High-intensity interval training, solutions to the programming puzzle. Part II: anaerobic energy, neuromuscular load and practical applications

Development potentials of commonly used high-intensity training strategies on central and peripheral components of maximal oxygen consumption

The aim of this study was to reveal the development potentials of five high-intensity training models on central and peripheral components of maximal oxygen consumption (VO_2max). Following VO_2max determination, maximal cardiac output (Q_max), maximal stroke volume (SV_max), and maximal arteriovenous O₂ difference (a-vO_{2diff_max}) were analysed. Short-interval- (short-HIIT), long-interval (long-HIIT), alternating work-rate continuous (alter-HIT), constant work-rate continuous (const-HIT), and sprint interval (SIT) sessions were performed on separate days with iso-effort and iso-time methods. Time spent (t_spent) at > 95% of VO_2max was the highest in long-HIIT (p < 0.05). The t_spent at > 90% of Q_max was higher in alter-HIT than long-HIIT and SIT (p < 0.05), while there was no significant difference for t_spent at > 90% of SV_max amongst high-intensity trainings. The t_spent at > 90% of a-vO_2diff__max was higher in short-HIIT and long-HIIT than other modalities (p < 0.05). It can be said that continuous modalities seem to have a higher potential to improve central part of VO_2max, while interval modalities may be better to develop peripheral component.

Science and Hurling: A Review

Hurling is one of the world’s fastest field sports. Since the last review of science and Gaelic sports in 2008, there has been an increase in sports science provisions across elite and sub-elite cohorts, resulting in increased hurling-specific literature equating to an additional 111 research investigations into the game across all sports science disciplines. The present review aims to provide an updated analysis of the current research on the game and propose recommendations for future research. Overall, intermittent aerobic fitness remains an important physical quality during competition, with a focus on games-based training methodologies within the literature. Within the current review, we provide updated normative data on the running demands, physiological responses, and anthropometric and performance profiles of hurling players. The increased literature across the sport has led to the development of a hurling-specific simulation, that can now be utilised practically in training and research processes for hurling cohorts. Furthermore, the monitoring of internal and external training loads across training and match environments, in addition to response variables such as well-being, appears to have become more prominent, allowing practitioners to design training regimes to achieve optimal dose and response characteristics. Analysing the game from a scientific perspective can allow for more efficient preparatory practices, to meet the specific requirements of players at all age levels. Collaborative research among the various sports science disciplines, is required to identify strategies to reduce the incidence of injury and enhance performance in hurling. The current review provides updated information to coaches and practitioners regarding position-specific physical qualities, and match-play demands that can concurrently support the training process within hurling.

Physiological and locomotor demands during small-sided games are related to match demands and physical fitness? A study conducted on youth soccer players

AIM

The purpose of the study was: (i) to analyze the relationships of physiological and locomotor demands between small-sided games (3v3 and 5v5) and official matches (11v11); (ii) to analyze the relationships between small-sided games demands and the physical fitness of youth soccer players.

METHODS

The observational study lasted three weeks. In the first week participants performed the 5v5 (50 × 31 and 40 × 25 m) repeatedly over four days. In the third week they repeatedly performed the 3v3 (39 × 24 and 32 × 19 m) over four consecutive days. Twenty youth soccer players (age: 16.8 ± 0.41) were tested twice for their final velocity at 30-15 Intermittent Fitness test (VIFT), peak speed attained at 30-m sprint test (peak speed), and anaerobic speed reserve (ASR). The heart rate responses and locomotor demands were monitored in the SSGs (3v3 and 5v5) and matches (11v11) occurring once a week. The Polar Team Pro was used as the instrument to monitor heart rate and locomotor demands. Three official matches were also monitored during the period.

RESULTS

Results revealed no significant correlations (p > 0.05) between small-sided games and match physiological or locomotor demands. However, VIFT and ASR were significantly correlated with distance covered at 5v5 (r = 0.483; p = 0.031; and r = - 0.474; p = 0.035, respectively), average speed (r = 0.474; p = 0.035; and r = - 0.453; p = 0.045, respectively), while VIFT was also significantly correlated with distance covered at Z2 intensity (r = 0.510; p = 0.022).

CONCLUSIONS

The results suggest that the physiological and locomotor demands occurring in small-sided games are significantly different from those occurring in official matches. Thus, physiological and locomotor similarities between small-sided games and official matches are scarce. Considering the second purpose of this study, the results suggest that VIFT and ASR are important physical fitness parameters to modulate the amount of distance covered by the players in 5v5, the average pace, and also the distance covered at high intensities.

Physiological, perceptual and affective responses to high-intensity interval training using two work-matched programs with different bout duration in obese males

Objectives

This study compared physiological, perceptual, and affective responses to high-intensity interval training (HIIT) between two work-matched programs with different bout durations in obese males.

Methods

Sixteen low-to-moderately active obese men completed an eight-week cycling program of supervised HIIT (3 days/week) using either short bouts [48 × 10 s at 100% of peak power output (PPO) with 15 s of recovery (HIIT10)] or long bouts [8 × 60 s at 100% PPO with 90 s of recovery (HIIT60)]. Workload was progressively adjusted, to maintain high intensity (100% PPO), throughout training. Blood lactate (BLa), heart rate (HR), ratings of perceived exertion (RPE), and feeling scale ratings (pleasure/displeasure) were measured in each HIIT session.

Results

Average HR decreased in the last 2 weeks of training in both groups by 2.2 ± 1.8% of peak HR (p < 0.001). Training resulted in a reduction in BLa during exercise by 28 ± 19% (p < 0.001) from the 10th min onward only in HIIT10. Similarly, during the last weeks of training, RPE decreased (by 1.0 ± 1.1 units, p < 0.05) and feeling scale ratings were improved only in HIIT10, while RPE remained unchanged and feeling scale ratings deteriorated in HIIT60 (from 3.0 ± 1.1 to 2.1 ± 0.9 units, p < 0.001). No differences in post-exercise enjoyment were found.

Conclusion

Both HIIT formats induced similar HR adaptations, but improvement of BLa, perceptual and affective responses occurred only when bout duration was shorter. Our findings suggest that, in low-to-moderately active obese men, HIIT may be more effective in improving metabolic, perceptual, and affective responses when shorter, rather than longer, bouts of exercise are used.

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.

High-intensity interval training elicits more enjoyment and positive affective valence than moderate-intensity training over a 12-week intervention in overweight young women

Background

The purpose of this study was to compare the differences in enjoyment and affect in response to four weight control intervention protocols over 12 weeks.

Methods

Sixty overweight young females were randomised into four intervention groups: repeated sprint training (RST, 6-sec all-out sprint interspersed with 9-sec rest), high-intensity interval training (HIIT) with short interval (HIIT₁₂₀, 1-min effort at 120% V̇O_2peak) and long interval (HIIT₉₀, 4-min effort at 90% V̇O_2peak), and moderate-intensity continuous training (MICT, 60% V̇O_2peak) by cycling over 12 weeks. The total workload in each training session in HIIT₁₂₀, HIIT₉₀, and MICT was confined to 200 kJ, while it was lower in RST with 57 ± 4 kJ. Enjoyment (Physical Activity Enjoyment Scale, PACES) and affective valence (Feeling Scale, FS) were measured throughout the intervention.

Results

The score of the PACES on average over 12 weeks showed a significant between-group effect that was lower in MICT (80.8 ± 11.8) compared with HIIT₁₂₀ (92.5 ± 11.4) and HIIT₉₀ (96.8 ± 13.9) (p < 0.05). In the 8th week, enjoyment was scored higher in two HIITs compared with MICT. In the 12th week, HIITs and RST were more enjoyable than MICT, where two HIITs were better than RST. The score of FS showed a significant between-group effect that was higher in HIIT₉₀ (1.5 ± 1.4) compared with HIIT₁₂₀ (0.2 ± 1.2) (p < 0.05), but a non-significant time or group-by-time interaction effect. A significant weight loss occurred in three interval training protocols (p < 0.05), but not in MICT. The V̇O_2peak significantly increased in four groups without between-group difference.

