Speed endurance training is a powerful stimulus for physiological adaptations and performance improvements of athletes

Comparison between two types of anaerobic speed endurance training in competitive soccer players

The purpose of the present study was to examine the effects of additional in-season speed endurance production versus speed endurance maintenance training regimes on performance in competitive male soccer players. In a randomised controlled trial 18 male sub-elite players were exposed to additional speed endurance production (SEP) or speed endurance maintenance (SEM) training (two additional sessions/wk for 4 weeks) during the competitive season. Players performed the Yo-Yo intermittent recovery level 2 test (YYIR2) and a repeated sprint test (RST) pre- and post-intervention. Yo-Yo IR2 performance increased (p<0.001) by 50 ± 8% and 26 ± 5% in SEP and SEM, respectively, with greater (p=0.03) improvement in SEP. RST performance improved by 2.1 ± 0.3% and 1.3 ± 0.4% in SEP and SEM, respectively, while the RST fatigue index decreased (4.4 ± 0.8 to 3.4 ± 0.5%; p<0.04) in SEP only. Peak and average speed during training were higher (p<0.001) in SEP than in SEM (24.5 ± 0.3 vs 19.2 ± 0.3 and 15.5 ± 0.1 km·h-1 vs 9.4 ± 0.1 km·h-1). Additional in-season anaerobic speed endurance production and maintenance training improves high-intensity exercise performance in competitive soccer players with superior effects of speed endurance production training.

The Effect of Two Speed Endurance Training Regimes on Performance of Soccer Players

In order to better understand the specificity of training adaptations, we compared the effects of two different anaerobic training regimes on various types of soccer-related exercise performances. During the last 3 weeks of the competitive season, thirteen young male professional soccer players (age 18.5±1 yr, height 179.5±6.5 cm, body mass 74.3±6.5 kg) reduced the training volume by ~20% and replaced their habitual fitness conditioning work with either speed endurance production (SEP; n = 6) or speed endurance maintenance (SEM; n = 7) training, three times per wk. SEP training consisted of 6–8 reps of 20-s all-out running bouts followed by 2 min of passive recovery, whereas SEM training was characterized by 6–8 x 20-s all-out efforts interspersed with 40 s of passive recovery. SEP training reduced (p<0.01) the total time in a repeated sprint ability test (RSA_t) by 2.5%. SEM training improved the 200-m sprint performance (from 26.59±0.70 to 26.02±0.62 s, p<0.01) and had a likely beneficial impact on the percentage decrement score of the RSA test (from 4.07±1.28 to 3.55±1.01%) but induced a very likely impairment in RSA_t (from 83.81±2.37 to 84.65±2.27 s). The distance covered in the Yo-Yo Intermittent Recovery test level 2 was 10.1% (p<0.001) and 3.8% (p<0.05) higher after SEP and SEM training, respectively, with possibly greater improvements following SEP compared to SEM. No differences were observed in the 20- and 40-m sprint performances. In conclusion, these two training strategies target different determinants of soccer-related physical performance. SEP improved repeated sprint and high-intensity intermittent exercise performance, whereas SEM increased muscles’ ability to maximize fatigue tolerance and maintain speed development during both repeated all-out and continuous short-duration maximal exercises. These results provide new insight into the precise nature of a stimulus necessary to improve specific types of athletic performance in trained young soccer players.

Physiological and health-related adaptations to low-volume interval training: influences of nutrition and sex

