.

Methods

A search across three electronic databases including Scopus, PubMed, and Web of Science was conducted through February 2022 to identify the randomized trials evaluating HIIT vs. MICT and/or CON on vascular function as measured using brachial artery flow-mediated dilation (FMD) in adults. Separate analyses were conducted for HIIT vs. MICT and/or CON to calculate weighted mean differences (WMD) and 95% confidence intervals (95% CIs) using random or fixed models.

Results

A total of 36 studies involving 1,437 participants who were either free of cardiometabolic diseases or had cardiometabolic diseases were included in the meta-analysis. HIIT effectively increased FMD when compared with MICT [1.59% (95% CI 0.87-2.31), p = 0.001] or CON [3.80% (95% CI 2.58-5.01), p = 0.001]. Subgroup analysis showed that HIIT increased FMD in participants with cardiovascular and metabolic diseases, but not in participants who were free of cardiometabolic diseases. In addition, HIIT effectively increased FMD regardless of age and body mass index.

Conclusion

We confirm that HIIT is effective for improving vascular function in individuals with metabolic disorders and cardiovascular diseases and has a superior effect compared to MICT, demonstrating time efficiency.

Systematic review registration

[https://www.crd.york.ac.uk/prospero], identifier [CRD42022320863].

Effects of the intensity of interval training on aerobic fitness, body composition and resting metabolic rate of women with overweight or obesity: A randomized trial

BACKGROUND: Moderate-intensity interval training (MIIT) may be a viable exercise format for improving body composition, aerobic fitness, and health-related variables. OBJECTIVES: This randomized trial aimed to analyze the effect of MIIT or high-intensity interval training (HIIT) on aerobic fitness, body composition variables, and resting metabolic rate (RMR) in women with overweight or obesity. METHODS: 31 sedentary adult women with overweight or obesity performed 7 weeks × 3 weekly sessions of either HIIT or MIIT. Physical and physiological tests were applied before and after training. RESULTS: In both analyses (intention-to-treat and by adherence to the training), aerobic fitness showed a time effect (p= 0.041 and p= 0.015), but without differences between groups (p> 0.05). No group (HIIT vs. MIIT), time (pre vs. post), or interaction effects (group vs. time) were found for RMR, body composition markers (fat mass, body fat percentage, lean mass), or body mass index – BMI (p> 0.05). In addition, MIIT induced a relatively high drop-out rate. CONCLUSIONS: This study suggested that the short-term (7-weeks) interval exercise training was effective for increasing aerobic fitness, and moderate-intensity intervals were as effective as high-intensity intervals. However, neither training format was effective for changing RMR, body composition variables, or BMI of women with overweight or obesity. Clinical trial ID: RBR-9jd7b7.

Acute Perceptive Responses to 2 Combined Training Methods in Adolescents: A Crossover Study

OBJECTIVE

To compare the acute perceptive responses of different combined training methods in adolescents.

MATERIALS AND METHODS

The sample consisted of 50 adolescents, insufficiently active, aged between 14 and 18 years (58% female). The adolescents performed 2 sessions in a randomized order: moderate-intensity continuous training + resistance training (MICT + RT) and high-intensity interval training + resistance training (HIIT + RT). The rating of perceived exertion, affect, and satisfaction were measured by self-report in 5 moments during the combined training (HIIT or MICT-moments 1, 2, and 3; RT-moments 4 and 5) and 10 minutes after the end of the session.

RESULTS

During HIIT, adolescents reported higher values of rating of perceived exertion compared to the MICT session at moments 2 and 3 in both sexes (P < .05). In addition, at moments 2 and 3 of the HIIT session, female participants were reported to have a higher value of satisfaction compared to MICT (F = 3.953; P = .005; η2 = .067).

CONCLUSION

During the execution of both HIIT + RT and MICT + RT protocols, adolescents showed an increase in the values of pleasure and satisfaction, regardless of sex.

Attenuated Metabolic and Cardiorespiratory Responses to Isoenergetic High-Intensity Interval Exercise of Short Versus Long Bouts

PURPOSE

To compare the metabolic, cardiorespiratory and perceptual responses to three isoenergetic high-intensity interval exercise (HIIE) protocols of different bout duration and an isoenergetic continuous exercise protocol.

METHODS

Eleven healthy males (age, 28 ± 6 yr) performed four 20-min cycling trials of equal mean power output 1 wk apart. Participants cycled either continuously (CON) or intermittently with 10 s (HIIE10), 30 s (HIIE30), or 60 s (HIIE60) bouts at intensities corresponding to 49% (CON) or 100% of power at peak oxygen uptake (V̇O2peak). Recovery intervals during the HIIE trials were 15, 45, and 90 s, respectively.

RESULTS

Average V̇O2 was similar in the HIIE trials (2.29 ± 0.42, 2.20 ± 0.43, and 2.12 ± 0.45 L·min-1, for HIIE10, HIIE30, and HIIE60, respectively), whereas in CON (2.02 ± 0.38 L·min-1), it was lower than HIIE10 (P = 0.002) and HIIE30 (P = 0.043). Average pulmonary ventilation (VE) was higher in HIIE60 compared with HIIE10, HIIE30, and CON (75.8 ± 21.8 L·min-1 vs 64.1 ± 14.5 L·min-1, 64.1 ± 16.2 L·min-1, and 54.0 ± 12.5 L·min-1, respectively, P < 0.001). The peak values and oscillations of V̇O2 and VE in HIIE60 were higher compared with all other trials (P < 0.001). Blood lactate concentration was higher in HIIE60 compared with HIIE10, HIIE30, and CON from the fifth minute onward, reaching 12.5 ± 3.5, 7.2 ± 2.1, 7.9 ± 2.9, and 4.9 ± 1.6 mmol·L-1, respectively, at the end of exercise (P < 0.001). RPE was higher and affective responses were lower in HIIE60 compared with all other trials toward the end of exercise (P < 0.001).

CONCLUSIONS

These findings highlight the importance of bout duration in HIIE, since shorter bouts resulted in attenuated metabolic and cardiorespiratory responses, lower RPE and feelings of displeasure compared with a longer bout, despite equal total work, duration, and work-to-recovery ratio. These results may have implications for the prescription of HIIE in various populations.

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.