Conclusion

Interval training, especially the long-interval type, is an enjoyable and pleasant long-term exercise intervention for overweight young women. RST could be an alternative for weight control considering its time efficiency with comparable enjoyment and overall pleasure.

Effects of small-sided games and running-based high-intensity interval training on body composition and physical fitness in under-19 female soccer players

Background

The aim of this study was to compare the effects of small-sided games (SSGs) and running-based high-intensity interval training (HIIT) on the body composition and physical fitness of youth female soccer players.

Methods

This study followed a randomized parallel study design. Twenty-four female soccer players (age: 18.63 ± 2.36 years) were randomly allocated to two training groups (SSG, n = 12; and HIIT, n = 12). The training intervention had a duration of eight weeks, consisting of three training sessions per week. Players were assessed twice (pre- and post-intervention) for anthropometrics, vertical (countermovement jumps, CMJ; and drop jumps, DJ) and horizontal jumping (single, triple and crossover hop), sprinting (10- and 30-m), change-of-direction (COD), COD deficit and final velocity at 30–15 Intermittent Fitness Test (V_IFT). A covariance analysis (ANCOVA) was used to determine differences between the groups in the effect on post-intervention by controlling for covariates (pre-intervention). The within-group analysis (time) was performed using a paired t-test, while the between-group analysis per assessment moment was performed using an independent t-test.

Results

The between-group analysis with ANCOVA revealed that there are no significant differences between the SSG and HIIT groups in the post-intervention for any outcome (p > 0.05). The within-group analysis revealed significant improvements in both the SSG and HIIT groups in CMJ (p < 0.05), single, triple and crossover hops (p < 0.05), RSI DJ 30-cm and RSI DJ 40-cm (p < 0.05), VIFT (p < 0.05) and COD (p < 0.05).

Conclusions

SSG and HIIT are both effective for improving vertical and horizontal jumping ability, change-of-direction, and aerobic capacity status measured at a progressive and intermittent multistage test in youth soccer players.

The Salzburg 10/7 HIIT shock cycle study: the effects of a 7-day high-intensity interval training shock microcycle with or without additional low-intensity training on endurance performance, well-being, stress and recovery in endurance trained athletes-study protocol of a randomized controlled trial

BACKGROUND

Performing multiple high-intensity interval training (HIIT) sessions in a compressed period of time (approximately 7-14 days) is called a HIIT shock microcycle (SM) and promises a rapid increase in endurance performance. However, the efficacy of HIIT-SM, as well as knowledge about optimal training volumes during a SM in the endurance-trained population have not been adequately investigated. This study aims to examine the effects of two different types of HIIT-SM (with or without additional low-intensity training (LIT)) compared to a control group (CG) on key endurance performance variables. Moreover, participants are closely monitored for stress, fatigue, recovery, and sleep before, during and after the intervention using innovative biomarkers, questionnaires, and wearable devices.

METHODS

This is a study protocol of a randomized controlled trial that includes the results of a pilot participant. Thirty-six endurance trained athletes will be recruited and randomly assigned to either a HIIT-SM (HSM) group, HIIT-SM with additional LIT (HSM + LIT) group or a CG. All participants will be monitored before (9 days), during (7 days), and after (14 days) a 7-day intervention, for a total of 30 days. Participants in both intervention groups will complete 10 HIIT sessions over 7 consecutive days, with an additional 30 min of LIT in the HSM + LIT group. HIIT sessions consist of aerobic HIIT, i.e., 5 × 4 min at 90-95% of maximal heart rate interspersed by recovery periods of 2.5 min. To determine the effects of the intervention, physiological exercise testing, and a 5 km time trial will be conducted before and after the intervention.

RESULTS

The feasibility study indicates good adherence and performance improvement of the pilot participant. Load monitoring tools, i.e., biomarkers and questionnaires showed increased values during the intervention period, indicating sensitive variables.

CONCLUSION

This study will be the first to examine the effects of different total training volumes of HIIT-SM, especially the combination of LIT and HIIT in the HSM + LIT group. In addition, different assessments to monitor the athletes' load during such an exhaustive training period will allow the identification of load monitoring tools such as innovative biomarkers, questionnaires, and wearable technology.

TRIAL REGISTRATION

clinicaltrials.gov, NCT05067426. Registered 05 October 2021-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT05067426 . Protocol Version Issue date: 1 Dec 2021. Original protocol. Authors: TLS, NH.

School-based high-intensity interval training programs in children and adolescents: A systematic review and meta-analysis

PURPOSE

1) To investigate the effectiveness of school-based high-intensity interval training (HIIT) interventions in promoting health outcomes of children and adolescents compared with either a control group or other exercise modality; and 2) to explore the intervention characteristics and process outcomes of published school-based HIIT interventions.

METHODS

We searched Medline, Embase, CINAHL, SPORTDiscus, and Web of Science from inception until 31 March 2021. Studies were eligible if 1) participants aged 5-17 years old; 2) a HIIT intervention within a school setting ≥ 2 weeks duration; 3) a control or comparative exercise group; 4) health-related, cognitive, physical activity, nutrition, or program evaluation outcomes; and 5) original research published in English. We conducted meta-analyses between HIIT and control groups for all outcomes with ≥ 4 studies and meta-regressions for all outcomes with ≥ 10 studies. We narratively synthesised results between HIIT and comparative exercise groups.

RESULTS

Fifty-four papers met eligibility criteria, encompassing 42 unique studies (35 randomised controlled trials; 36 with a high risk of bias). Meta-analyses indicated significant improvements in waist circumference (mean difference (MD) = -2.5cm), body fat percentage (MD = -1.7%), body mass index (standardised mean difference (SMD) = -1.0), cardiorespiratory fitness (SMD = +1.0), resting heart rate (MD = -5bpm), homeostatic model assessment-insulin resistance (MD = -0.7), and low-density lipoprotein cholesterol (SMD = -0.9) for HIIT compared to the control group. Our narrative synthesis indicated mixed findings between HIIT and other comparative exercise groups.

CONCLUSION

School-based HIIT is effective for improving several health outcomes. Future research should address the paucity of information on physical activity and nutrition outcomes and focus on the integration and long-term effectiveness of HIIT interventions within school settings.

TRIAL REGISTRATION NUMBER

PROSPERO CRD42018117567.

High-intensity interval resistance training (HIIRT) improves liver gluconeogenesis from lactate in Swiss mice

High-intensity physical exercise favors anaerobic glycolysis and increases lactatemia. Lactate is converted back to glucose in the liver, so that the lactate threshold, an indicator of physical performance, must be related to the gluconeogenic capacity of the liver. This research assessed the effect of a high-intensity interval resistance training (HIIRT) on liver gluconeogenesis from lactate. Swiss mice were trained (groups T) on vertical ladder with overload of 90% of their maximal load. Control animals remained untrained (groups C0 and C8). In situ liver perfusion with lactate and adrenaline was performed in rested mice after 6 hours of food deprivation. There were larger outputs of glucose (T6, 71.90%; T8, 54.53%) and pyruvate (T8, 129.28%) (representative values for 4 mM lactate) in the groups trained for 6 or 8 weeks (T6 and T8), and of glucose in the presence of adrenaline in group T8 (280%). The content of PEPCK, an important regulatory enzyme of the gluconeogenic pathway, was 69.13% higher in group T8 than in the age-matched untrained animals (C8). HIIRT augmented liver gluconeogenesis from lactate and this might improve the lactate threshold. Novelty: The liver metabolizes lactate from muscle into glucose. Physical training may enhance the gluconeogenic capacity of the liver. As lactate clearance by the liver improves, lactate threshold is displaced to higher exercise intensities.

How Do the Effects of an 8-Week Intervention Influence Subsequent Performance Development in Cross-Country Skiers?