Interval training refers to the basic concept of alternating periods of relatively intense exercise with periods of lower-intensity effort or complete rest for recovery. Low-volume interval training refers to sessions that involve a relatively small total amount of exercise (i.e. ≤10 min of intense exercise), compared with traditional moderate-intensity continuous training (MICT) protocols that are generally reflected in public health guidelines. In an effort to standardize terminology, a classification scheme was recently proposed in which the term 'high-intensity interval training' (HIIT) be used to describe protocols in which the training stimulus is 'near maximal' or the target intensity is between 80 and 100 % of maximal heart rate, and 'sprint interval training' (SIT) be used for protocols that involve 'all out' or 'supramaximal' efforts, in which target intensities correspond to workloads greater than what is required to elicit 100 % of maximal oxygen uptake (VO2max). Both low-volume SIT and HIIT constitute relatively time-efficient training strategies to rapidly enhance the capacity for aerobic energy metabolism and elicit physiological remodeling that resembles changes normally associated with high-volume MICT. Short-term SIT and HIIT protocols have also been shown to improve health-related indices, including cardiorespiratory fitness and markers of glycemic control in both healthy individuals and those at risk for, or afflicted by, cardiometabolic diseases. Recent evidence from a limited number of studies has highlighted potential sex-based differences in the adaptive response to SIT in particular. It has also been suggested that specific nutritional interventions, in particular those that can augment muscle buffering capacity, such as sodium bicarbonate, may enhance the adaptive response to low-volume interval training.

High intensity and reduced volume training attenuates stress and recovery levels in elite swimmers

This study investigated the effect of increased high-intensity interval training (HIT) at the expense of total training volume on the stress and recovery levels of elite swimmers. Forty-one elite swimmers participated in the study and were randomly assigned to either a HIT or a control group (CON). Eleven swimmers did not complete the questionnaires. For 12 weeks both groups trained ~12 h per week. The amount of HIT was ~5 h vs. 1 h, and total distance was ~17 km vs. ~35 km per week for HIT and CON, respectively. HIT was performed as 6-10 × 10-30 s maximal effort interspersed by 2-4 min of rest. The Recovery Stress Questionnaire - Sport was used to measure the swimmers' stress and recovery levels. After the 12 week intervention, the general stress level was 16.6% (2.6-30.7%; mean and 95% CI) lower and the general recovery level was 6.5% (0.7-12.4%) higher in HIT compared to the CON, after adjusting for baseline values. No significant effects could be observed in sports-specific stress or sports-specific recovery. The results indicate that increasing training intensity and reducing training volume for 12 weeks can reduce general stress and increase general recovery levels in competitive swimmers.

The effect of low-volume sprint interval training on the development and subsequent maintenance of aerobic fitness in soccer players

PURPOSE

To examine the effect of low-volume sprint interval training (SIT) on the development (part 1) and subsequent maintenance (part 2) of aerobic fitness in soccer players.

METHODS

In part 1, 23 players from the same semiprofessional team participated in a 2-wk SIT intervention (SIT, n = 14, age 25 ± 4 y, weight 77 ± 8 kg; control, n = 9, age 27 ± 6 y, weight 72 ± 10 kg). The SIT group performed 6 training sessions of 4-6 maximal 30-s sprints, in replacement of regular aerobic training. The control group continued with their regular training. After this 2-wk intervention, the SIT group was allocated to either intervention (n = 7, 1 SIT session/wk as replacement of regular aerobic training) or control (n = 7, regular aerobic training with no SIT sessions) for a 5-wk period (part 2). Pre and post measures were the YoYo Intermittent Recovery Test Level 1 (YYIRL1) and maximal oxygen uptake (VO2max).

RESULTS

In part 1, the 2-week SIT intervention had a small beneficial effect on YYIRL1 (17%; 90% confidence limits ±11%), and VO2max (3.1%; ±5.0%) compared with control. In part 2, 1 SIT session/wk for 5 wk had a small beneficial effect on VO2max (4.2%; ±3.0%), with an unclear effect on YYIRL1 (8%; ±16%).

CONCLUSION

Two weeks of SIT elicits small improvements in soccer players' high-intensity intermittent-running performance and VO2max, therefore representing a worthwhile replacement of regular aerobic training. The effectiveness of SIT for maintaining SIT-induced improvements in high-intensity intermittent running requires further research.