Effect of high-intensity interval training protocols on VO2max and HbA1c level in people with type 2 diabetes: A systematic review and meta-analysis

BACKGROUND

The effect of high-intensity interval training (HIIT) protocols according to different work intervals, session volumes and training periods has not been evaluated in patients with type 2 diabetes mellitus (T2DM).

OBJECTIVE

This was a systematic review and meta-analysis of the effect of HIIT and its different protocols compared to moderate-intensity continuous training (MICT) and the control group on VO₂max and glycated hemoglobin (HbA1c) level in patients with T2DM.

METHODS

The search strategy considered studies published up to September 2020 in the databases MEDLINE (PubMed), EMBASE, Cochrane CENTRAL, Web of Science and SPORTDiscus. Two authors independently searched the selected databases for randomized clinical trials that compared HIIT to MICT or the control in adults with T2DM. A random-effects meta-analysis was performed and the data are presented as the mean difference (95% confidence intervals [95% CIs]) between HIIT, MICT and control groups.

RESULTS

A total of 20 studies (738 participants) were included. Overall, HIIT increased VO₂max by 5.09 mL/kg/min (95% CI 2.99; 7.19, I² = 80.89) versus the control and by 1.9 mL/kg/min (95% CI 0.81; 2.98, I² = 25.62) versus MICT. HIIT promoted a significant reduction in HbA1c level of -0.8% (95% CI -1.06; -0.49, I² = 77.31) versus the control but with no difference versus MICT. Moderate-interval, high-volume and long-term training promoted a greater increase in VO₂max. A long interval and moderate volume and period conferred a greater increase in VO₂max versus MICT. A short interval and moderate volume and period conferred a greater reduction in HbA1c level versus the control. No publication bias was detected, as evaluated by a funnel chart and Egger's test (p > 0.05).

CONCLUSIONS

As compared with MICT, HIIT had better effect on VO₂max and a similar effect on HbA1C level. Interval protocols, moderate to long training period and moderate to high volume may maximize the HIIT effect in patients with T2DM.

Effect of Exercise Training on Fat Loss-Energetic Perspectives and the Role of Improved Adipose Tissue Function and Body Fat Distribution

In obesity, excessive abdominal fat, especially the accumulation of visceral adipose tissue (VAT), increases the risk of metabolic disorders, such as type 2 diabetes mellitus (T2DM), cardiovascular disease, and non-alcoholic fatty liver disease. Excessive abdominal fat is associated with adipose tissue dysfunction, leading to systemic low-grade inflammation, fat overflow, ectopic lipid deposition, and reduced insulin sensitivity. Physical activity is recommended for primary prevention and treatment of obesity, T2DM, and related disorders. Achieving a stable reduction in body weight with exercise training alone has not shown promising effects on a population level. Because fat has a high energy content, a large amount of exercise training is required to achieve weight loss. However, even when there is no weight loss, exercise training is an effective method of improving body composition (increased muscle mass and reduced fat) as well as increasing insulin sensitivity and cardiorespiratory fitness. Compared with traditional low-to-moderate-intensity continuous endurance training, high-intensity interval training (HIIT) and sprint interval training (SIT) are more time-efficient as exercise regimens and produce comparable results in reducing total fat mass, as well as improving cardiorespiratory fitness and insulin sensitivity. During high-intensity exercise, carbohydrates are the main source of energy, whereas, with low-intensity exercise, fat becomes the predominant energy source. These observations imply that HIIT and SIT can reduce fat mass during bouts of exercise despite being associated with lower levels of fat oxidation. In this review, we explore the effects of different types of exercise training on energy expenditure and substrate oxidation during physical activity, and discuss the potential effects of exercise training on adipose tissue function and body fat distribution.

Effect of different types of regular exercise on physical fitness in adults with overweight or obesity: Systematic review and meta-analyses

This systematic review examined the effect of exercise training interventions on physical fitness in adults with overweight or obesity and compared the effectiveness of different types of exercise training. Four electronic databases were searched. Articles were included if they described randomized controlled trials of exercise training interventions and their effect on maximal oxygen consumption or muscle strength in adults with overweight or obesity. Changes in outcome parameters were analyzed using random effects meta-analyses for different training types (aerobic, resistance, combined aerobic plus resistance, and high-intensity interval training). Eighty-eight articles satisfied the inclusion criteria of which 66 (3964 participants) could be included in the meta-analyses. All training types increased VO_2max (mean difference 3.82 ml/min/kg (95% CI 3.17, 4.48), P < 0.00001; I² = 48%). In direct comparisons, resistance training was less effective in improving VO_2max than aerobic training, HIIT was slightly more effective than aerobic training, and no difference between aerobic and combined aerobic plus resistance training was found. For muscle strength benefits, incorporation of resistance exercise in the training program is indicated. Exercise training increases VO_2max and muscle strength in adults with overweight or obesity. Differences between training types should be weighed with other needs and preferences when health professionals advise on exercise training to improve physical fitness.

Comparison of High-Intensity Training Versus Moderate-Intensity Continuous Training on Cardiorespiratory Fitness and Body Fat Percentage in Persons With Overweight or Obesity: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND

High-intensity training is comprised of sprint interval training (SIT) and high-intensity interval training (HIIT). This study compared high-intensity training with moderate-intensity continuous training (MICT) on cardiorespiratory fitness (CRF) and body fat percentage for overweight or obese persons.

METHODS

A systematic search of randomized controlled trials using the health science databases occurred up to April, 2020. Twenty-six studies were included for complete analysis. A total of 784 participations were analyzed. The unstandardized mean difference for each outcome measurement was extracted from the studies and pooled with the random effects model.

RESULTS

MICT was significantly better at improving CRF compared with SIT (mean difference = -0.92; 95% confidence interval, -1.63 to -0.21; P = .01; I2 = 10%). Furthermore, there was no significant difference between MICT versus HIIT on CRF (mean difference = -0.52; 95% confidence interval, -1.18 to 0.13; P = .12; I2 = 23%). There was no significant difference in body fat percentage between MICT versus HIIT and MICT versus SIT.

CONCLUSIONS

MICT was significantly better at improving CRF than SIT in overweight or obese persons.

Effectiveness of HIIE versus MICT in Improving Cardiometabolic Risk Factors in Health and Disease: A Meta-analysis

PURPOSE

We aimed to investigate differences between high-intensity interval exercise (HIIE, including high-intensity interval training and sprint interval training) and moderate-intensity continuous training (MICT) on physical fitness, body composition, blood pressure, blood lipids, insulin and glucose metabolism, inflammation, and endothelial function.