PURPOSE

To investigate how the effects of increased low- versus high-intensity endurance training in an 8-week intervention influenced the subsequent development of performance and physiological indices in cross-country skiers.

METHODS

Forty-four (32 men and 12 women) junior cross-country skiers were randomly assigned into a low-intensity training group (LITG, n = 20) or high-intensity training group (HITG, n = 24) for an 8-week intervention followed by 5 weeks of standardized training with similar intensity distribution, and thereafter 14 weeks of self-chosen training. Performance and physiological indices in running and in roller-ski skating were determined preintervention, after the intervention, and after the standardized training period. Roller-ski skating was also tested after the period of self-chosen training.

RESULTS

No between-groups changes from preintervention to after the standardized training period were found in peak speed when incremental running and roller-ski skating (P = .83 and .51), although performance in both modes was improved in the LITG (2.4% [4.6%] and 3.3% [3.3%], P < .05) and in roller-ski skating for HITG (2.6% [3.1%], P < .01). While improvements in maximal oxygen consumption running and peak oxygen uptake roller-ski skating were greater in HITG than in LITG from preintervention to after the intervention, no between-groups differences were found from preintervention to after the standardized training period (P = .50 and .46), although peak oxygen uptake in roller-ski skating significantly improved in HITG (5.7% [7.0%], P < .01). No changes either within or between groups were found after the period of self-chosen training.

CONCLUSIONS

Differences in adaptations elicited by a short-term intervention focusing on low- versus high-intensity endurance training had little or no effect on the subsequent development of performance or physiological indices following a period of standardized training in cross-country skiers.

Effects of short sprint interval training on aerobic and anaerobic indices: A systematic review and meta-analysis

The effects of short sprint interval training (sSIT) with efforts of ≤10 seconds on maximal oxygen consumption (V̇O₂ max), aerobic and anaerobic performances remain unknown. To verify the effectiveness of sSIT in physically active adults and athletes, a systematic literature search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The databases PubMed/MEDLINE, ISI Web of Science, SPORTDiscus were systematically searched on the 9^th of May 2020 and updated on the 14^th of September 2021. Inclusion criteria were based on PICO and included healthy athletes and active adults of any sex (≤40 years), performing supervised sSIT (≤10 s of "all out" and non "all out" efforts) of at least 2 weeks, with a minimum of 6 sessions. As a comparator, a non-sSIT control group, another high-intensity interval training (HIIT) group, or a continuous training (CT) group were required. A total of 18 studies was deemed eligible. The estimated SMDs based on the random-effects model were -0.56 (95% CI: -0.79, -0.33, p < 0.001) for V̇O₂ max, -0.43 (95% CI: -0.67, -0.20, p < 0.001) for aerobic performance, and -0.44 (95% CI: -0.70, -0.18, p < 0.001) for anaerobic performance after sSIT vs. no exercise/usual training. However, there were no significant differences (p > 0.05) for all outcomes when comparing sSIT vs. HIIT/CT. Our findings indicate a very high effectiveness of sSIT protocols in different exercise modes (e.g. cycling, running, paddling, punching) to improve V̇O₂ max, aerobic and anaerobic performances in physically active young healthy adults and athletes.

Measurement properties of external training load variables during standardised games in soccer: Implications for training and monitoring strategies

The aim of this study was to assess the measurement properties of external training load measures across three formats of standardised training games. Eighty-eight players from two English professional soccer clubs participated in the study spanning three consecutive seasons. External training load data was collected from three types of standardised game format drills (11v11, 10v10, 7v7+6) using Global Positioning Systems. For each external training load metric in each game format, the following measurement properties were calculated; coefficient of variation (CV%) to determine between- and within-subject reliability, intraclass coefficient correlation (ICC) to determine test-retest reliability, and signal-to-noise ratio (SNR) to determine sensitivity. Total distance (TD) and PlayerLoad^™ (PL) demonstrated good sensitivity (TD SNR = 1.6–4.6; PL SNR = 1.2–4.3) on a group level. However, a wide variety of within-subject reliability was demonstrated for these variables (TD CV% = 1.7–36.3%; PL CV% = 4.3–39.5%) and corresponding intensity measures calculated per minute. The percentage contribution of individual planes to PL showed the lowest between-subject CV% (CV% = 2–7%), although sensitivity varied across formats (SNR = 0.3–1.4). High speed running demonstrated poor reliability across all three formats of SSG (CV% = 51–103%, ICC = 0.03–0.53). Given the measurement properties of external training load measures observed in this study, specifically the within-subject variation, reliability across trials of standardised training games should be calculated on an individual level. This will allow practitioners to detect worthwhile changes across trials of standardised game format drills. Such information is important for the appropriate implementation of training and monitoring strategies in soccer.

Effect of Interval Training on the Factors Influencing Maximal Oxygen Consumption: A Systematic Review and Meta-Analysis

BACKGROUND

The maximal rate of oxygen consumption (VO_2max) is an important measure in exercise science as it is an indicator of cardiorespiratory fitness. Individual studies have identified central and peripheral adaptions to interval training that may underlie improvements in VO_2max, but there is no compilation of results.

OBJECTIVE

We aimed to systematically review the adaptive responses to high-intensity interval training (HIIT) and sprint interval training (SIT) on the central and peripheral factors influencing VO_2max in healthy individuals.

DATA SOURCES

SPORTDiscus and MEDLINE (up to and including 13 June, 2020) were explored to conduct the literature search.

STUDY SELECTION

Reviewed studies met the following criteria: (1) were in the English language; (2) prospective in nature; (3) included at least three interval sessions or were at least 1 week in duration; (4) contained HIIT or SIT; (5) involved participants between the ages of 18 and 65 years; and (6) included at least one of the following central (blood volume, plasma volume, hemoglobin mass, left ventricular mass, maximal stroke volume, maximal cardiac output) or peripheral factors (capillary density, maximal citrate synthase activity, mitochondrial respiration associated with VO_2max).

RESULTS

Thirty-two studies (369 participants, 49 were female) were included in the quantitative analyses, consisting of both HIIT (n = 18) and SIT (n = 17) interventions. There were only statistically significant changes in hematological measures (plasma volume) following HIIT. There was a significant increase in left ventricular mass following HIIT (7.4%, p < 0.001) and SIT (5.3%, p = 0.007) in inactive individuals, though the change following SIT may be misleading. There was only a significant increase in maximal stroke volume (14.1%, p = 0.015) and maximal cardiac output (12.6%, p = 0.002) following HIIT. In addition to central factors, there was a significant increase in capillary density (13.8%, p < 0.001) following SIT in active individuals. With respect to maximal citrate synthase activity, there were improvements following HIIT (20.8%, p < 0.001) and SIT (15.7%, p < 0.001, I² = 97%) in active individuals. The results for mitochondrial respiration suggested that there was no statistically significant improvement following HIIT (5.0%, p = 0.585).

CONCLUSIONS

Improvements in the central and peripheral factors influencing VO_2max were dependent on the interval type. Only HIIT led to a statistically significant improvement in cardiac function. Both HIIT and SIT increased maximal citrate synthase activity, while changes in other peripheral measures (capillary density, mitochondrial respiration) only occurred with SIT.

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

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

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

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

Mechanical, Cardiorespiratory, and Muscular Oxygenation Responses to Sprint Interval Exercises Under Different Hypoxic Conditions in Healthy Moderately Trained Men

Objective: The aim of this study was to determine the effects of sprint interval exercises (SIT) conducted under different conditions (hypoxia and blood flow restriction [BFR]) on mechanical, cardiorespiratory, and muscular O₂ extraction responses.

Methods: For this purpose, 13 healthy moderately trained men completed five bouts of 30 s all-out exercises interspaced by 4 min resting periods with lower limb bilateral BFR at 60% of the femoral artery occlusive pressure (BFR₆₀) during the first 2 min of recovery, with gravity-induced BFR (pedaling in supine position; G-BFR), in a hypoxic chamber (FiO₂≈13%; HYP) or without additional stress (NOR). Peak and average power, time to achieve peak power, rating of perceived exertion (RPE), and a fatigue index (FI) were analyzed. Gas exchanges and muscular oxygenation were measured by metabolic cart and NIRS, respectively. Heart rate (HR) and peripheral oxygen saturation (SpO₂) were continuously recorded.

