Physical fitness and performance. Fatigue responses during repeated sprints matched for initial mechanical output

Comparative Effects of Two High-Intensity Intermittent Training Programs on Sub-Elite Male Basketball Referees' Fitness Levels

This study aimed to compare the effects of an 8-week short-term training program, comprising repeated sprints or running-based high-intensity intermittent training (HIIT), on the aerobic fitness and repeated sprint ability (RSA) performance of sub-elite basketball referees. Twenty male referees participated in supervised training sessions twice a week. They were randomly assigned to either the RSA-based group (RSAG) or the running-based HIIT group (HIITG). The RSAG conducted 3-4 sets of 8 × 20-m all-out sprints, while the HIITG performed 2-3 sets of 6 × 20-s runs at 90% of their maximal velocity achieved in the 30-15 intermittent fitness test (30-15IFT). Referees underwent a graded exercise test on a treadmill, the 30-15IFT, and an RSA test before and after the training program. Both groups showed significant improvement (~3%) in the fastest (22.6 ± 1.4 vs. 23.4 ± 1.7 and 22.0 ±1.9 vs. 22.4 ± 1.7 km·h-1 in RSAG and HIITG, respectively) and mean (21.5 ± 1.2 vs. 22.4 ± 1.4 and 21.3 ± 1.8 vs. 21.7 ± 1.6 km·h-1 in RSAG and HIITG, respectively) sprint velocity of the RSA test (p < 0.05). Moreover, positive changes (p < 0.05) were observed in the 30-15IFT maximal velocity (18.6 ± 1.1 vs. 19.3 ± 1.0 and 19.4 ± 0.9 vs. 20.5 ± 0.9 km·h-1 in RSAG and HIITG, respectively). In conclusion, an 8-week training intervention using either RSA or running-based HIIT led to similar improvements in referees' RSA performance and specific aerobic fitness measures. These findings could assist in devising tailored training programs for basketball referees.

Temporal patterns of fatigue in repeated sprint ability testing in soccer players and acute effects of different IHRs: a comparison between genders

BACKGROUND

Repeated sprint ability (RSA) in soccer is deemed fundamental to ensure high level of performance. The aim of this study was to investigate the acute effects of two different Initial Heart Rates (IHR) on fatigue when testing RSA in males and females' soccer players and to compare the respective patterns of fatigue.

METHODS

Nineteen female soccer players (age: 22.5±3.3 years, height 163.9±7.3 cm, body weight 54.3±6.4 kg, BMI 20.6±1.5 kg·m^-2) and 15 male soccer players (age: 17.9±1.5 years, height 175.9±5.8 cm, body weight 68.5±9.6 kg, BMI 22.3±1.5 kg·m^-2) participated in this study. HRs reached at the end of two different warm-up protocols (~90 vs. ~ 60% HR<inf>max</inf>), have been selected and the respective RSA performances were compared, within and between the groups of participants. Two sets of ten shuttle-sprints (15+15 m) with a 1:3 exercise to rest ratio with different IHR% were administered, in different days, in randomized order. To compare the different sprint performances, we employed the calculated Fatigue Index (FI%). Blood lactate concentration (BLa^-) was also measured before and after testing, to compare metabolic energy.

RESULTS

Significant differences among trials within each set (P<0.01) were found in both genders. Differences between sets were found in male players, (Factorial ANOVA 2x5; P<0.001), not in female. BLa^- after warm-up was higher in 90% vs. 60% HR<inf>max</inf> (P<0.05), in both genders but at the completion of RSA tests (after 3 minutes) the differences were not significant (P>0.05).

CONCLUSIONS

difference between genders were found, suggesting specific approach in testing and training RSA in soccer players.