METHODS

Differences between HIIE and MICT were summarized using a random-effects meta-analysis on the effect size (Cohen's d). A meta-regression was conducted using the following subgroups: population, age, training duration, men ratio, exercise type, baseline values (clinical relevant ranges), and type of HIIE. Studies were included if at least one of the following outcomes were reported: maximal oxygen uptake (V˙O2max), flow-mediated dilation (FMD), body mass index (BMI), body mass, percent body fat, systolic and diastolic blood pressure, high-density lipoprotein (HDL), low-density lipoprotein (LDL), triglycerides, total cholesterol, C-reactive protein (CRP), fasting glucose and insulin, glycated hemoglobin (HbA1c), and insulin resistance (HOMA-IR). A total of 55 studies were included.

RESULTS

Overall, HIIE was superior to MICT in improving V˙O2max (d = 0.40, P < 0.001) and FMD (d = 0.54, P < 0.05). Oppositely, MICT was superior to HIIE in improving HbA1c (d = -0.27, P < 0.05). No differences were observed in BMI (d = -0.02), body mass (d = -0.05), percent body fat (d = 0.04), systolic blood pressure (d = -0.04), diastolic blood pressure (d = 0.03), HDL (d = -0.05), LDL (d = 0.08), triglycerides (d = 0.03), total cholesterol (d = 0.14), CRP (d = -0.11), fasting insulin (d = 0.02), fasting glucose (d = 0.02), and HOMA-IR (d = -0.04). Moderator analyses indicated that the difference between HIIE and MICT was affected by different subgroups.

CONCLUSION

Overall, HIIE showed to be more effective in improving cardiovascular health and cardiorespiratory fitness, whereas MICT was superior in improving long-term glucose metabolism. In the process of personalized training counseling, health-enhancing effects of exercise training may be improved by considering the individual risk profiles.

HIIT is superior than MICT on cardiometabolic health during training and detraining

PURPOSE

This study investigated the cardiometabolic health of overweight/obese untrained individuals in response to 8 weeks of HIIT and MICT using a field approach, and to 4 weeks of training cessation (TC).

METHODS

Twenty-two subjects performed 8 weeks of moderate intensity continuous training (MICT-n = 11) or high-intensity interval training (HIIT-n = 11) (outdoor running), followed by 4 weeks of TC. Cardiorespiratory fitness, body composition, arterial blood pressure, glucose metabolism and blood lipids were measured pre-training (PRE), post-training (POST) and TC.

RESULTS

HIIT improved eight indicators of cardiometabolic health ([Formula: see text], BMI, body fat, visceral fat, systolic blood pressure, total cholesterol, fasting glucose and triglycerides-p  < 0.05) while MICT only three ([Formula: see text], BMI, and visceral fat-p  < 0.05). After 4 weeks of TC, four positive adaptations from HIIT were negatively affected ( [Formula: see text], visceral fat, systolic blood pressure and total cholesterol-p  < 0.05) and three in the MICT group ([Formula: see text], BMI and visceral fat, p  < 0.05).

CONCLUSION

Eight weeks of HIIT performed in a real-world setting promoted a greater number of positive adaptations in cardiometabolic health of individuals with overweight/obese compared to MICT. Most of the positive effects of the HIIT protocol were also found to be longer lasting and maintained after the suspension of high-intensity interval running for 4 weeks. Conversely, all positive effects of MICT protocols were reversed after TC.

High-Intensity Interval Training versus Moderate-Intensity Continuous Training on Health Outcomes for Children and Adolescents: A Meta-analysis of Randomized Controlled Trials

Low cardiorespiratory fitness (CRF) is considered as an established risk factor for cardiovascular and metabolic disorders. However, the effectiveness of high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) in children and adolescents remained uncertain. Electronic databases of the PubMed, EmBase, and the Cochrane library were searched for randomized controlled trials (RCTs) investigated the role of HIIT versus MICT for children and adolescents throughout December 2019. Sixteen RCTs involving a total of 543 children were selected for final meta-analysis. HIIT versus MICT showed high peak VO2 (weighted mean differences (WMD): 2.68; 95% confidence intervals (CIs): 1.81 to 3.55; $P<0.001$ ), and no evidence of heterogeneity and publication bias was detected. However, there were no significant differences detected between HIIT and MICT on the levels of peak heart rate (HRmax), fat mass, free fat mass, weight, body mass index, waist circumference, systolic blood pressure, diastolic blood pressure, glycemia, insulinemia, total cholesterol, high density lipoprotein, low density lipoprotein, triglycerides, HOMA-IR, HbA1c, and leptinemia. The findings of this study revealed that HIIT versus MICT showed a significant improvement in peak VO2 in children and adolescents. Further large-scale RCTs should be conducted to compare the long-term effects of HIIT versus MICT in children and adolescents.

Characterizing the Heart Rate Response to the 4 × 4 Interval Exercise Protocol

High intensity interval training is frequently implemented using the 4 × 4 protocol where four 4-min bouts are performed at heart rate (HR) between 85 and 95% HR max. This study identified the HR and power output response to the 4 × 4 protocol in 39 active men and women (age and VO₂ max = 26.0 ± 6.1 years and 37.0 ± 5.4 mL/kg/min). Initially, participants completed incremental cycling to assess VO₂ max, HR max, and peak power output (PPO). They subsequently completed the 4 × 4 protocol, during which HR and power output were monitored. Data showed that 12.9 ± 0.4 min of 16 min were spent between 85 and 95% HR max, with time spent significantly lower in interval 1 (2.7 ± 0.6 min) versus intervals 2–4 (3.4 ± 0.4 min, 3.4 ± 0.3 min, and 3.5 ± 0.3 min, d = 2.4–2.7). Power output was highest in interval 1 (75% PPO) and significantly declined in intervals 2–4 (63 to 54% PPO, d = 0.7–1.0). To enhance time spent between 85 and 95% HR max for persons with higher fitness, we recommend immediate allocation of supramaximal intensities in interval one.

Sex Dimorphism of VO2max Trainability: A Systematic Review and Meta-analysis

BACKGROUND

Increases in maximal oxygen uptake (VO_2max) are strongly associated with improved cardiovascular health.

OBJECTIVE

The aim was to perform a systematic review and meta-analysis to determine whether VO_2max responses to endurance training (ET), the most effective intervention to improve VO_2max, are influenced by sex.