Results: Regarding mechanical responses, peak and average power decreased after each sprint (p < 0.001) excepting between sprints four and five. Time to reach peak power increased between the three first sprints and sprint number five (p < 0.001). RPE increased throughout the exercises (p < 0.001). Of note, peak and average power, time to achieve peak power and RPE were lower in G-BFR (p < 0.001). Results also showed that SpO₂ decreased in the last sprints for all the conditions and was lower for HYP (p < 0.001). In addition, Δ[O₂Hb] increased in the last two sprints (p < 0.001). Concerning cardiorespiratory parameters, BFR₆₀ application induced a decrease in gas exchange rates, which increased after its release compared to the other conditions (p < 0.001). Moreover, muscle blood concentration was higher for BFR₆₀ (p < 0.001). Importantly, average and peak oxygen consumption and muscular oxyhemoglobin availability during sprints decreased for HYP (p < 0.001). Finally, the tissue saturation index was lower in G-BFR.

Conclusions: Thus, SIT associated with G-BFR displayed lower mechanical, cardiorespiratory responses, and skeletal muscle oxygenation than the other conditions. Exercise with BFR₆₀ promotes higher blood accumulation within working muscles, suggesting that BFR₆₀ may additionally affect cellular stress. In addition, HYP and G-BFR induced local hypoxia with higher levels for G-BFR when considering both exercise bouts and recovery periods.

Combining small-sided soccer games and running-based methods: A systematic review

Small-sided games (SSGs) are often used in soccer to produce acute physiological and physical responses, while a tactical/technical stimulus is also employed. However, due to some limitations of SSGs, researchers have been testing this method combined with running-based training methods. This systematic review was conducted to assess the effects of combined SSG and running-based methods on soccer players' acute responses and adaptations after training interventions. A systematic review of Web of Science, PubMed, Cochrane Library, Scopus, and SPORTDiscus databases was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The database search initially identified 782 titles. From those, five articles were deemed eligible for the systematic review. The five included studies presented data from training load, reporting inconsistent greater values in combined SSG and running-based methods when compared to SSG-only formats. Considering the adaptations, studies comparing combined SSG and running-based methods with SSG-only methods revealed inconsistent differences in terms of the effects on aerobic performance and sprinting. Combining SSG and running-based methods can increase the acute mechanical load and high-intense running stimuli in players when compared to interventions that use only SSGs. However, the adaptations promoted by both methods are similar, and the differences are unclear. The order of combination (SSG and running-based method) does not seem to impact players' adaptations; however, the frequency of sessions did have a meaningful impact.

Short-term effects of on-field combined core strength and small-sided games training on physical performance in young soccer players

This study aimed to compare the effects of 6-weeks combined core strength and small-sided games training (SSG_core) vs. small-sided games (SSG) training on the physical performance of young soccer players. Thirty-eight amateur soccer players (age: 16.50 ± 0.51 years) were randomly assigned to either a SSG_core (n = 20) or a SSG group (n = 18). The SSG_core group performed upper and lower body core strength exercises combined with SSG including 2-, 3- and 4-a-sided soccer games third a week. The SSG group performed only the SSG periodization. Baseline and after the 6-week training period the Yo-Yo Intermittent Recovery Test level 1 (YYIRTL-1), 5–20-m sprint test, countermovement jump (CMJ), squat jump (SJ), triple-hop distance (THD), zigzag agility with ball (ZAWB) and without ball (ZAWOB), three corner run test (TCRT) and Y-balance test. The SSG_core group demonstrated meaningful improvements in 20 m sprint time (SSG_core: -9.1%, d = 1.42; SSG: -4.4%, d = 0.76), CMJ (SSG_core: 11.4%, d = 2.67; SSG: -7.7%, d = 1.43), SJ (SSG_core: 12.0%, d = 2.14; SSG: 5.7%, d = 1.28), THD (SSG_core: 5.0%, d = 1.39; SSG: 2.7%, d = 0.52) and TCRT (SSG_core: -3.7%, d = 0.69; SSG: -1.9%, d = 0.38). Furthermore, the SSG_core group demonstrated meaningfully higher improvement responses in both leg balance score (d = ranging from 2.11 to 2.75) compared with SSG group. These results suggest that the inclusion of core strength training to a SSG periodization is greatly effective to improve speed and strength-based conditioning in young soccer players.

Home-Based HIIT and Traditional MICT Prescriptions Improve Cardiorespiratory Fitness to a Similar Extent Within an Exercise Referral Scheme for At-Risk Individuals

Exercise referral schemes (ERS) are used to promote physical activity within primary care. Traditionally, ERS are conducted in a gym or leisure-center setting, with exercise prescriptions based on moderate-intensity continuous training (MICT). Home-based high-intensity interval training (Home-HIIT) has the potential to reduce perceived barriers to exercise, including lack of time and access to facilities, compared to traditional MICT prescription used with ERS and improve health related outcomes. We hypothesized that Home-HIIT would mediate greater improvement in cardiorespiratory fitness (CRF) by virtue of greater adherence and compliance to the exercise prescription, compared to MICT. Methods: Patients enrolled on an ERS (Liverpool, United Kingdom) were recruited for a pragmatic trial. Participants self-selected either 12 weeks of MICT (45-135 min/week at 50-70% HR_max) or Home-HIIT (4-9 min × 1 min intervals at ≥80% of HR_max, interspersed with 1 min rest). The primary outcome was the change in CRF (VO_{2 peak}) at post-intervention (12 weeks) and follow-up (3-month post intervention), using intention-to-treat analysis. Results: 154 participants (age 48 ± 10y; BMI 30.5 ± 6.1 kg/m²) were recruited between October 2017 and March 2019, 87 (56%) participants chose Home-HIIT and 67 (44%) MICT. VO_{2 peak} increased post-intervention in both groups (MICT 3.9 ± 6.0 ml.kg^-1.min^-1, Home-HIIT 2.8 ± 4.5 ml.kg^-1.min^-1, P < 0.001), and was maintained at follow-up (P < 0.001). Fat mass was only reduced post MICT (MICT -1.5 ± 6.3 kg, P < 0.05, Home-HIIT -0.2 ± 2.0 kg, P = 1.00), but the reduction was not maintained at follow-up (MICT -0.6 ± 5.1 kg, Home-HIIT 0.0 ± 2.2 kg, P > 0.05). Adherence to the prescribed programs was similar (MICT 48 ± 35%, Home-HIIT 39 ± 36%, P = 0.77). Conclusion: This is the first study to evaluate the use of Home-HIIT for individuals in a primary care setting. Contrary to our hypothesis, adherence to both exercise prescriptions was poor, and CRF improved to a similar extent in both groups with improvements maintained at 3-month follow-up. We provide evidence that, although not superior, Home-HIIT could be an effective and popular additional exercise choice for patients within primary care based ERS. Clinical Trial Registration: [ClinicalTrials.gov], identifier [NCT04553614].