Effects of Warm-Up Training on Psychomotor Vigilance and Repeated-Sprint Ability of Professional Soccer Referees: A Pilot Study

For this research, we analyzed the immediate effects of warm-up condition (WC) or without warm-up condition (WWC) on amateur referees' physical and cognitive functioning. Eight professional soccer referees from the Balearic Committee of Football Referees were the participants of this study. Body composition characteristics were measured and the scores on three tests were recorded: the Yo-Yo intermittent recovery, repeated-sprint ability, and psychomotor vigilance task. Regarding results, the psychomotor vigilance task was performed better after warm-up training (p = .002, η2 = .79) with faster reaction times following WC (M = 318.2, SD = 27.1 ms) than WWC (M = 334.9, SD = 26.1). Similarly, the referees' performance was better on the repeated-sprint ability test after WC (p = .002, d = 0.53) than WWC, with minimum and average power values higher after WC (M = 626.77, SD = 112.57) than WWC (M = 562.35, SD = 79.63). We conclude that re-warm-up training may mitigate the vigilance performance changes caused by effects of rest on soccer referees.

Evaluation of Neuromuscular Fatigue According to Injury History in a Repeat Sprint Ability Test, Countermovement Jump, and Hamstring Test in Elite Female Soccer Players

Sprinting is a fundamental component of the professional soccer player’s ability to achieve the highest performance in the sport. The aim of this study was to analyze the influence of hamstring injury history on the neuromuscular fatigue produced by an RSA test in elite female football players. Nineteen female elite soccer players of the Second Spanish Soccer Division participated in the study. The participants were divided into: (1) a Control group who have not suffered previous muscular injuries and (2) a Hamstring group with previous hamstring injury at least one season prior to the protocol. The players performed a protocol consisting of a Repeat Sprint Ability Test (RSA) (6 × 40 m; 30 s rest), and CMJ and Hamstring tests before and after the RSA. The different variables of the study were compared between groups with a two-way ANOVA for repeated measures. The main findings from the present study were that, in subjects with previous hamstring injury, the performance was impaired compared with the control group: (1) in the initial meters of the sprint during an RSA there was a higher percentage difference between SprintTT and ideal Split in 0–10 m compared to 0–20 m in the hamstring group (p = 0.006; ES = 0.51); and in situations of high fatigue there was a higher %Dif1vs6 compared to %Dif1vs5 (percentage difference between the first sprint and fifth sprint) in the hamstring group (p = 0.005; ES = 0.54) compared with the control group. It seems that in elite female soccer players with previous hamstring injury, RSA-induced fatigue produces a greater decrease in the performance in the first 10 m of the sprint compared to the control uninjured players.

The effect of fatigue on first stance phase kinetics during acceleration sprint running in professional football players

Nineteen professional football players (Age: 26±5 years; Height: 1.84±0.08 m; Mass: 83.4±8.9 kg) completed three x 30 m maximal acceleration sprints from a standing start before completing the Yo-Yo intermittent recovery test level 1. Three x 30 m maximal acceleration sprints were then repeated post-fatigue. Light gates recorded sprint times from 0-5 m, 0-10 m, 0-15 m and 0-30 m. Force platforms collected ground reaction force of the first stance phase of the sprint run. Differences between pre- and post-fatigue were observed in the sprint times over 0-15 m (P = 0.015; CI [0.007, 0.110]) and 0-30 m (P = 0.004; CI [0.056, 0.234]). Peak medial-lateral ground reaction force was lower (P = 0.045; CI [-0.146, -0.005]) post- than pre-fatigue. The ratio of force were significantly different between pre- and post-fatigue for the medial-lateral and anterior-posterior comparison (P = 0.017; CI [-0.063, -0.010]), and the medial-lateral and vertical comparison (P = 0.012; CI [-0.036, -0.007]). Football players altered their sprint mechanics to reduce medial-lateral loading and orient the force in an increased anteroposterior and vertical direction in order to maintain 0-10 m sprint performance. Practitioners should observe medial-lateral force contributions and improve sprint technical efficacy.