METHODS

We conducted a systematic search of MEDLINE and Web of Science since their inceptions until February 2019 for articles assessing the VO_2max response to a given sex-matched dose of ET in healthy age-matched men and women. Meta-analyses were performed to determine the mean difference between VO_2max responses in men versus women. Subgroup and meta-regression analyses were used to assess potential moderating factors.

RESULTS

After systematic review, eight studies met the inclusion criteria. All studies implemented common modalities of ET in healthy untrained individuals, comprising a total of 175 men and women (90 ♂, 85 ♀). ET duration and intensity were sex-matched in all studies. After data pooling, ET induced substantially larger increases in absolute VO_2max in men compared with women (mean difference = + 191 ml·min^-1, 95% CI 99, 283; P < 0.001). A greater effect of ET on relative VO_2max was also observed in men versus women (mean difference = + 1.95 ml·min^-1·kg^-1, 95% CI 0.76, 3.15; P = 0.001). No heterogeneity was detected among studies (I² = 0%, P ≥ 0.59); the meta-analytical results were robust to potential moderating factors.

CONCLUSION

Pooled evidence demonstrates greater improvements in VO_2max in healthy men compared with women in response to a given dose of ET, suggesting the presence of sexual dimorphism in the trainability of aerobic capacity.

The Effects of Short-Term High-Intensity Interval Training and Moderate Intensity Continuous Training on Body Fat Percentage, Abdominal Circumference, BMI and VO2max in Overweight Subjects

We aimed to compare the effects of a personalized short-term high-intensity interval training (HIIT) vs. standard moderate intensity continuous training (MICT) on body fat percentage, abdominal circumference, BMI and maximal oxygen uptake (VO2max) in overweight volunteers. Twenty overweight sedentary volunteers (24.9 ± 2.9y; BMI: 26.1 ± 1 kgm-2) were randomly assigned to 2 groups, HIIT or MICT. HIIT trained 6 weeks (3-days/week), 40-min sessions as follows: 6-min warm-up, 20-min resistance training (RT) at 70% 1-RM, 8-min HIIT up to 90% of the predicted Maximal Heart Rate (HRmax), 6-min cool-down. MICT trained 6 weeks (3-days/week) 60-min sessions as follows: 6-min warm-up, 20-min RT at 70% 1-RM, 30-min MICT at 60-70% of the predicted HRmax, 4-min cool-down. Two-way ANOVA was performed in order to compare the efficacy of HIIT and MICT protocols, and no significant interaction between training x time was evidenced (p > 0.05), indicating similar effects of both protocols on all parameters analyzed. Interestingly, the comparison of Δ mean percentage revealed an improvement in VO2max (p = 0.05) together with a positive trend in the reduction of fat mass percentage (p = 0.06) in HIIT compared to MICT protocol. In conclusion, 6 weeks of personalized HIIT, with reduced training time (40 vs. 60 min)/session and volume of training/week, improved VO2max and reduced fat mass percentage more effectively compared to MICT. These positive results encourage us to test this training in a larger population.

Effectiveness of Aerobic Exercise Programs for Health Promotion in Metabolic Syndrome

PURPOSE

Continuous and interval are the two types of aerobic exercise training commonly used for health promotion. We sought to determine which aerobic exercise training program results in larger health improvements in metabolic syndrome (MetS) individuals.

METHODS

One hundred twenty-one MetS patients (age, 57 ± 8 yr; weight, 92 ± 15 kg; and MetS factors, 3.8 ± 0.8 components) with low initial cardiorespiratory fitness (CRF) (V˙O2peak, 24.0 ± 5.5 mL·kg·min) were randomized to undergo one of the following 16-wk exercise program: (a) 4 × 4-min high-intensity interval training at 90% of HRMAX (4HIIT group; n = 32), (b) 50-min moderate-intensity continuous training at 70% of HRMAX (MICT group; n = 35), (c) 10 × 1-min HIIT at 100% of HRMAX (1HIIT group; n = 32), or (d) no exercise control group (CONT; n = 22). We measured the evolution of all five MetS components (i.e., MetS Z Score) and CRF (assessed by V˙O2peak) before and after intervention.

RESULTS

MetS Z score decreased 41% after 4HIIT (95% confidence interval [CI], 0.25-0.06; P < 0.01) and 52% in MICT (95% CI, 0.24-0.06; P < 0.01), whereas it did not change in 1HIIT (decreased 24%; 95% CI, -0.16 to 0.03; P = 0.21) and CONT (increased 20%; 95% CI, -0.19 to 0.04; P = 0.22). However, the three exercise groups improved similarly their V˙O2peak (4HIIT, 11%; 95% CI, 0.14-0.33; MICT, 12%; 95% CI, 0.18-0.36; and 1HIIT, 14%; 95% CI, 0.21-0.40 L·min; all P < 0.001).

CONCLUSIONS

Our findings suggest that in sedentary individuals with MetS and low initial CRF level any aerobic training program of 16 wk with a frequency of three times per week is sufficient stimulus to raise CRF. However, the more intense but shorter 1HIIT training program is not effective on improving MetS Z score, and thus we caution its recommendation for health promotion purposes in this population.

High intensity interval training and molecular adaptive response of skeletal muscle

Increased cardiovascular fitness, V˙O_2max, is associated with enhanced endurance capacity and a decreased rate of mortality. High intensity interval training (HIIT) is one of the best methods to increase V˙O_2max and endurance capacity for top athletes and for the general public as well. Because of the high intensity of this type of training, the adaptive response is not restricted to Type I fibers, as found for moderate intensity exercise of long duration. Even with a short exercise duration, HIIT can induce activation of AMPK, PGC-1α, SIRT1 and ROS pathway as well as by the modulation of Ca²⁺ homeostasis, leading to enhanced mitochondrial biogenesis, and angiogenesis. The present review summarizes the current knowledge of the adaptive response of HIIT.