Cardiac parasympathetic reactivation following exercise: implications for training prescription

The objective of exercise training is to initiate desirable physiological adaptations that ultimately enhance physical work capacity. Optimal training prescription requires an individualized approach, with an appropriate balance of training stimulus and recovery and optimal periodization. Recovery from exercise involves integrated physiological responses. The cardiovascular system plays a fundamental role in facilitating many of these responses, including thermoregulation and delivery/removal of nutrients and waste products. As a marker of cardiovascular recovery, cardiac parasympathetic reactivation following a training session is highly individualized. It appears to parallel the acute/intermediate recovery of the thermoregulatory and vascular systems, as described by the supercompensation theory. The physiological mechanisms underlying cardiac parasympathetic reactivation are not completely understood. However, changes in cardiac autonomic activity may provide a proxy measure of the changes in autonomic input into organs and (by default) the blood flow requirements to restore homeostasis. Metaboreflex stimulation (e.g. muscle and blood acidosis) is likely a key determinant of parasympathetic reactivation in the short term (0-90 min post-exercise), whereas baroreflex stimulation (e.g. exercise-induced changes in plasma volume) probably mediates parasympathetic reactivation in the intermediate term (1-48 h post-exercise). Cardiac parasympathetic reactivation does not appear to coincide with the recovery of all physiological systems (e.g. energy stores or the neuromuscular system). However, this may reflect the limited data currently available on parasympathetic reactivation following strength/resistance-based exercise of variable intensity. In this review, we quantitatively analyse post-exercise cardiac parasympathetic reactivation in athletes and healthy individuals following aerobic exercise, with respect to exercise intensity and duration, and fitness/training status. Our results demonstrate that the time required for complete cardiac autonomic recovery after a single aerobic-based training session is up to 24 h following low-intensity exercise, 24-48 h following threshold-intensity exercise and at least 48 h following high-intensity exercise. Based on limited data, exercise duration is unlikely to be the greatest determinant of cardiac parasympathetic reactivation. Cardiac autonomic recovery occurs more rapidly in individuals with greater aerobic fitness. Our data lend support to the concept that in conjunction with daily training logs, data on cardiac parasympathetic activity are useful for individualizing training programmes. In the final sections of this review, we provide recommendations for structuring training microcycles with reference to cardiac parasympathetic recovery kinetics. Ultimately, coaches should structure training programmes tailored to the unique recovery kinetics of each individual.

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

High-intensity interval training (HIT) is a well-known, time-efficient training method for improving cardiorespiratory and metabolic function and, in turn, physical performance in athletes. HIT involves repeated short (<45 s) to long (2-4 min) bouts of rather high-intensity exercise interspersed with recovery periods (refer to the previously published first part of this review). While athletes have used 'classical' HIT formats for nearly a century (e.g. repetitions of 30 s of exercise interspersed with 30 s of rest, or 2-4-min interval repetitions ran at high but still submaximal intensities), there is today a surge of research interest focused on examining the effects of short sprints and all-out efforts, both in the field and in the laboratory. Prescription of HIT consists of the manipulation of at least nine variables (e.g. work interval intensity and duration, relief interval intensity and duration, exercise modality, number of repetitions, number of series, between-series recovery duration and intensity); any of which has a likely effect on the acute physiological response. Manipulating HIT appropriately is important, not only with respect to the expected middle- to long-term physiological and performance adaptations, but also to maximize daily and/or weekly training periodization. Cardiopulmonary responses are typically the first variables to consider when programming HIT (refer to Part I). However, anaerobic glycolytic energy contribution and neuromuscular load should also be considered to maximize the training outcome. Contrasting HIT formats that elicit similar (and maximal) cardiorespiratory responses have been associated with distinctly different anaerobic energy contributions. The high locomotor speed/power requirements of HIT (i.e. ≥95 % of the minimal velocity/power that elicits maximal oxygen uptake [v/p(·)VO(2max)] to 100 % of maximal sprinting speed or power) and the accumulation of high-training volumes at high-exercise intensity (runners can cover up to 6-8 km at v(·)VO(2max) per session) can cause significant strain on the neuromuscular/musculoskeletal system. For athletes training twice a day, and/or in team sport players training a number of metabolic and neuromuscular systems within a weekly microcycle, this added physiological strain should be considered in light of the other physical and technical/tactical sessions, so as to avoid overload and optimize adaptation (i.e. maximize a given training stimulus and minimize musculoskeletal pain and/or injury risk). In this part of the review, the different aspects of HIT programming are discussed, from work/relief interval manipulation to HIT periodization, using different examples of training cycles from different sports, with continued reference to the cardiorespiratory adaptations outlined in Part I, as well as to anaerobic glycolytic contribution and neuromuscular/musculoskeletal load.