Effect of Vibration Massage and Passive Rest on Recovery of Muscle Strength after Short-Term Exercise

Background: The aim of the study was to compare the effect of vibration massage and passive rest on accelerating the process of muscle recovery after short-term intense exercise. Methods: Eighty-four healthy men aged 20 to 25 years participated in the study. Study participants performed isometric (ISO-M Group) and auxotonic (AUX-M group) contraction exercise in the lower limbs. Vibration massage was administered after exercise in the first recovery period. In the same period, controls rested passively, without the support of vibration massage. To assess the effectiveness of the applied vibration, a 4-fold measurement of the maximum force of the muscles involved in the exercise was performed under conditions of isometric contractions on a leg press machine set at an angle of 45° degrees upwards. Results: Differences in maximum strength during isometric contraction were found compared to baseline in favor of the groups subjected to the experimental vibration massage. Differences were demonstrated in muscle strength between the study groups (p < 0.005). The second period of passive rest in all groups did not bring significant changes in the values of maximal lower limb strength. Conclusions: Properly selected characteristics of the vibration effect can be an effective method in accelerating recovery and regaining lost motor capabilities of muscle groups fatigued by exercise. This offers the potential to shorten rest periods between sets of repetitions in training or between training units.

Effects of mild heat exposure on fatigue responses during two sets of repeated sprints matched for initial mechanical output

OBJECTIVES

We examined whether mild heat exposure alters performance, perceptual responses and neural drive to the quadriceps during two sets of repeated sprints matched for initial mechanical output.

DESIGN

Repeated measures.

METHODS

Twelve males performed 10 × 6-s sprints (recovery = 30 s), followed 6 min later by 5 × 6-s sprints (recovery = 30 s) in either COOL (24 °C/30% rH) or HOT (35 °C/40% rH) conditions. Subsequently, two sets of five consecutive sprints matched for initial mechanical output were compared.

RESULTS

On the basis of peak power, performance in sprint 2 was not significantly different to sprint 11 in both conditions (p ≥ 0.32). Average peak power across the five sprints compared (i.e., sprints 2-6 and 11-15, respectively) was 2.6 ± 3.4% higher in HOT compared to COOL (p = 0.025). Electromyographic activity (root mean square value) of the vastus lateralis muscle remained unchanged. Core (sprints 2-6: 37.85 ± 0.21 vs. 37.53 ± 0.19 °C, sprints 11-15: 38.26 ± 0.33 vs. 37.89 ± 0.24 °C; p < 0.001) and skin (sprints 2-6: 36.21 ± 0.29 vs. 30.72 ± 0.52 °C, sprints 11-15: 36.37 ± 0.28 vs. 30.99 ± 0.55 °C; p < 0.001) temperatures were overall higher in HOT compared to COOL. Heart rate, thermal sensation and comfort were significantly elevated in HOT compared to COOL (p ≤ 0.02), irrespective of sprint number.

CONCLUSIONS

When two sets of repeated sprints were matched for initial mechanical output, performance was enhanced with mild heat exposure. This occurred despite higher thermal, cardiovascular, and perceptual strain, and without alterations in quadriceps neural drive.

Neuromuscular fatigue of the elbow flexors during repeated maximal arm cycling sprints: the effects of forearm position

Repeated sprint exercise (RSE) is often used to induce neuromuscular fatigue (NMF). It is currently not known whether NMF is influenced by different forearm positions during arm cycling RSE. The purpose of this study was to investigate the effects of a pronated versus supinated forearm position on elbow flexor NMF during arm cycling RSE. Participants (n = 12) completed ten 10-s maximal arm cycling sprints interspersed by 60 s of rest on 2 separate days using either a pronated or supinated forearm position. All sprints were performed on an arm cycle ergometer in a reverse direction. Prior to and following RSE, NMF measurements (i.e., maximal voluntary contraction (MVC), potentiated twitch (PT), electromyography median frequencies) were recorded. Sprint performance measures, ratings of perceived exertion (RPE) and pain were also recorded. Irrespective of forearm position, sprint performance decreased as sprint number increased. These decreases were accompanied by significant increases in RPE (p < 0.001, ηp² = 0.869) and pain (p < 0.001, ηp² = 0.745). Participants produced greater power output during pronated compared with supinated sprinting (p < 0.001, ηp² = 0.728). At post-sprinting, the percentage decrease in elbow flexor MVC and PT force from pre-sprinting was significantly greater following supinated than pronated sprinting (p < 0.001), suggesting greater peripheral fatigue occurred in this position. The data suggest that supinated arm cycling RSE results in inferior performance and greater NMF compared with pronated arm cycling RSE. Novelty: NMF of the elbow flexors is influenced by forearm position during arm cycling RSE. Supinated arm cycling sprints resulted in worse repeated sprint performance and also greater NMF than pronated RSE.