High-intensity interval training for health benefits and care of cardiac diseases - The key to an efficient exercise protocol

Aerobic capacity, which is expressed as peak oxygen consumption (VO_2peak), is well-known to be an independent predictor of all-cause mortality and cardiovascular prognosis. This is true even for people with various coronary risk factors and cardiovascular diseases. Although exercise training is the best method to improve VO_2peak, the guidelines of most academic societies recommend 150 or 75 min of moderate- or vigorous- intensity physical activities, respectively, every week to gain health benefits. For general health and primary and secondary cardiovascular prevention, high-intensity interval training (HIIT) has been recognized as an efficient exercise protocol with short exercise sessions. Given the availability of the numerous HIIT protocols, which can be classified into aerobic HIIT and anaerobic HIIT [usually called sprint interval training (SIT)], professionals in health-related fields, including primary physicians and cardiologists, may find it confusing when trying to select an appropriate protocol for their patients. This review describes the classifications of aerobic HIIT and SIT, and their differences in terms of effects, target subjects, adaptability, working mechanisms, and safety. Understanding the HIIT protocols and adopting the correct type for each subject would lead to better improvements in VO_2peak with higher adherence and less risk.

High-Intensity Interval Training in Cardiac Rehabilitation

Recently, high-intensity interval training (HIIT) has been recognized as a safe and effective alternative to moderate-intensity continuous training for older patients with cardiovascular disease (CVD) in cardiac rehabilitation settings in an effort to improve health outcomes. This brief review considers general principles and suggestions for prescription of HIIT for older patients with CVD, specific challenges pertaining to older adults, the physiologic mechanisms by which HIIT contributes to improvements in peak Vo₂, and the effects of HIIT on cardiovascular health in older patients with coronary artery disease and heart failure.

Prevalence and predictors of dropout from high-intensity interval training in sedentary individuals: A meta-analysis

Recent evidence suggests that high-intensity interval training (HIIT) is an effective method to improve fitness and various health markers. However, the tolerability and acceptability of HIIT among sedentary individuals is currently controversially discussed. Therefore, our objective was to investigate the prevalence and predictors of dropout among sedentary individuals in HIIT-based exercise interventions. MEDLINE/PubMed, SPORTDiscus, and Web of Science were searched systematically for relevant articles until 06/2018. Studies included were required to (a) be written in English, (b) include sedentary healthy adults, (c) use some form of HIIT without any complementary intervention, (d) last ≥4 weeks, (e) report detailed description of the applied HIIT protocol, and (f) report data that allow calculation of a dropout rate. Fifty-five studies reporting results from 67 HIIT interventions with 1318 participants met the eligibility criteria. The trim and fill adjusted pooled dropout rate across all interventions was 17.6% (95% confidence interval 14.2-21.5%). Dropout rates were significantly lower in cycling-based interventions compared with studies using running/walking as exercise modality (P < 0.001). Longer session time (β = 0.02, P < 0.05), higher time effort/week (β = 0.005, P < 0.05), and overall time effort/intervention (β = 0.0003, P < 0.05) predicted greater dropout. Exercise intensity was not related to dropout. Our data suggest that HIIT-based interventions are tolerable and acceptable for previously sedentary individuals, exhibiting generally lower dropout rates than commonly reported for traditional exercise programs. Given the association between HIIT volume and dropouts, future studies should further focus on identifying the minimally effective dose of practical HIIT for improving health status. Such efforts would be important to increase implementation and public health impact of HIIT.

Effect of High-Intensity Interval Training versus Moderate-Intensity Continuous Training on Cardiorespiratory Fitness in Children and Adolescents: A Meta-Analysis

Enhancing cardiorespiratory fitness (CRF) can lead to substantial health benefits. Comparisons between high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) on CRF for children and adolescents are inconsistent and inconclusive. The objective of this study was to perform a meta-analysis to compare the effects between HIIT and MICT on CRF in children and adolescents. We searched MEDLINE, PubMed, Web of Science, and Google Scholar to identify relevant articles. The standardized mean differences (SMD) and 95% confidence intervals (95% CI) were calculated to determine the pooled effect size of HIIT and MICT on CRF. A total of 563 subjects from 17 studies (18 effects) were identified. The pooled effect size was 0.51 (95% CI = 0.33-0.69) comparing HIIT to MICT. Moreover, intervention duration, exercise modality, work and rest ratio, and total bouts did not significantly modify the effect of HIIT on CRF. It is concluded that compared with endurance training, HIIT has greater improvements on cardiorespiratory fitness among children and adolescents.

Acute cardiopulmonary responses to strength training, high-intensity interval training and moderate-intensity continuous training

PURPOSE

Long-term effects of exercise training are well studied. Acute hemodynamic responses to various training modalities, in particularly strength training (ST), have only been described in a few studies. This study examines the acute responses to ST, high-intensity interval training (HIIT) and moderate-intensity continuous training (MCT).

METHODS

Twelve young male subjects (age 23.4 ± 2.6 years; BMI 23.7 ± 1.5 kg/m²) performed an incremental exertion test and were randomized into HIIT (4 × 4-min intervals), MCT (continuous cycling) and ST (five body-weight exercises) which were matched for training duration. The cardiopulmonary (impedance cardiography, ergo-spirometry) and metabolic response were monitored.

RESULTS

Similar peak blood lactate responses were observed after HIIT and ST (8.5 ± 2.6 and 8.1 ± 1.2 mmol/l, respectively; p = 0.83). The training impact time was 90.7 ± 8.5% for HIIT and 68.2 ± 8.5% for MCT (p < 0.0001). The mean cardiac output was significantly higher for HIIT compared to that of MCT and ST (23.2 ± 4.1 vs. 20.9 ± 2.9 vs. 12.9 ± 2.9 l/min, respectively; p < 0.0001). VO_2max was twofold higher during HIIT compared to that observed during ST (2529 ± 310 vs. 1290 ± 156 ml; p = 0.0004). Among the components of ST, squats compared with push-ups resulted in different heart rate (111 ± 13.5 vs. 125 ± 15.7 bpm, respectively; p < 0.05) and stroke volume (125 ± 23.3 vs. 104 ± 19.8 ml, respectively; p < 0.05).

CONCLUSIONS

Despite an equal training duration and a similar acute metabolic response, large differences with regard to the training impact time and the cardiopulmonary response give evident. HIIT and MCT, but less ST, induced a sufficient cardiopulmonary response, which is important for the preventive effects of training; however, large differences in intensity were apparent for ST.

Effects of various interval training regimes on changes in maximal oxygen uptake, body composition, and muscular strength in sedentary women with obesity

PURPOSE

We determined the effects of two high-intensity interval training (HIIT) regimens [the traditional (TRAD) and periodized (PER)] on changes in maximal oxygen uptake (VO2max), body composition, and muscular strength in sedentary, obese women.