Training Intensity, Not Duration, May Be Key to Upregulating Presynaptic Proteins of Calcium Dynamics and Calcium-Dependent Exocytosis in Fast- and Slow-Twitch Skeletal Muscles, in Addition to Maintaining Performance After Detraining

Neuromuscular adaptations are essential for improving athletic performance. However, little is known about the effect of different endurance training protocols and their subsequent detraining on the gene expression of critical factors for neuromuscular synaptic transmission. Therefore, this study investigated the effects of endurance training (high-intensity interval training [HIIT], continuous [cEND], mixed interval [Mix], and all protocols combined [Comb]) and detraining on performance and gene expression (GE) of the alpha-1a, synaptotagmin II (Syt-II), synaptobrevin II (Vamp2), and acetylcholinesterase (AChE) in the gastrocnemius and soleus of Wistar rats. Eighty rodents were randomly divided into control, HIIT, cEND, Mix, Comb, and detraining groups. The rodents trained for 6 weeks (5 × /week), followed by 2 weeks of detraining. Performance improved in all training groups and decreased following detraining (p < 0.05), except HIIT. In the gastrocnemius, alpha-1a GE was upregulated in the Mix. Syt-II and AChE GE were upregulated in HIIT, Mix, and Comb. Vamp2 GE was upregulated in all groups. In the soleus, alpha-1a GE was upregulated in HIIT, Mix, and Comb. Syt-II and Vamp2 GE were upregulated in all groups. AChE GE was upregulated in cEND, Mix, and Comb. Detraining downregulated mostly the gene expression in the skeletal muscles. We conclude that training intensity appears to be a key factor for the upregulation of molecules involved in neuromuscular synaptic transmission. Such changes occur to be involved in improving running performance. On the other hand, detraining negatively affects synaptic transmission and performance.

Effect of High-Intensity Interval Training on Quality of Life, Sleep Quality, Exercise Motivation and Enjoyment in Sedentary People with Type 1 Diabetes Mellitus

(1) Background: Type 1 diabetes mellitus (T1DM) people’s health-related quality of life (HRQoL) is affected by glycemic control. Regular exercise is strongly recommended to these patients due to its cardiovascular and metabolic benefits. However, a large percentage of patients with T1DM people present a sedentary behavior because of the fear of a post-exercise hypoglycemia event, lack of time, lack of motivation and the complicated management of exercise, glycemic and insulin dose interaction. High-intensity interval training (HIIT) is an efficient and safe methodology since it prevents hypoglycemia and does not require much time, which are the main barriers for this population to doing exercise and increasing physical conditioning. (2) Methods: Nineteen sedentary adults (37 ± 6.5 years) with T1DM, were randomly assigned to 6 weeks of either HIIT (12-16-20 × 30-s intervals interspersed with 1-min rest periods) performed thrice weekly, or to the control group, which did not train. HRQoL, sleep quality, exercise motivation and enjoyment were measured as psychological variables. (4) Results: HRQoL improved in physical and social domains, PF (1.9%); PR (80.3%); GH (16.6); SF (34.1%). Sleep quality improved in the HIIT group by 21.4%. Enjoyment improved by 7% and intrinsic motivation was increased by 13%. (5) Conclusions: We suggest that the 6-week HIIT program used in the present study is safe, since no severe hypoglycemia were reported, and an effective strategy in improving HRQoL, sleep quality, exercise motivation and enjoyment which are important psychological well-being factors in T1DM people.

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.

Central and Peripheral Oxygen Distribution in Two Different Modes of Interval Training

In high-intensity interval training the interval duration can be adjusted to optimize training results in oxygen uptake, cardiac output, and local oxygen supply. This study aimed to compare these variables in two interval trainings (long intervals HIIT3m: 3 min work, 3 min active rest vs. short intervals HIIT30s: 30 s work, 30 s active rest) at the same overall work rate and training duration. 24 participants accomplished both protocols, (work: 80% power output at VO₂peak, relief: 85% power output at gas exchange threshold) in randomized order. Spirometry, impedance cardiography, and near-infrared spectroscopy were used to analyze the physiological stress of the cardiopulmonary system and muscle tissue. Although times above gas exchange threshold were shorter in HIIT3m (HIIT3m 1669.9 ± 310.9 s vs. HIIT30s 1769.5 ± 189.0 s, p = 0.034), both protocols evoked similar average fractional utilization of VO₂peak (HIIT3m 65.23 ± 4.68% VO₂peak vs. HIIT30s 64.39 ± 6.78% VO₂peak, p = 0.261). However, HIIT3m resulted in higher cardiovascular responses during the loaded phases (VO₂p < 0.001, cardiac output p < 0.001). Local hemodynamics were not different between both protocols. Average physiological responses were not different in both protocols owning to incomplete rests in HIIT30s and large response amplitudes in HIIT3m. Despite lower acute cardiovascular stress in HIIT30s, short submaximal intervals may also trigger microvascular and metabolic adaptions similar to HIIT3m. Therefore, the adaption of interval duration is an important tool to adjust the goals of interval training to the needs of the athlete or patient.

The Effects of Exercise Order on the Psychophysiological Responses, Physical and Technical Performances of Young Soccer Players: Combined Small-Sided Games and High-Intensity Interval Training

This study aimed to compare the order effects of combined small-sided games (SSGs) and high-intensity interval training (HIIT) on the psychophysiological responses and physical and technical performances of young soccer players. Twenty-four soccer players (aged 14.63 ± 0.71 years) were randomly divided into SSGs + HIIT (n = 12) and HIIT + SSGs (n = 12) for 6 weeks. The SSGs consisted of two 4-16 min rounds of 2, 3, and four-a-side games with 2 min of passive resting, whereas the HIIT consisted of 6-10 min of high-intensity runs at varying intensities (from 90 to 100%). Pre-test and post-test elements included a 5-30 m sprint test, countermovement jump test, zigzag agility test with the ball and without the ball, repeated sprint ability test, speed dribbling ability test, three-corner run test, and Yo-Yo Intermittent Recovery Test level 1. Both combined training interventions produced similar improvements in physical performance and technical responses (p ≥ 0.05, d values ranging from 0.40 to 1.10). However, the combined HIIT + SSGs training produced meaningfully lower perceived exertion (p = 0.00, d = 2.98) and greater physical enjoyment (p = 0.00, d = 4.28) compared with the SSGs + HIIT intervention. Furthermore, the SSGs + HIIT group showed a higher training load than those from the HIIT + SSGs group for all weeks (p ≤ 0.05, d values ranging from 1.36 to 2.05). The present study's results might be used by coaches and practitioners to design training programmes for youth soccer players.

High-Intensity Conditioning for Combat Athletes: Practical Recommendations

Combat sports have been practiced for millennia and today are predominant sports at the Olympic games, with international organizations that host world, continental and national championships at amateur standard. There are also an increasing number of professional combat sports with global audiences. The growing popularity of professional combat sports and their importance at the Olympic games have led to an increase in scientific studies that characterize the physical, physiological, nutritional, biomechanical and training strategies of combat sports athletes. These studies characterize combat sports as high-intensity sports which require training strategies to develop the high-intensity capabilities of athletes. Therefore, the aim of this article is to (i) summarize the physiological demands of combat sports; (ii) present the primary considerations required to program high-intensity conditioning for athletes; (iii) define and present key high-intensity conditioning methods; and (iv) provide guidance for scientists and coaches to help prepare athletes under common but differing circumstances.

Cardiopulmonary Exercise Test Parameters in Athletic Population: A Review

Although still underutilized, cardiopulmonary exercise testing (CPET) allows the most accurate and reproducible measurement of cardiorespiratory fitness and performance in athletes. It provides functional physiologic indices which are key variables in the assessment of athletes in different disciplines. CPET is valuable in clinical and physiological investigation of individuals with loss of performance or minor symptoms that might indicate subclinical cardiovascular, pulmonary or musculoskeletal disorders. Highly trained athletes have improved CPET values, so having just normal values may hide a medical disorder. In the present review, applications of CPET in athletes with special attention on physiological parameters such as VO₂max, ventilatory thresholds, oxygen pulse, and ventilatory equivalent for oxygen and exercise economy in the assessment of athletic performance are discussed. The role of CPET in the evaluation of possible latent diseases and overtraining syndrome, as well as CPET-based exercise prescription, are outlined.

Training During the COVID-19 Lockdown: Knowledge, Beliefs, and Practices of 12,526 Athletes from 142 Countries and Six Continents

Objective

Our objective was to explore the training-related knowledge, beliefs, and practices of athletes and the influence of lockdowns in response to the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Methods

Athletes (n = 12,526, comprising 13% world class, 21% international, 36% national, 24% state, and 6% recreational) completed an online survey that was available from 17 May to 5 July 2020 and explored their training behaviors (training knowledge, beliefs/attitudes, and practices), including specific questions on their training intensity, frequency, and session duration before and during lockdown (March–June 2020).