Neuromuscular and perceptual responses during repeated cycling sprints-usefulness of a "hypoxic to normoxic" recovery approach

PURPOSE

We investigated the consequence of varying hypoxia severity during an initial set of repeated cycling sprints on performance, neuromuscular fatigability, and exercise-related sensations during a subsequent set of repeated sprints in normoxia.

METHODS

Nine active males performed ten 4-s sprints (recovery = 30 s) at sea level (SL; FiO₂ ~ 0.21), moderate (MH; FiO₂ ~ 0.17) or severe normobaric hypoxia (SH; FiO₂ ~ 0.13). This was followed, after 8 min of passive recovery, by five 4-s sprints (recovery = 30 s) in normoxia.

RESULTS

Mean power decrement during Sprint 10 was exacerbated in SH compared to SL and MH (- 34 ± 12%, - 22 ± 13%, - 25 ± 14%, respectively, p < 0.05). Sprint performance during Sprint 11 recovered to that of Sprint 1 in all conditions (p = 0.267). All exercise-related sensations at Sprint 11 recovered significantly compared to Sprint 1, with no difference for Set 2 (p > 0.05). Ratings of overall perceived discomfort, difficulty breathing, and limb discomfort were exacerbated during Set 1 in SH versus SL (p < 0.05). Compared to SL, the averaged MPO value for Set 2 was 5.5 ± 3.0% (p = 0.003) lower in SH. Maximal voluntary force and twitch torque decreased similarly in all conditions immediately after Set 1 (p < 0.05), without further alterations after Set 2. Peripheral and cortical voluntary activation values did not change (p > 0.05).

CONCLUSION

Exercise-related sensations, rather than neuromuscular function integrity, may play a pivotal role in influencing performance of repeated sprints and its recovery.

Acute effects of two different initial heart rates on testing the repeated sprint ability in elite women soccer players

BACKGROUND

Repeated sprint ability (RSA) in women's soccer is crucial to ensure high level of performance during the game. The aim of this study is to investigate the acute effects of two different initial heart rates intensities on fatigue when testing the RSA.

METHODS

Since there are many kinds of pre-match warming-ups, the heart rate reached at the end of two different warm-up protocols (~90 vs. ≈60% HRmax) as an indicator of internal load has been selected and the respective RSA performances were compared. RSA tests were performed by 19 elite women soccer players (age: 22.5±3.3 years, height 163.9±7.3 cm, body mass 54.3±6.4 kg, BMI 20.6±1.5 kg/m2) with two sets of ten shuttle-sprints (15+15 m) with a 1:3 exercise to rest ratio, in different days (randomized order) with different initial HR% (60% and 90% HRmax). In order to compare the different sprint performances a Fatigue Index (FI%) was computed; the blood lactate concentrations (BLa-) were measured before and after testing, to compare metabolic energy.

RESULTS

Significant differences among trials within each set (P<0.01) were found, as evidence of fatigue. Differences between sets were not found, (Factorial ANOVA 2x10; P>0.05). Although the BLa- after warm-up was higher between 90% vs. 60% HRmax (P<0.05), at the completion of RSA tests (after 3 minutes) the differences were considerably low and not significant (P>0.05).

CONCLUSIONS

This study shows that, contrary to male soccer, the initial heart rates, induced by different modes of warming-up, do not affect the overall performance while testing RSA in women's soccer players.