METHODS

Seventeen women (age and BMI = 37.5 ± 10.5 year and 39.1 ± 4.3 kg/m2) were randomized into a 6 week regime of TRAD or PER which consisted of three sessions per week, two in the laboratory, and one on their own. Pre- and post-training, VO2max, body composition, and muscular strength of the knee extensors (KE) and flexors (KF) were assessed via ramp cycling to exhaustion, air displacement plethysmography, and isokinetic dynamometry, respectively.

RESULTS

VO2max was increased by 4-5% in response to training (p = 0.045) with no group-by-time interaction (p = 0.79). Body mass, fat mass, and waist-to-hip ratio were unaltered (p > 0.05) in response to training, yet there was a significant change in percent body fat (p = 0.03), percent fat-free mass (p = 0.03), and absolute fat-free mass (p = 0.03) in TRAD but not PER. No change occurred in KE (p = 0.36) or KF torque (p = 0.75) in response to training and there was no group-by-time interaction (p > 0.05).

CONCLUSIONS

Low-volume HIIT improved VO2max and body composition but did not modify muscular strength, which suggests that obese women desiring to increase strength should initiate more intense HIIT or partake in formal resistance training.

Effects of different protocols of high intensity interval training for VO2max improvements in adults: A meta-analysis of randomised controlled trials

OBJECTIVES

To examine the effects of different protocols of high-intensity interval training (HIIT) on VO₂max improvements in healthy, overweight/obese and athletic adults, based on the classifications of work intervals, session volumes and training periods.

DESIGN

Systematic review and meta-analysis.

METHODS

PubMed, Scopus, Medline, and Web of Science databases were searched up to April 2018. Inclusion criteria were randomised controlled trials; healthy, overweight/obese or athletic adults; examined pre- and post-training VO₂max/peak; HIIT in comparison to control or moderate intensity continuous training (MICT) groups.

RESULTS

Fifty-three studies met the eligibility criteria. Overall, the degree of change in VO₂max induced by HIIT varied by populations (SMD=0.41-1.81, p<0.05). When compared to control groups, even short-intervals (≤30s), low-volume (≤5min) and short-term HIIT (≤4weeks) elicited clear beneficial effects (SMD=0.79-1.65, p<0.05) on VO₂max/peak. However, long-interval (≥2min), high-volume (≥15min) and moderate to long-term (≥4-12weeks) HIIT displayed significantly larger effects on VO₂max (SMD=0.50-2.48, p<0.05). When compared to MICT, only long-interval (≥2min), high-volume (≥15min) and moderate to long-term (≥4-12weeks) HIIT showed beneficial effects (SMD=0.65-1.07, p<0.05).

CONCLUSIONS

Short-intervals (≤30s), low-volume (≤5min) and short-term (≤4weeks) HIIT represent effective and time-efficient strategies for developing VO₂max, especially for the general population. To maximize the training effects on VO₂max, long-interval (≥2min), high-volume (≥15min) and moderate to long-term (≥4-12weeks) HIIT are recommended.

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.

Short-Term (<8 wk) High-Intensity Interval Training in Diseased Cohorts

BACKGROUND AND AIM

Exercise training regimes can lead to improvements in measures of cardiorespiratory fitness (CRF), improved general health, and reduced morbidity and overall mortality risk. High-intensity interval training (HIIT) offers a time-efficient approach to improve CRF in healthy individuals, but the relative benefits of HIIT compared with traditional training methods are unknown in across different disease cohorts.

METHODS

This systematic review and meta-analysis compares CRF gains in randomized controlled trials of short-term (<8 wk) HIIT versus either no exercise control (CON) or moderate continuous training (MCT) within diseased cohorts. Literature searches of the following databases were performed: MEDLINE, EMBASE, CINAHL, AMED, and PubMed (all from inception to December 1, 2017), with further searches of Clinicaltrials.gov and citations via Google Scholar. Primary outcomes were effect on CRF variables: V˙O2peak and anaerobic threshold.

RESULTS

Thirty-nine studies met the inclusion criteria. HIIT resulted in a clinically significant increase in V˙O2peak compared with CON (mean difference [MD] = 3.32 mL·kg·min, 95% confidence interval [CI] = 2.56-2.08). Overall HIIT provided added benefit to V˙O2peak over MCT (MD = 0.79 mL·kg·min, 95% CI = 0.20-1.39). The benefit of HIIT was most marked in patients with cardiovascular disease when compared with MCT (V˙O2peak: MD = 1.66 mL·kg·min, 95% CI = 0.60-2.73; anaerobic threshold: MD = 1.61 mL·kg·min, 95% CI = 0.33-2.90).

CONCLUSIONS

HIIT elicits improvements in objective measures of CRF within 8 wk in diseased cohorts compared with no intervention. When compared with MCT, HIIT imparts statistically significant additional improvements in measures of CRF, with clinically important additional improvements in V˙O2peak in cardiovascular patients. Comparative efficacy of HIIT versus MCT combined with an often reduced time commitment may warrant HIIT's promotion as a viable clinical exercise intervention.

Effects of low-volume high-intensity interval training in a community setting: a pilot study

PURPOSE

High-intensity interval training (HIIT) is emerging as an effective and time-efficient exercise strategy for health promotion. However, most HIIT studies are conducted in laboratory settings and evidence regarding the efficacy of time-efficient "low-volume" HIIT is based mainly on demanding "all-out" protocols. Thus, the aim of this pilot study was to assess the feasibility and efficacy of two low-volume (≤ 30 min time-effort/week), non-all-out HIIT protocols, performed 2 ×/week over 8 weeks in a community-based fitness centre.

METHODS

Thirty-four sedentary men and women were randomised to either 2 × 4-min HIIT (2 × 4-HIIT) or 5 × 1-min HIIT (5 × 1-HIIT) at 85-95% maximal heart rate (HR_max), or an active control group performing moderate-intensity continuous training (MICT, 76 min/week) at 65-75% HR_max.

RESULTS

The exercise protocols were well tolerated and no adverse events occurred. 2 × 4-HIIT and 5 × 1-HIIT exhibited lower dropout rates (17 and 8 vs. 30%) than MICT. All training modes improved VO_2max (2 × 4-HIIT: + 20%, P < 0.01; 5 × 1-HIIT: + 27%, P < 0.001; MICT: + 16%, P < 0.05), but the HIIT protocols required 60% less time commitment. Both HIIT protocols and MICT had positive impact on cholesterol profiles. Only 5 × 1-HIIT significantly improved waist circumference (P < 0.05) and subjective work ability (P < 0.05).