Effects of 12 weeks high-intensity & reduced-volume training in elite athletes

It was investigated if high-intensity interval training (HIT) at the expense of total training volume improves performance, maximal oxygen uptake and swimming economy. 41 elite swimmers were randomly allocated to a control (CON) or HIT group. For 12 weeks both groups trained ∼12 h per week. HIT comprised ∼5 h vs. 1 h and total distance was ∼17 km vs. 35 km per week for HIT and CON, respectively. HIT was performed as 6-10×10-30 s maximal effort interspersed by 2–4 minutes of rest. Performance of 100 m all-out freestyle and 200 m freestyle was similar before and after the intervention in both HIT (60.4±4.0 vs. 60.3±4.0 s; n = 13 and 133.2±6.4 vs. 132.6±7.7 s; n = 14) and CON (60.2±3.7 vs. 60.6±3.8 s; n = 15 and 133.5±7.0 vs. 133.3±7.6 s; n = 15). Maximal oxygen uptake during swimming was similar before and after the intervention in both the HIT (4.0±0.9 vs. 3.8±1.0 l O₂×min⁻¹; n = 14) and CON (3.8±0.7 vs. 3.8±0.7 l O₂×min⁻¹; n = 11) group. Oxygen uptake determined at fixed submaximal speed was not significantly affected in either group by the intervention. Body fat % tended to increase (P = 0.09) in the HIT group (15.4±1.6% vs. 16.3±1.6%; P = 0.09; n = 16) and increased (P<0.05) in the CON group (13.9±1.5% vs. 14.9±1.5%; n = 17). A distance reduction of 50% and a more than doubled HIT amount for 12 weeks did neither improve nor compromise performance or physiological capacity in elite swimmers.

Performance effects of 6 weeks of aerobic production training in junior elite soccer players

This study investigates the performance effects of a 6-week biweekly anaerobic speed endurance production training among junior elite soccer players. Sixteen junior (age 16.9 ± 0.6 years) elite soccer players were tested in the Yo-Yo Intermittent Recovery test level 2 (IR2), 10-m and 35-m sprints, 7 × 35-m repeated-sprint ability (RSA) tests, countermovement jump and squat jump tests, and randomly assigned to either a control group (CG) performing their normal training schedule, which included 4 weekly soccer training sessions of approximately 90 minutes, or a training group performing anaerobic speed endurance production training twice weekly for 6 weeks in addition to their normal weekly schedule. We found that the intervention group significantly improved (p < 0.05) their performance in the Yo-Yo IR2 (63 ± 74 m) and 10-m sprint time (-0.06 ± 0.06 seconds). No significant performance changes were found in the CG. Between-group pretest to posttest differences were found for 10-m sprint times (p < 0.05). No significant changes were observed in the 35-m sprint times, RSA, or jump performances. These results indicate that short-term anaerobic production training is effective in improving acceleration and intermittent exercise performance among well-trained junior elite players.

Physiological response, time-motion characteristics, and reproducibility of various speed-endurance drills in elite youth soccer players: small-sided games versus generic running

PURPOSE

To quantify the physiological responses, time-motion characteristics, and reproducibility of various speed-endurance-production (SEP) and speed-endurance-maintenance (SEM) drills.

METHODS

Sixteen elite male youth soccer players completed 4 drills: SEP 1 v 1 small-sided game (SSG), SEP running drill, SEM 2 v 2 SSG, and SEM running drill. Heart-rate response, blood lactate concentration, subjective rating of perceived exertion (RPE), and time-motion characteristics were recorded for each drill.