Maximal oxygen consumption and oxygen muscle saturation recovery following repeated anaerobic sprint test in youth soccer players

BACKGROUND

The purpose of the study was to examine whether differences in aerobic capacity (VO2max) influence muscle reoxygenation following repeated anaerobic sprint test (RAST) in soccer players. We hypothesized that muscle reoxygenation is faster in players with higher aerobic capacity.

METHODS

Ten male, youth soccer players participated in the study and performed RAST on a synthetic grass field. Oxygen saturation in muscle (StO2) of the right vastus lateralis muscle was measured by near-infrared spectroscopy. Half the time that was required for StO2 recovery (T1/2 StO2) after RAST was used to evaluate the reoxygenation in the recovery period after testing. The T1/2 StO2 was defined as the time from the end of RAST testing to the time of reaching 50% of StO2. Aerobic capacity (VO2max) was estimated by the Yo-Yo Intermittent Recovery Test level 1 (YYIR1).

RESULTS

The T1/2 StO2 had a significant inverse correlation with VO2max (r=-0.71; P=0.021) and with the distance which was covered by players on YYIR1 test (r=-0.71; P=0.021). In contrast, StO2 recovery rate showed no significant correlations with the VO2max in subjects.

CONCLUSIONS

These results indicate that aerobic capacity can influence vastus lateralis reoxygenation following RAST in youth soccer players.

Neuromuscular adaptations to sixteen weeks of whole-body high-intensity interval training compared to ergometer-based interval and continuous training

The neuromuscular adaptations between ergometer-based high-intensity interval training (HIIT-T; n = 15), whole-body high-intensity interval training (HIIT-WB; n = 12) and moderate-intensity continuous training (MICT; n = 14) were compared in forty-one healthy men randomized to 16 weeks of training (3x per week). Two-way repeated measures analysis of variance (ANOVA) showed countermovement (CMJ) and squat (SJ) jump height (HIIT-T: 8.5 ± 13.3%; 3.1 ± 9.7%, HIIT-WB: 6.4 ± 9.8%, 10.4 ± 16.1% and MICT: 2.2 ± 9.5%; 4.4 ± 12.1%, respectively), SJ peak power (HIIT-T: 1.7 ± 3.9%; HIIT-WB : 6.4 ± 7.9%; MICT: 0.5 ± 6.5%) and CMJ rate of force development (HIIT-T: 58.1 ± 50.5%; HIIT-WB: 36.9 ± 54.2%; MICT: 38.4 ± 64.3%) improved similarly in all training groups (all p < 0.05). CMJ peak power increased only after HIIT-T (4.3 ± 5.5%) and HIIT-WB (4.5 ± 5.2%), while no differences were observed in both the rectus femoris and vastus lateralis maximal electromyographic amplitude. Finally, marked improvements were also observed in the number of repetitions in the HIIT-WB protocol at the eighth week, with no further improvement at the sixteenth week. These data suggest that 16 weeks of HIIT-WB is capable to improve neuromuscular function to a similar extent as HIIT-T and MICT.

Effect of Prior Fatiguing Sport-Specific Exercise on Field Hockey Passing Ability

PURPOSE

To evaluate the effect of multiple sets of repeated-sprint-ability (RSA)-induced fatigue on subsequent passing-skill performance in field hockey players.

METHODS

A total of 10 elite U-21 (under-21) male field hockey players performed 5 sets of a combination of RSA test (6 × 20 m, 20 s of passive recovery) followed by a 1-min passing-skill test (passing reception with subsequent passes at a predesigned target). Data on fastest sprint time and cumulated sprint time for RSA test; total number of balls played, targeted, and passing accuracy (number of balls targeted/total number of balls played) for passing-skill test; heart rate (HR), blood lactate concentration (BLa), and rating of perceived exertion (RPE)  were collected throughout the protocol.

RESULTS

RSA performance was significantly impaired from set 1 to set 5 (fastest sprint time +4.1%, P < .001; cumulated sprint time +2.3%, P < .01). For a similar average number of balls played (12.8 [1.4]) during each set, number of balls targeted (-1.7%, P < .05) and passing accuracy (-3.1%, P < .05) decreased up to the third set before reimproving over the last 2 sets. Psychophysiological responses (HR, BLa, and RPE) progressively increased (P < .05) toward protocol cessation. The decrease in passing accuracy with increasing RSA cumulated sprint time was fitted to a 2nd-order polynomial function (r2 = .94, P < .05).