CONCLUSIONS

The present study indicates that low-volume HIIT can be feasibly implemented in a community-based setting. Moreover, our data suggest that practical (non-all-out) HIIT that requires as little as 30 min/week, either performed as 2 × 4-HIIT or 5 × 1-HIIT, may induce significant improvements in VO_2max and cardiometabolic risk markers.

Influence of a physical exercise program on VO2max in adults with cardiovascular risk factors

OBJECTIVE

The aim of the study was to assess the influence of a physical exercise program on VO₂max in sedentary subjects with cardiovascular risk factors.

MATERIALS AND METHODS

The sample was composed of 214 patients (80 males, 134 females) with an average age of 52 years, who were referred to a physical exercise program from 2 primary care centres of Spanish southeast. It was implemented a 10 week program (3 training×1h/week) combining strength with cardiorespiratory fitness. TheVO₂max was analyzed through the Rockport Walk Test (RWT) comparing the pre and post program measurements.

RESULTS

The results show significant improvements on VO₂max for both genders (p<0,05). The most pronounced increase in VO₂max was among males in the highest age band (56-73 years).

CONCLUSIONS

Prescribing and referral exercise programs from primary care centers must be considered as a resource for improving cardiorespiratory fitness in the population studied.

High-Intensity Interval Training Increases Cardiac Output and V˙O2max

Increases in maximal oxygen uptake (V˙O2max) frequently occur with high-intensity interval training (HIIT), yet the specific adaptation explaining this result remains elusive.

PURPOSE

This study examined changes in V˙O2max and cardiac output (CO) in response to periodized HIIT.

METHODS

Thirty-nine active men and women (mean age and V˙O2max = 22.9 ± 5.4 yr and 39.6 ± 5.6 mL·kg·min) performed HIIT and 32 men and women (age and V˙O2max = 25.7 ± 4.5 yr and 40.7 ± 5.2 mL·kg·min) were nonexercising controls (CON). The first 10 sessions of HIIT required eight to ten 60 s bouts of cycling at 90%-110% percent peak power output interspersed with 75 s recovery, followed by randomization to one of three regimes (sprint interval training (SIT), high-volume interval training (HIITHI), or periodized interval training (PER) for the subsequent 10 sessions. Before, midway, and at the end of training, progressive cycling to exhaustion was completed during which V˙O2max and maximal CO were estimated.

RESULTS

Compared with CON, significant (P < 0.001) increases in V˙O2max in HIIT + SIT (39.8 ± 7.3 mL·kg·min to 43.6 ± 6.1 mL·kg·min), HIIT + HIITHI (41.1 ± 4.9 mL·kg·min to 44.6 ± 7.0 mL·kg·min), and HIIT + PER (39.5 ± 5.6 mL·kg·min to 44.1 ± 5.4 mL·kg·min) occurred which were mediated by significant increases in maximal CO (20.0 ± 3.1 L·min to 21.7 ± 3.2 L·min, P = 0.04). Maximal stroke volume was increased with HIIT (P = 0.04), although there was no change in maximal HR (P = 0.88) or arteriovenous O2 difference (P = 0.36). These CO data are accurate and represent the mean changes from pre- to post-HIIT across all three training groups.

CONCLUSIONS

Increases in V˙O2max exhibited in response to different HIIT regimes are due to improvements in oxygen delivery.

High-intensity interval training and cardiac autonomic control in individuals with metabolic syndrome: A randomised trial

BACKGROUND

Insulin resistance has been postulated to play a central role in the co-appearance of various cardiovascular disease risk factors constituting the metabolic syndrome (MetS). There is evidence that altered cardiac autonomic function (CAF) may precede the onset of insulin resistance. Exercise training has been shown to improve CAF in different populations, yet little is known regarding the exercise dose response for CAF. The aim of this study was to investigate the impact of different volumes of high-intensity interval training (HIIT) and traditional moderate-intensity continuous training (MICT) on CAF in participants with MetS.

METHODS

Individuals with MetS (n=56) were randomised into the following 16-week training interventions: i) MICT (n=16, 30min at 60-70%HRpeak, 5×/week); ii) 4HIIT (n=19, 4×4min bouts at 85-95%HRpeak, interspersed with 3min of active recovery at 50-70%HRpeak, 3×/week); or iii) 1HIIT (n=21, 1×4min bout at 85-95%HRpeak, 3×/week). R-R interval recorded for 5min in a supine position at pre- and post-intervention was used to derive linear (SDNN, RMSSD, pNN50, LF, HF, LF/HF) and non-linear (SD1, SD2, Alpha1, Alpha2, SampEn) heart rate variability (HRV) indices as measures of CAF. Group×time interaction effects were examined (ANCOVA) and Eta squared (η²) interaction effect sizes calculated.

RESULTS

While there were no significant between-group differences in CAF indices, there were small-to-medium group×time interaction effects on SDNN [F(2,52)=0.70, p=0.50, η²=0.02], RMSSD [F(2,52)=1.35, p=0.27, η²=0.03], HF power [F(2,52)=1.27, p=0.29, η²=0.03], SD1 [F(2,52)=0.47, p=0.63, η²=0.01], and SD2 [F(2,52)=0.41, p=0.67, η²=0.01]. The following represent the relative percentage increases across these variables for 4HIIT, MICT, and 1HIIT respectively (SDNN, +30%, +17%, 9%; RMSSD, +30%, +22%, -2%; HF power, +69%, +18%, +7%; SD1, +30%, +22%,-2%; SD2, +22%, +14%, 4%).

CONCLUSIONS

There were no significant between-group differences for the effects of exercise dose on CAF indices, however; high-volume HIIT demonstrated the greatest magnitude of effect for improving CAF in individuals with MetS.

High Intensity Interval Training for Maximizing Health Outcomes

Regular physical activity and exercise training are important actions to improve cardiorespiratory fitness and maintain health throughout life. There is solid evidence that exercise is an effective preventative strategy against at least 25 medical conditions, including cardiovascular disease, stroke, hypertension, colon and breast cancer, and type 2 diabetes. Traditionally, endurance exercise training (ET) to improve health related outcomes has consisted of low- to moderate ET intensity. However, a growing body of evidence suggests that higher exercise intensities may be superior to moderate intensity for maximizing health outcomes. The primary objective of this review is to discuss how aerobic high-intensity interval training (HIIT) as compared to moderate continuous training may maximize outcomes, and to provide practical advices for successful clinical and home-based HIIT.