Results

Overall, 85% of athletes wanted to “maintain training,” and 79% disagreed with the statement that it is “okay to not train during lockdown,” with a greater prevalence for both in higher-level athletes. In total, 60% of athletes considered “coaching by correspondence (remote coaching)” to be sufficient (highest amongst world-class athletes). During lockdown, < 40% were able to maintain sport-specific training (e.g., long endurance [39%], interval training [35%], weightlifting [33%], plyometric exercise [30%]) at pre-lockdown levels (higher among world-class, international, and national athletes), with most (83%) training for “general fitness and health maintenance” during lockdown. Athletes trained alone (80%) and focused on bodyweight (65%) and cardiovascular (59%) exercise/training during lockdown. Compared with before lockdown, most athletes reported reduced training frequency (from between five and seven sessions per week to four or fewer), shorter training sessions (from ≥ 60 to < 60 min), and lower sport-specific intensity (~ 38% reduction), irrespective of athlete classification.

Conclusions

COVID-19-related lockdowns saw marked reductions in athletic training specificity, intensity, frequency, and duration, with notable within-sample differences (by athlete classification). Higher classification athletes had the strongest desire to “maintain” training and the greatest opposition to “not training” during lockdowns. These higher classification athletes retained training specificity to a greater degree than others, probably because of preferential access to limited training resources. More higher classification athletes considered “coaching by correspondence” as sufficient than did lower classification athletes. These lockdown-mediated changes in training were not conducive to maintenance or progression of athletes’ physical capacities and were also likely detrimental to athletes’ mental health. These data can be used by policy makers, athletes, and their multidisciplinary teams to modulate their practice, with a degree of individualization, in the current and continued pandemic-related scenario. Furthermore, the data may drive training-related educational resources for athletes and their multidisciplinary teams. Such upskilling would provide athletes with evidence to inform their training modifications in response to germane situations (e.g., COVID related, injury, and illness).

Supplementary Information

The online version contains supplementary material available at 10.1007/s40279-021-01573-z.

Post-exercise energy intake: do the intensity and mode of exercise matter? A systematic review and meta-analysis comparing high-intensity interval with moderate-intensity continuous protocols

The present systematic review and meta-analysis aimed to compare the impact of exercise intensity and mode (high-intensity interval exercise-HIIE or sprint interval exercise-SIE versus moderate-intensity continuous exercise-MICE) on post-exercise ad libitum energy intake. The studies were required to have at least two exercise conditions (HIIE or SIE vs MICE). Overall, 642 manuscripts were initially identified and 17 met the eligibility criteria. The random effect meta-analysis did not reveal differences for absolute energy intake (28 pairwise comparisons) between HIIE (p = 0.54; 95% Confidence Interval - CI: -0.14 to 0.26; 22 pairwise comparisons) or SIE (p = 0.08; 95% CI -0.65 to 0.03; 6 pairwise comparisons) versus MICE, neither for relative energy intake (p = 0.97; 95% CI: -0.35 to 0.10 for HIIE; p = 0.28; 95% CI: -1.03 to 0.06 for SIE) with five and one pairwise comparisons, respectively. Subgroup analyses for methods to evaluate ad libitum energy intake, body mass, sex, volume, and timing of exercise were non-significant. Inspecting each study, two pairwise comparisons reported lower post-exercise absolute energy intake in HIIE compared to control (CRTL), and three pairwise comparisons reported lower absolute energy intake after SIE compared to MICE. None pairwise comparison reported differences between protocols (HIIE or SIE versus MICE) for relative energy intake. In conclusion, the meta-analysis did not show differences between protocols for absolute and relative energy intake; five pairwise comparisons from 28 demonstrated lower absolute energy intake in HIIE or SIE compared to CRTL or MICE. Further studies are needed to address the key relevant variables in which exercise intensity and mode may impact energy intake.

The Prediction of Running Velocity during the 30-15 Intermittent Fitness Test Using Accelerometry-Derived Metrics and Physiological Parameters: A Machine Learning Approach

Measuring exercise variables is one of the most important points to consider to maximize physiological adaptations. High-intensity interval training (HIIT) is a useful method to improve both cardiovascular and neuromuscular performance. The 30–15_IFT is a field test reflecting the effort elicited by HIIT, and the final velocity reached in the test is used to set the intensity of HIIT during the training session. In order to have a valid measure of the velocity during training, devices such as GPS can be used. However, in several situations (e.g., indoor setting), such devices do not provide reliable measures. The aim of the study was to predict exact running velocity during the 30–15_IFT using accelerometry-derived metrics (i.e., Player Load and Average Net Force) and heart rate (HR) through a machine learning (ML) approach (i.e., Support Vector Machine) with a leave-one-subject-out cross-validation. The SVM approach showed the highest performance to predict running velocity (r = 0.91) when compared to univariate approaches using PL (r = 0.62), AvNetForce (r = 0.73) and HR only (r = 0.87). In conclusion, the presented multivariate ML approach is able to predict running velocity better than univariate ones, and the model is generalizable across subjects.

Effect of Exercise Training on 1,25(OH)2D Levels: The FIT-AGEING Randomized Controlled Trial

BACKGROUND

Vitamin D deficiency is currently endemic worldwide and is considered as an important factor in the development of several chronic conditions. Physical exercise has been postulated as an auspicious strategy to counteract age-related disorders preventing premature mortality. However, the effects of chronic exercise training on 1,25-dihydroxyvitamin D [1,25(OH)₂D] is unclear. This 12-week randomized controlled trial aimed to investigate the effects of different training modalities on 1,25(OH)₂D in healthy sedentary adults.

HYPOTHESIS

Exercise training will increase 1,25(OH)₂D in the study cohort.

STUDY DESIGN

Randomized controlled clinical trial.

LEVEL OF EVIDENCE

Level 1.

METHODS

A total of 89 healthy sedentary adults (53% women; 53.5 ± 4.9 years old) were enrolled in the FIT-AGEING study. The participants were randomized to (1) a control group (no exercise), (2) physical activity recommendation from the World Health Organization (PAR group), (3) high-intensity interval training (HIIT group), and (4) HIIT adding whole-body electromyostimulation training (HIIT + EMS). 1,25(OH)₂D plasma levels were measured using a DiaSorin Liaison immunochemiluminometric analyzer.

RESULTS

Compared with the control group, 1,25(OH)₂D increased in PAR (Δ = 10.99 ± 3.44 pg/mL; P = 0.01), HIIT (Δ = 11.63 ± 3.51 pg/mL; P = 0.009), and HIIT + EMS groups (Δ = 14.01 ± 3.59 pg/mL; P = 0.001) without statistical differences between them (all Ps > 0.1).

CONCLUSION

In summary, the results show that a 12-week exercise intervention produced an increment of 1,25(OH)₂D independently of age, sex, and exercise modality in healthy sedentary adults.

CLINICAL RELEVANCE

The implementation of physical exercise could be considered a strategy not only aiming to reverse the seasonal decrease of 1,25(OH)₂D in winter explained by low sunlight exposure but also for obtaining subsequent increases of this hormone even in these a priori adverse conditions.

Effects of graded hypoxia during exhaustive intermittent cycling on subsequent exercise performance and neuromuscular responses

PURPOSE

This study examined the effect of graded hypoxia during exhaustive intermittent cycling on subsequent exercise performance and neuromuscular fatigue characteristics in normoxia.

METHODS

Fifteen well-trained cyclists performed an exhaustive intermittent cycling exercise (EICE 1; 15 s at 30% of anaerobic power reserve interspersed with 45 s of passive recovery) at sea level (SL; FiO₂ ~ 0.21), moderate (MH; FiO₂ ~ 0.16) and severe hypoxia (SH; FiO₂ ~ 0.12). This was followed, after 30 min of passive recovery in normoxia, by an identical exercise bout in normoxia (EICE 2). Neuromuscular function of the knee extensors was assessed at baseline, after EICE 1 (post-EICE 1), and EICE 2 (post-EICE 2).