CONCLUSION

Multiple-set RSA-induced fatigue was accompanied by passing-skill adjustment variation, suggesting a complex interaction between physiological and psychological/cognitive function to preserve passing skill under fatigued condition.

Neuromuscular fatigue during repeated sprint exercise: underlying physiology and methodological considerations

Neuromuscular fatigue occurs when an individual’s capacity to produce force or power is impaired. Repeated sprint exercise requires an individual to physically exert themselves at near-maximal to maximal capacity for multiple short-duration bouts, is extremely taxing on the neuromuscular system, and consequently leads to the rapid development of neuromuscular fatigue. During repeated sprint exercise the development of neuromuscular fatigue is underlined by a combination of central and peripheral fatigue. However, there are a number of methodological considerations that complicate the quantification of the development of neuromuscular fatigue. The main goal of this review is to synthesize the results from recent investigations on the development of neuromuscular fatigue during repeated sprint exercise. Hence, we summarize the overall development of neuromuscular fatigue, explain how recovery time may alter the development of neuromuscular fatigue, outline the contributions of peripheral and central fatigue to neuromuscular fatigue, and provide some methodological considerations for quantifying neuromuscular fatigue during repeated sprint exercise.

Influences of Playing Position and Quality of Opposition on Standardized Relative Distance Covered in Domestic Women's Field Hockey: Implications for Coaches

Vinson, D, Gerrett, N, and James, DVB. Influences of playing position and quality of opposition on standardized relative distance covered in domestic women's field hockey: Implications for coaches. J Strength Cond Res 32(6): 1770-1777, 2018-The purpose of this study was to compare the standardized relative distance covered by the various playing positions (defenders, midfielders, and forwards) against different quality of opponents in domestic women's field hockey. Data were collected from 13 individuals competing for 1 team in the English Premier League across an 18-game season. Data were collected using portable global positioning system technology. Distance data were grouped into 6 speed zones relative to individual players' maximum sprint speeds and then standardized by dividing by the number of on-pitch minutes. Dependent variables included distance covered in the 6 speed zones, as well as the number of sprints and repeated sprint efforts (RSEs) completed in the highest speed zone. Participants covered a significantly greater total distance when competing against opponents from top 3 teams compared with middle 3 teams (111.78 ± 2.65 m·min vs. 107.35 ± 2.62 m·min, respectively). This was also true for distance covered in zone 4 (running) (29.47 ± 1.69 m·min vs. 27.62 ± 1.45 m·min, respectively) and zone 5 (fast running) (23.42 ± 1.76 m·min vs. 21.52 ± 1.79 m·min, respectively). Defenders (99.77 ± 4.36 m·min) covered significantly less total meters per minute than midfielders (117.20 ± 4.36 m·min) and completed significantly fewer RSEs per on-pitch minute (0.21 ± 0.03 and 0.33 ± 0.03, respectively). Midfielders covered significantly less distance in zone 2 (walking) than forwards (19.38 ± 1.64 m·min and 30.33 ± 2.12 m·min, respectively). Conversely, midfielders were shown to cover significantly more distance in zone 3 (jogging) than forwards (32.84 ± 1.10 m·min and 24.61 ± 1.42 m·min, respectively). A standardized and relative assessment may be useful for coaches' and performance analysts' understanding of players' performance in different positions or against different quality opponents.