High-intensity interval training improves obstructive sleep apnoea

Background

Three hours per week of vigorous physical activity is found to be associated with reduced odds of sleep-disordered breathing.

Aim

To investigate whether 12 weeks of high-intensity interval training (HIIT) reduced the apnoea–hypopnea index (AHI) in obese subjects with moderate-to-severe obstructive sleep apnoea.

Methods

In a prospective randomised controlled exercise study, 30 (body mass index 37±6 kg/m², age 51±9 years) patients with sleep apnoea (AHI 41.5±25.3 events/hour) were randomised 1:1 to control or 12 weeks of supervised HIIT (4×4 min of treadmill running or walking at 90%–95% of maximal heart rate two times per week).

Results

In the HIIT group, the AHI was reduced by 7.5±11.6 events/hour (within-group p<0.05), self-reported sleepiness (Epworth scale) improved from 10.0±3.6 to 7.3±3.7 (between-group p<0.05) and maximal oxygen uptake improved from 28.2±7.4 to 30.2±7.7 mL/kg/min (between-group p<0.05) from baseline to 12 weeks. The AHI, self-reported sleepiness and VO_2maxwere unchanged from baseline to 12 weeks in controls (baseline AHI 50.3±25.5 events/hour, Epworth score 5.9±4.3, maximal oxygen uptake 27.0±6.8 mL/kg/min). Body weight remained unchanged in both groups.

Conclusion

Twelve weeks of HIIT improved the AHI and self-reported daytime sleepiness in subjects with obese sleep apnoea without any change in the desaturation index and body weight.

Investigating human skeletal muscle physiology with unilateral exercise models: when one limb is more powerful than two

Direct sampling of human skeletal muscle using the needle biopsy technique can facilitate insight into the biochemical and histological responses resulting from changes in exercise or feeding. However, the muscle biopsy procedure is invasive, and analyses are often expensive, which places pragmatic restraints on sample sizes. The unilateral exercise model can serve to increase statistical power and reduce the time and cost of a study. With this approach, 2 limbs of a participant are randomized to 1 of 2 treatments that can be applied almost concurrently or sequentially depending on the nature of the intervention. Similar to a typical repeated measures design, comparisons are made within participants, which increases statistical power by reducing the amount of between-person variability. A washout period is often unnecessary, reducing the time needed to complete the experiment and the influence of potential confounding variables such as habitual diet, activity, and sleep. Variations of the unilateral exercise model have been employed to investigate the influence of exercise, diet, and the interaction between the 2, on a wide range of variables including mitochondrial content, capillary density, and skeletal muscle hypertrophy. Like any model, unilateral exercise has some limitations: it cannot be used to study variables that potentially transfer across limbs, and it is generally limited to exercises that can be performed in pairs of treatments. Where appropriate, however, the unilateral exercise model can yield robust, well-controlled investigations of skeletal muscle responses to a wide range of interventions and conditions including exercise, dietary manipulation, and disuse or immobilization.

High-intensity interval training: a review of its impact on glucose control and cardiometabolic health

Exercise plays a central role in the management and treatment of common metabolic diseases, but modern society presents many barriers to exercise. Over the past decade there has been considerable interest surrounding high-intensity interval training (HIIT), with advocates claiming it can induce health benefits of similar, if not superior magnitude to moderate-intensity continuous exercise, despite reduced time commitment. As the safety of HIIT becomes clearer, focus has shifted away from using HIIT in healthy individuals towards using this form of training in clinical populations. The continued growth of metabolic disease and reduced physical activity presents a global health challenge and effective therapies are urgently required. The aim of this review is to explore whether the acclaim surrounding HIIT is justified by examining the effect of HIIT on glucose control, its ability to affect cardiovascular function and the underlying mechanisms of the changes observed in those with common metabolic diseases. It also explores translation of the research into clinical practice.

Physiological adaptations to interval training and the role of exercise intensity

Interval exercise typically involves repeated bouts of relatively intense exercise interspersed by short periods of recovery. A common classification scheme subdivides this method into high-intensity interval training (HIIT; 'near maximal' efforts) and sprint interval training (SIT; 'supramaximal' efforts). Both forms of interval training induce the classic physiological adaptations characteristic of moderate-intensity continuous training (MICT) such as increased aerobic capacity (V̇O2 max ) and mitochondrial content. This brief review considers the role of exercise intensity in mediating physiological adaptations to training, with a focus on the capacity for aerobic energy metabolism. With respect to skeletal muscle adaptations, cellular stress and the resultant metabolic signals for mitochondrial biogenesis depend largely on exercise intensity, with limited work suggesting that increases in mitochondrial content are superior after HIIT compared to MICT, at least when matched-work comparisons are made within the same individual. It is well established that SIT increases mitochondrial content to a similar extent to MICT despite a reduced exercise volume. At the whole-body level, V̇O2 max is generally increased more by HIIT than MICT for a given training volume, whereas SIT and MICT similarly improve V̇O2 max despite differences in training volume. There is less evidence available regarding the role of exercise intensity in mediating changes in skeletal muscle capillary density, maximum stroke volume and cardiac output, and blood volume. Furthermore, the interactions between intensity and duration and frequency have not been thoroughly explored. While interval training is clearly a potent stimulus for physiological remodelling in humans, the integrative response to this type of exercise warrants further attention, especially in comparison to traditional endurance training.

Salutary effects of high-intensity interval training in persons with elevated cardiovascular risk

Although moderate-intensity continuous training (MICT) has been the traditional model for aerobic exercise training for over four decades, a growing body of literature has demonstrated equal if not greater improvement in aerobic capacity and similar beneficial effects on body composition, glucose metabolism, blood pressure, and quality of life from high-intensity interval training (HIIT). An advantage of HIIT over MICT is the shorter time required to perform the same amount of energy expenditure. The current brief review summarizes the effects of HIIT on peak aerobic capacity and cardiovascular risk factors in healthy adults and those with various cardiovascular diseases, including coronary artery disease, chronic heart failure, and post heart transplantation.

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.