RESULTS

The SEP and SEM running drills elicited greater (P < .05) heart-rate responses, blood lactate concentrations, and RPE than the respective SSGs (ES 1.1-1.4 and 1.0-3.2). Players covered less (P < .01) total distance and high-intensity distance in the SEP and SEM SSGs than in the respective running drills (ES 6.0-22.1 and 3.0-18.4). Greater distances (P < .01) were covered in high to maximum acceleration/deceleration bands during the SEP and SEM SSGs than the respective running drills (ES 2.6-4.6 and 2.3-4.8). The SEP SSG and generic running protocols produced greater (P < .05) blood lactate concentrations than the respective SEM protocols (ES 1.2-1.7). Small to moderate test-retest variability was observed for heart-rate response (CV 0.9-1.9%), RPE (CV 2.9-5.7%), and blood lactate concentration (CV 9.9-14.4%); moderate to large test-retest variability was observed for high-intensity-running parameters (CV > 11.3%) and the majority of accelerations/deceleration distances (CV > 9.8%) for each drill.

CONCLUSIONS

The data demonstrate the potential to tax the anaerobic energy system to different extents using speed-endurance SSGs and that SSGs elicit greater acceleration/ deceleration load than generic running drills.

Changes of direction during high-intensity intermittent runs: neuromuscular and metabolic responses

BACKGROUND

The ability to sustain brief high-intensity intermittent efforts (HIE) is meant to be a major attribute for performance in team sports. Adding changes of direction to HIE is believed to increase the specificity of training drills with respect to game demands. The aim of this study was to investigate the influence of 90°-changes of direction (COD) during HIE on metabolic and neuromuscular responses.

METHODS

Eleven male, team sport players (30.5 ± 3.6 y) performed randomly HIE without (straight-line, 2×[10× 22 m]) or with (2×[10× ~16.5 m]) two 90°-COD. To account for the time lost while changing direction, the distance for COD runs during HIE was individually adjusted using the ratio between straight-line and COD sprints. Players also performed 2 countermovement (CMJ) and 2 drop (DJ) jumps, during and post HIE. Pulmonary oxygen uptake (VO2), quadriceps and hamstring oxygenation, blood lactate concentration (Δ[La]b), electromyography amplitude (RMS) of eight lower limb muscles and rating of perceived exertion (RPE) were measured for each condition.

RESULTS

During HIE, CODs had no substantial effects on changes in VO2, oxygenation, CMJ and DJ performance and RPE (all differences in the changes rated as unclear). Conversely, compared with straight-line runs, COD-runs were associated with a possibly higher Δ[La]b (+9.7 ± 10.4%, with chances for greater/similar/lower values of 57/42/0%) and either a lower (i.e., -11.9 ± 14.6%, 2/13/85 for semitendinosus and -8.5 ± 9.3%, 1/21/78 for lateral gastrocnemius) or equivalent decrease in electromyography amplitude.

CONCLUSION

Adding two 90°-CODs on adjusted distance during two sets of HIE is likely to elicit equivalent decreases in CMJ and DJ height, and similar cardiorespiratory and perceptual responses, despite a lower average running speed. A fatigue-induced modification in lower limb control observed with CODs may have elicited a selective reduction of electromyography activity in hamstring muscles and may induce, in turn, a potential mechanical loss of knee stability. Therefore, changing direction during HIE, with adjusted COD running distances, might be an effective training practice 1) to manipulate some components of the acute physiological load of HIE, 2) to promote long-term COD-specific neuromuscular adaptations aimed at improving performance and knee joint stability.

High-intensity interval training, solutions to the programming puzzle: Part I: cardiopulmonary emphasis

High-intensity interval training (HIT), in a variety of forms, is today one of the most effective means of improving cardiorespiratory and metabolic function and, in turn, the physical performance of athletes. HIT involves repeated short-to-long bouts of rather high-intensity exercise interspersed with recovery periods. For team and racquet sport players, the inclusion of sprints and all-out efforts into HIT programmes has also been shown to be an effective practice. It is believed that an optimal stimulus to elicit both maximal cardiovascular and peripheral adaptations is one where athletes spend at least several minutes per session in their 'red zone,' which generally means reaching at least 90% of their maximal oxygen uptake (VO2max). While use of HIT is not the only approach to improve physiological parameters and performance, there has been a growth in interest by the sport science community for characterizing training protocols that allow athletes to maintain long periods of time above 90% of VO2max (T@VO2max). In addition to T@VO2max, other physiological variables should also be considered to fully characterize the training stimulus when programming HIT, including cardiovascular work, anaerobic glycolytic energy contribution and acute neuromuscular load and musculoskeletal strain. Prescription for HIT consists of the manipulation of up to nine variables, which include the work interval intensity and duration, relief interval intensity and duration, exercise modality, number of repetitions, number of series, as well as the between-series recovery duration and intensity. The manipulation of any of these variables can affect the acute physiological responses to HIT. This article is Part I of a subsequent II-part review and will discuss the different aspects of HIT programming, from work/relief interval manipulation to the selection of exercise mode, using different examples of training cycles from different sports, with continued reference to T@VO2max and cardiovascular responses. Additional programming and periodization considerations will also be discussed with respect to other variables such as anaerobic glycolytic system contribution (as inferred from blood lactate accumulation), neuromuscular load and musculoskeletal strain (Part II).