Effects of short-term in-season break detraining on repeated-sprint ability and intermittent endurance according to initial performance of soccer player

To better understand the detraining effects in soccer, the purpose of the study was to analyse if performance level of soccer players modulate repeated-sprint ability (RSA) and intermittent endurance changes during 2-weeks of detraining (i.e., in-season break). Seventeen professional and sixteen young elite soccer players of two different teams performed, before and after 2-weeks of detraining, the RSA test and the Yo-Yo Intermittent Recovery Test, level 1 (YYIR1). Before detraining, professional players perform better (p < 0.05) RSA best time (RSA_best) than young players. A decrease (p < 0.05) in RSA_best, RSA total time (RSA_total) and mean time (RSA_mean) performance was observed in both teams, without changes in RSA fatigue index (Sdec). No significant changes in distance covered during YYIR1 was observed in any team. Before detraining, faster players from both teams (FG) (following the median split technique, soccer players with RSA_best ≤ 3.95 s) performed better (p < 0.01) in RSA_total, RSA_mean and RSA_best, but worse (p < 0.01) in Sdec. Although FG and the slower players (SG, RSA_best > 3.95 s) showed a worse (p < 0.05) RSA_total, RSA_best and RSA_mean performance after detraining (ES = 1.5, 1.4 and 2.9; ES = 0.6, 1.2 and 0.6; for FG and SG, respectively), the deterioration was greater in the FG for RSA_best (p < 0.05) and RSA_total (ES = 1.46). After detraining, FG improved (p < 0.05) Sdec performance. In conclusion, a 2-week in-season break (detraining) period induced a worse RSA, with no effect on intermittent endurance in professional and elite young soccer players, with greater detrimental effects on RSA_total and RSA_best in FG. In addition, Sdec does not seem to be sensitive to changes in RSA after a 2-week in-season break.

Interval running with self-selected recovery: Physiology, performance, and perception

This study (1) compared the physiological responses and performance during a high-intensity interval training (HIIT) session incorporating externally regulated (ER) and self-selected (SS) recovery periods and (2) examined the psychophysiological cues underpinning SS recovery durations. Following an incremental maximal exercise test to determine maximal aerobic speed (MAS), 14 recreationally active males completed 2 HIIT sessions on a non-motorised treadmill. Participants performed 12 × 30 s running intervals at a target intensity of 105% MAS interspersed with 30 s (ER) or SS recovery periods. During SS, participants were instructed to provide themselves with sufficient recovery to complete all 12 efforts at the required intensity. A semi-structured interview was undertaken following the completion of SS. Mean recovery duration was longer during SS (51 ± 15 s) compared to ER (30 ± 0 s; p < .001; d = 1.46 ± 0.46). Between-interval heart rate recovery was higher (SS: 19 ± 9 b min^-1; ER: 8 ± 5 b min^-1; p < .001; d = 1.43 ± 0.43) and absolute time ≥90% maximal heart rate (HR_max) was lower (SS: 335 ± 193 s; ER: 433 ± 147 s; p = .075; d = 0.52 ± 0.39) during SS compared to ER. Relative time ≥105% MAS was greater during SS (90 ± 6%) compared to ER (74 ± 20%; p < .01; d = 0.87 ± 0.40). Different sources of afferent information underpinned decision-making during SS. The extended durations of recovery during SS resulted in a reduced time ≥90% HR_max but enhanced time ≥105% MAS, compared with ER exercise. Differences in the afferent cue utilisation of participants likely explain the large levels of inter-individual variability observed.

Physical performance of elite and subelite Spanish female futsal players

The aim of this study was to determine the parameters distinguishing top female futsal players from lower level players. Twenty-seven female futsal players participated in the study, composed of professional first division (elite; n = 15) players and semi-professional second division players (sub-elite; n = 14). Active and passive straight leg raise tests, isokinetic strength of the knee extensor and flexor muscles at 60° · s(-1) angular velocity, squat and counter movement jumps, 30 m sprint, 30 m agility, repeated sprint ability test and maximum ball speed during shooting were measured. The elite players were more agile and kicked harder than sub-elite players in maximum ball speed during the shooting test (P ≤ 0.05). However, no significant differences between teams were observed in active and passive hamstring flexibility, jumping ability, repeated sprint ability test, 30 m sprint time, H/Q ratio and absolute and relative torque from 60° · s(-1) angular velocity. Based on these findings we conclude that agility and maximum ball speed during shooting may be important determinant factors of Spanish female futsal actions and could distinguish ability at high-level games.