RESULTS

The number of efforts completed decreased with increasing hypoxic severity during EICE 1 (SL: 39 ± 30, MH: 22 ± 13, SH: 13 ± 6; p ≤ 0.02), whereas there was no difference between conditions during EICE 2 (SL: 16 ± 9, MH: 20 ± 14, SH: 24 ± 17; p ≥ 0.09). Maximal torque (p = 0.007), peripheral (p = 0.02) and cortical voluntary activation (p < 0.001), and twitch torque (p < 0.001) decreased from baseline to post-EICE 1. Overall, there were no significant difference in any neuromuscular parameters from post-EICE 1 to post-EICE 2 (p ≥ 0.08).

CONCLUSION

Increasing hypoxia severity during exhaustive intermittent cycling hampered exercise capacity, but did not influence performance and associated neuromuscular responses during a subsequent bout of exercise in normoxia performed after 30 min of rest.

Exercise Training Protocols to Improve Obesity, Glucose Homeostasis, and Subclinical Inflammation

The global pandemics of obesity and sedentarism are associated with poor quality of life and increased risks for development of inflammatory chronic diseases, including type 2 diabetes, cardiovascular diseases, and cancer. Physical activity is considered as an antidote to counteract the development of chronic sterile inflammatory diseases. Thus, we review the most promising exercise training protocols for promoting weight loss, improving glucose homeostasis, and reducing inflammation. We discuss the advantages and disadvantages of moderate-intensity continuous aerobic training, high-intensity aerobic training, and combined (aerobic + resistance) training. Our aim with this chapter is to provide evidence and guidance for choosing the most appropriate protocols of exercise training according to the goals of the patient.

Applicability of Field Aerobic Fitness Tests in Soccer: Which One to Choose?

A desire to make fitness testing cheaper and easier to conduct in a team-sport setting has led to the development of numerous field aerobic fitness tests. This has contributed to a growing confusion among strength and conditioning coaches about which one to use. The main aim of this narrative review was to examine the reliability, validity, sensitivity and usefulness of the commonly used field aerobic fitness tests and to provide practical guidelines for their use in soccer. The University of Montreal track test (UMTT) and Vam Eval test seem the best options for estimation of maximal oxygen uptake (VO_2max) while the highest signal-to-noise ratio of the 30-15 intermittent fitness test (30-15IFT) suggests its superior sensitivity to track changes in fitness. The UMTT and 30-15IFT are the best solutions for prescription of long and short high-intensity interval training sessions, respectively. All field tests mostly present with marginal usefulness, but the smallest worthwhile change for UMTT or Vam Eval test, Yo-YoIRT2 and 30-15IFT are smaller than their stage increment making the improvement of only one stage in the test performance already worthwhile. Strength and conditioning coaches are advised to choose the test based on their specific purpose of testing.

Anaerobic Speed/Power Reserve and Sport Performance: Scientific Basis, Current Applications and Future Directions

Many individual and team sport events require extended periods of exercise above the speed or power associated with maximal oxygen uptake (i.e., maximal aerobic speed/power, MAS/MAP). In the absence of valid and reliable measures of anaerobic metabolism, the anaerobic speed/power reserve (ASR/APR) concept, defined as the difference between an athlete's MAS/MAP and their maximal sprinting speed (MSS)/peak power (MPP), advances our understanding of athlete tolerance to high speed/power efforts in this range. When exercising at speeds above MAS/MAP, what likely matters most, irrespective of athlete profile or locomotor mode, is the proportion of the ASR/APR used, rather than the more commonly used reference to percent MAS/MAP. The locomotor construct of ASR/APR offers numerous underexplored opportunities. In particular, how differences in underlying athlete profiles (e.g., fiber typology) impact the training response for different 'speed', 'endurance' or 'hybrid' profiles is now emerging. Such an individualized approach to athlete training may be necessary to avoid 'maladaptive' or 'non-responses'. As a starting point for coaches and practitioners, we recommend upfront locomotor profiling to guide training content at both the macro (understanding athlete profile variability and training model selection, e.g., annual periodization) and micro levels (weekly daily planning of individual workouts, e.g., short vs long intervals vs repeated sprint training and recovery time between workouts). More specifically, we argue that high-intensity interval training formats should be tailored to the locomotor profile accordingly. New focus and appreciation for the ASR/APR is required to individualize training appropriately so as to maximize athlete preparation for elite competition.

Effect of a Short HIIT Program with Specific Techniques on Physical Condition and Activity during Simulated Combat in National-Level Boxers

The present study investigated the effect of an additional short-duration HIIT program using boxing-specific techniques on activity during a simulated competition. Additionally, we investigated the impact on physical fitness, specifically aerobic performance and lower-body muscle power. Sixteen boxers were randomized into a control (n = 8) or experimental groups (n = 8). The experimental protocol consisted of 3 blocks of 5 repetitions of 30s all-out effort, with 6s recovery between repetitions and 1 min rest interval between blocks, conducted 3 days per week for 4 weeks. A two-way (group, two levels; moment, two levels) analysis of variance with repeated measurements in the second factor was used. For the experimental group, there was a change in body mass (ES = −0.13 (trivial)), body fat percentage (ES = −0.12 (trivial)), VO2max (ES = +0.42 (small)), CMJ (ES = +0.12 (trivial)), CMJ-left (ES = −0.11 (trivial)), CMJ-right (ES = +0.22 (trivial)), actions (ES = +0.68 (moderate)), time (ES = −0.29 (small)) and punches (ES = +0.56 (moderate)). For the control group, there was a change in body mass (ES = +0.04 (trivial)), body fat percentage (ES = −0.12 (trivial)), VO2max (ES = +0.11 (trivial)), CMJ (ES = −0.27 (small)), CMJ-left (ES = −0.39 (small)), CMJ-right (ES = +0.08 (trivial)), actions (ES = +0.08 (trivial)), time (ES = −0.65 (moderate)) and punches (ES = −0.57 (moderate)). The punches variable was significant concerning group-by-time interaction (F1,14 = 11.630; p = 0.004; n2 = 0.454). The present study indicated that the addition of a boxing-specific HIIT program is effective to increase the number of punches during a simulated match.

Physiological and performance responses of sprint interval training and endurance training in Gaelic football players

PURPOSE

While ideal for developing aerobic capacity, traditional endurance training (ET) is extremely time-consuming and may lack the specificity to maintain indices of speed and power in team sport athletes. In contrast, low-volume short-duration sprint interval training (SIT) has been shown to improve [Formula: see text]O2max to a similar extent as ET. However, to date, few studies have compared the effects of running-based SIT and ET, on aerobic capacity and indices of speed and power of trained team sport athletes.

METHODS

Club level male Gaelic football players were randomly assigned to SIT (n = 13; 26.5 ± 4.87 years) or ET (n = 12; 25.4 ± 2.58 years) groups. Participants trained 3 days week-1 for 6 weeks. [Formula: see text]O2max, RE, v[Formula: see text]O2max, blood lactate concentrations, Wingate test performance, running speed, jump performance and intermittent endurance performance (IEP) were measured at baseline and after 6 weeks.

RESULTS

An increase in [Formula: see text]O2max (p < 0.05), v[Formula: see text]O2max (p < 0.001) and IEP (p < 0.001) following 6 weeks of both SIT and ET was observed. Wingate mean power (p < 0.001), peak power (p < 0.001) and fatigue index (p < 0.005) were all significantly improved following training in both groups. Velocity at LT was significantly higher and performance in the 20-m running speed and VJ tests were significantly reduced post training in the ET group (all p < 0.005).

CONCLUSION

Despite the large difference in total training time, a running-based protocol of SIT is a time efficient training method for improving aerobic capacity and IEP while maintaining indices of lower body power and running speed in team-sport players.