Yo-Yo intermittent recovery test performances within an entire football league during a full season

The study examined Yo-Yo intermittent recovery level 2 (YYIR2) and submaximal YYIR1 test performances in 172 male semi-professional football players (age; 25.8 ± 4.1 years) representing all teams in a top league at pre-season, start-season, mid-season and end-season. YYIR2 performance was 847 ± 227 m (±SD) at pre-season and rose (P < 0.05) by 128 ± 113 m to 975 ± 205 m at start of season and further (P < 0.05) by 59 ± 102 m to 1034 ± 211 m at mid-season. Submaximal YYIR1 HR was 90.9 ± 4.2% HR(max) at pre-season, which was higher (P < 0.05) than at start, mid and end of season (87.0 ± 3.9, 85.9 ± 4.1 and 87.0 ± 3.7% HR(max), respectively). Peak YYIR2 performance and minimum YYIR1 HR were 1068 ± 193 m and 85.1 ± 3.8% HR(max), respectively, with ~50% of the players peaking at mid-season. Top-teams and middle-teams had higher (P < 0.05) peak YYIR2 scores (1094 ± 205 and 1121 ± 152 m, respectively) than bottom-teams (992 ± 185 m). YYIR2 performance was 16% higher (P < 0.05) and YYIR1 HR was 1.4% HR(max) lower (P < 0.05) for regular players than non-regular players at pre-season and remained lower (P < 0.05) throughout the season. Central defenders had poorer (P < 0.05) YYIR performances compared to other positional roles. In conclusion, YYIR performances are highly variable within a football league over a season and are influenced by league ranking, regularity of competitive play and playing position.

Efeito da intensidade do exercício de corrida intermitente 30s:15s no tempo de manutenção no ou próximo do VO2max

O presente estudo comparou o tempo mantido acima de 90% (t90VO2max) e de 95% VO2max (t95VO2max) em três diferentes intensidades de exercício. Após a realização de um teste incremental para determinar o VO2max, oito estudantes de educação física ativos (23 ± 3 anos) executaram três sessões de exercícios intermitentes (100, 110 e 120% da velocidade do VO2max (vVO2max)) com razão esforço:recuperação de 30s:15s. O t95VO2max foi significantemente maior em 110%vVO2max (EI110%) (218,1 ± 81,6 s) quando comparado a 100%vVO2max (EI100%) (91,9 ± 75,2s) e a 120%vVO2max (EI120%) (126,3 ± 29,4 s), porém sem diferença entre EI100% e EI120%. O t90VO2max somente apresentou diferença significante entre EI110% e EI120%. Portanto, conclui-se que durante exercício intermitente com razão 30s:15s, a intensidade de 110%vVO2max apresenta-se mais adequada para manter o VO2 próximo ou no VO2max por um tempo maior.

The 10-20-30 training concept improves performance and health profile in moderately trained runners

The effect of an alteration from regular endurance to interval (10-20-30) training on the health profile, muscular adaptations, maximum oxygen uptake (V̇o2max), and performance of runners was examined. Eighteen moderately trained individuals (6 females and 12 males; V̇o2max: 52.2 ± 1.5 ml·kg−1·min−1) (means ± SE) were divided into a high-intensity training (10-20-30; 3 women and 7 men) and a control (CON; 3 women and 5 men) group. For a 7-wk intervention period the 10-20-30 replaced all training sessions with 10-20-30 training consisting of low-, moderate-, and high-speed running (<30%, <60%, and >90% of maximal intensity) for 30, 20, and 10 s, respectively, in three or four 5-min intervals interspersed by 2 min of recovery, reducing training volume by 54% (14.0 ± 0.9 vs. 30.4 ± 2.3 km/wk) while CON continued the normal training. After the intervention period V̇o2max in 10-20-30 was 4% higher, and performance in a 1,500-m and a 5-km run improved ( P < 0.05) by 21 and 48 s, respectively. In 10-20-30, systolic blood pressure was reduced ( P < 0.05) by 5 ± 2 mmHg, and total and low-density lipoprotein (LDL) cholesterol was lowered ( P < 0.05) by 0.5 ± 0.2 and 0.4 ± 0.1 mmol/l, respectively. No alterations were observed in CON. Muscle membrane proteins and enzyme activity did not change in either of the groups. The present study shows that interval training with short 10-s near-maximal bouts can improve performance and V̇o2max despite a ∼50% reduction in training volume. In addition, the 10-20-30 training regime lowers resting systolic blood pressure and blood cholesterol, suggesting a beneficial effect on the health profile of already trained individuals.

Effects of physical activity and inactivity on muscle fatigue

The aim of this review was to examine the mechanisms by which physical activity and inactivity modify muscle fatigue. It is well known that acute or chronic increases in physical activity result in structural, metabolic, hormonal, neural, and molecular adaptations that increase the level of force or power that can be sustained by a muscle. These adaptations depend on the type, intensity, and volume of the exercise stimulus, but recent studies have highlighted the role of high intensity, short-duration exercise as a time-efficient method to achieve both anaerobic and aerobic/endurance type adaptations. The factors that determine the fatigue profile of a muscle during intense exercise include muscle fiber composition, neuromuscular characteristics, high energy metabolite stores, buffering capacity, ionic regulation, capillarization, and mitochondrial density. Muscle fiber-type transformation during exercise training is usually toward the intermediate type IIA at the expense of both type I and IIx myosin heavy-chain isoforms. High-intensity training results in increases of both glycolytic and oxidative enzymes, muscle capillarization, improved phosphocreatine resynthesis and regulation of K⁺, H⁺, and lactate ions. Decreases of the habitual activity level due to injury or sedentary lifestyle result in partial or even compete reversal of the adaptations due to previous training, manifested by reductions in fiber cross-sectional area, decreased oxidative capacity, and capillarization. Complete immobilization due to injury results in markedly decreased force output and fatigue resistance. Muscle unloading reduces electromyographic activity and causes muscle atrophy and significant decreases in capillarization and oxidative enzymes activity. The last part of the review discusses the beneficial effects of intermittent high-intensity exercise training in patients with different health conditions to demonstrate the powerful effect of exercise on health and well being.

Physiological adaptations to low-volume, high-intensity interval training in health and disease

Exercise training is a clinically proven, cost-effective, primary intervention that delays and in many cases prevents the health burdens associated with many chronic diseases. However, the precise type and dose of exercise needed to accrue health benefits is a contentious issue with no clear consensus recommendations for the prevention of inactivity-related disorders and chronic diseases. A growing body of evidence demonstrates that high-intensity interval training (HIT) can serve as an effective alternate to traditional endurance-based training, inducing similar or even superior physiological adaptations in healthy individuals and diseased populations, at least when compared on a matched-work basis. While less well studied, low-volume HIT can also stimulate physiological remodelling comparable to moderate-intensity continuous training despite a substantially lower time commitment and reduced total exercise volume. Such findings are important given that 'lack of time' remains the most commonly cited barrier to regular exercise participation. Here we review some of the mechanisms responsible for improved skeletal muscle metabolic control and changes in cardiovascular function in response to low-volume HIT. We also consider the limited evidence regarding the potential application of HIT to people with, or at risk for, cardiometabolic disorders including type 2 diabetes. Finally, we provide insight on the utility of low-volume HIT for improving performance in athletes and highlight suggestions for future research.