High-Intensity Intermittent Exercise Performed on the Sand Induces Higher Internal Load Demands in Soccer Players

This study aimed to examine the acute physiological effect of shuttle-run-based high-intensity intermittent exercise (HIIE) performed at the same relative speed (i. e., 100% PS_T-CAR) on sand (SAND) and grass (GRASS) in male junior soccer players. Seven Under-23 Brazilian national league ("Série A") soccer players completed four testing sessions in either SAND or GRASS surface condition. The first two testing sessions consisted of performing a maximal progressive shuttle-run field protocol until volitional exhaustion (Carminatti's test, T-CAR), whereas the third and fourth sessions comprised a HIIE session on each ground surface. The HIIE session consisted of three 5-min bouts [12 s shuttle-run (with a direction change every 6 s)/12 s of passive rest] performed at 100% of T-CAR peak speed (PS_T-CAR) with 3 min of passive recovery between sets. Measurements of oxygen uptake (VO₂), heart rate (HR), blood lactate concentration ([La]), and rating of perceived exertion (RPE) were performed during all conditions. The SAND condition elicited significantly higher %VO₂peak (94.58 ± 2.73 vs. 87.45 ± 3.31%, p < 0.001, d = 2.35), %HRpeak (93.89 ± 2.63 vs. 90.31 ± 2.87%, p < 0.001, d = 1.30), RPE (8.00 ± 0.91 vs. 4.95 ± 1.23 a.u., p < 0.001, d = 2.82), and [La] (10.76 ± 2.37 vs. 5.48 ± 1.13 mmol/L, p < 0.010, d = 2.84). This study showed that higher internal workloads are experienced by the players during a single HIIE session performed on a softer surface as SAND, even when the exercise intensity was individualized based on 100%PS_T-CAR.

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

Engaging in regular exercise results in a range of physiological adaptations offering benefits for exercise capacity and health, independent of age, gender or the presence of chronic diseases. Accumulating evidence shows that lack of time is a major impediment to exercise, causing physical inactivity worldwide. This issue has resulted in momentum for interval training models known to elicit higher enjoyment and induce adaptations similar to or greater than moderate-intensity continuous training, despite a lower total exercise volume. Although there is no universal definition, high-intensity interval exercise is characterized by repeated short bursts of intense activity, performed with a "near maximal" or "all-out" effort corresponding to ≥90% of maximal oxygen uptake or >75% of maximal power, with periods of rest or low-intensity exercise. Research has indicated that high-intensity interval training induces numerous physiological adaptations that improve exercise capacity (maximal oxygen uptake, aerobic endurance, anaerobic capacity etc.) and metabolic health in both clinical and healthy (athletes, active and inactive individuals without any apparent disease or disorder) populations. In this paper, a brief history of high-intensity interval training is presented, based on the novel findings of some selected studies on exercise capacity and health, starting from the early 1920s to date. Further, an overview of the mechanisms underlying the physiological adaptations in response to high-intensity interval training is provided.

Brief Exercise at Work (BE@Work): A Mixed-Methods Pilot Trial of a Workplace High-Intensity Interval Training Intervention

Introduction: The efficacy of high-intensity interval training (HIIT) for improving markers of physical fitness and cardiometabolic health is promising. The workplace is one non-laboratory setting where the effectiveness of HIIT could be explored. The aim of this study was to undertake a mixed-methods exploratory pilot trial of a workplace HIIT intervention named Brief Exercise at Work (BE@Work). Methods: Fifty-four healthy employees (mean ± standard deviation [SD] age 46 ± 10 years) from two workplaces in Northeast England were allocated to 8 weeks of thrice-weekly workplace HIIT based on boxing, stair climbing and stepping, comprising 4-7 60 s high-intensity intervals interspersed with 75 s rest (n = 30), or a no-intervention control (n = 24). The primary outcome was the change SD of predicted maximal oxygen consumption (VO2max). Markers of physical fitness, cardiometabolic health and mental well-being were also measured at baseline and follow-up. Participant perceptions of the intervention were explored in post-intervention focus groups (n = 9). Results: Mean (±SD) session attendance was 82% (±15%). Mean peak heart rate across the intervention was 87% of age-predicted maximal heart rate with a within- and between-subject SD of 5.5% and 3.7%, respectively. The SD of changes in predicted VO2max was 6.6 mL·kg-1·min-1 across both groups, which can be used to inform sample size estimations for a future full trial. The control-adjusted mean increase (95% confidence interval) in predicted VO2max was 3.9 (-0.2 to 8.1) mL·kg-1·min-1, corresponding to a Cohen's D of 0.47. We also observed preliminary evidence of small to moderate effects in favour of the intervention group for non-dominant leg extensor muscle power, markers of health-related quality of life, well-being and perceived stress and small to moderate effects in favour of the controls in perceived pain, physical activity and high-density lipoprotein cholesterol. During HIIT, focus group participants reported physiological responses they perceived as unpleasant or tiring (e.g., breathlessness, local muscular fatigue), but also that they felt alert and energised afterwards. Conclusion: The findings of this exploratory pilot trial support the implementation of a definitive randomised controlled trial to quantify the effectiveness of a workplace HIIT intervention.

Test-retest reliability of the 30-15 Intermittent Fitness Test: A systematic review

PURPOSE

This review aimed to synthesize previous findings on the test-retest reliability of the 30-15 Intermittent Fitness Test (IFT).

METHODS

The literature searches were performed in 8 databases. Studies that examined the test-retest reliability of the 30-15 IFT and presented the intraclass correlation coefficient (ICC) and/or the coefficient of variation (CV) for maximal velocity and/or peak heart rate were included. The consensus-based standards for the selection of health measurement instruments (COSMIN) checklist was used for the assessment of the methodological quality of the included studies.

RESULTS

Seven studies, with a total of 10 study groups, explored reliability of maximal velocity assessed by the 30-15 IFT. ICCs ranged from 0.80 to 0.99, where 70% of ICCs were ≥0.90. CVs for maximal velocity ranged from 1.5% to 6.0%. Six studies, with a total of 7 study groups, explored reliability of peak heart rate as assessed by the 30-15 IFT. ICCs ranged from 0.90 to 0.97 (i.e., all ICCs were ≥0.90). CVs ranged from 0.6% to 4.8%. All included studies were of excellent methodological quality.

CONCLUSION

From the results of this systematic review, it can be concluded that the 30-15 IFT has excellent test-retest reliability for both maximal velocity and peak heart rate. The test may, therefore, be used as a reliable measure of fitness in research and sports practice.

VO2peak Response Heterogeneity in Persons with Multiple Sclerosis: To HIIT or Not to HIIT?

Exercise is described to provoke enhancements of cardiorespiratory fitness in persons with Multiple Sclerosis (pwMS). However, a high inter-individual variability in training responses has been observed. This analysis investigates response heterogeneity in cardiorespiratory fitness following high intensity interval (HIIT) and moderate continuous training (MCT) and analyzes potential predictors of cardiorespiratory training effects in pwMS. 131 pwMS performed HIIT or MCT 3-5x/ week on a cycle ergometer for three weeks. Individual responses were classified. Finally, a multiple linear regression was conducted to examine potential associations between changes of absolute peak oxygen consumption (absolute ∆V̇O_2peak/kg)_, training modality and participant's characteristics. Results show a time and interaction effect for ∆V̇O_2peak/kg. Absolute changes of cardiorespiratory responses were larger and the non-response proportions smaller in HIIT vs. MCT. The model accounting for 8.6% of the variance of ∆V̇O_2peak/kg suggests that HIIT, younger age and lower baseline fitness predict a higher absolute ∆V̇O_2peak/kg following an exercise intervention. Thus, this work implements a novel approach that investigates potential determinants of cardiorespiratory response heterogeneity within a clinical setting and analyzes a remarkable bigger sample. Further predictors need to be identified to increase the knowledge about response heterogeneity, thereby supporting the development of individualized training recommendations for pwMS.