Arm-cycling sprints induce neuromuscular fatigue of the elbow flexors and alter corticospinal excitability of the biceps brachii

We examined the effects of arm-cycling sprints on maximal voluntary elbow flexion and corticospinal excitability of the biceps brachii. Recreationally trained athletes performed ten 10-s arm-cycling sprints interspersed with 150 s of rest in 2 separate experiments. In experiment A (n = 12), maximal voluntary contraction (MVC) force of the elbow flexors was measured at pre-sprint 1, post-sprint 5, and post-sprint 10. Participants received electrical motor point stimulation during and following the elbow flexor MVCs to estimate voluntary activation (VA). In experiment B (n = 7 participants from experiment A), supraspinal and spinal excitability of the biceps brachii were measured via transcranial magnetic and transmastoid electrical stimulation that produced motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs), respectively, during a 5% isometric MVC at pre-sprint 1, post-sprint 1, post-sprint 5, and post-sprint 10. In experiment A, mean power output, MVC force, potentiated twitch force, and VA decreased 13.1% (p < 0.001), 8.7% (p = 0.036), 27.6% (p = 0.003), and 5.6% (p = 0.037), respectively, from pre-sprint 1 to post-sprint 10. In experiment B, (i) MEPs decreased 42.1% (p = 0.002) from pre-sprint 1 to post-sprint 5 and increased 40.1% (p = 0.038) from post-sprint 5 to post-sprint 10 and (ii) CMEPs increased 28.5% (p = 0.045) from post-sprint 1 to post-sprint 10. Overall, arm-cycling sprints caused neuromuscular fatigue of the elbow flexors, which corresponded with decreased supraspinal and increased spinal excitability of the biceps brachii. The different post-sprint effects on supraspinal and spinal excitability may illustrate an inhibitory effect on supraspinal drive that reduces motor output and, therefore, decreases arm-cycling sprint performance.

Neuro-mechanical determinants of repeated treadmill sprints - Usefulness of an "hypoxic to normoxic recovery" approach

To improve our understanding of the limiting factors during repeated sprinting, we manipulated hypoxia severity during an initial set and examined the effects on performance and associated neuro-mechanical alterations during a subsequent set performed in normoxia. On separate days, 13 active males performed eight 5-s sprints (recovery = 25 s) on an instrumented treadmill in either normoxia near sea-level (SL; FiO₂ = 20.9%), moderate (MH; FiO₂ = 16.8%) or severe normobaric hypoxia (SH; FiO₂ = 13.3%) followed, 6 min later, by four 5-s sprints (recovery = 25 s) in normoxia. Throughout the first set, along with distance covered [larger sprint decrement score in SH (−8.2%) compared to SL (−5.3%) and MH (−7.2%); P < 0.05], changes in contact time, step frequency and root mean square activity (surface electromyography) of the quadriceps (Rectus femoris muscle) in SH exceeded those in SL and MH (P < 0.05). During first sprint of the subsequent normoxic set, the distance covered (99.6, 96.4, and 98.3% of sprint 1 in SL, MH, and SH, respectively), the main kinetic (mean vertical, horizontal, and resultant forces) and kinematic (contact time and step frequency) variables as well as surface electromyogram of quadriceps and plantar flexor muscles were fully recovered, with no significant difference between conditions. Despite differing hypoxic severity levels during sprints 1–8, performance and neuro-mechanical patterns did not differ during the four sprints of the second set performed in normoxia. In summary, under the circumstances of this study (participant background, exercise-to-rest ratio, hypoxia exposure), sprint mechanical performance and neural alterations were largely influenced by the hypoxia severity in an initial set of repeated sprints. However, hypoxia had no residual effect during a subsequent set performed in normoxia. Hence, the recovery of performance and associated neuro-mechanical alterations was complete after resting for 6 min near sea level, with a similar fatigue pattern across conditions during subsequent repeated sprints in normoxia.

Effects of acute and 2-week administration of oral salbutamol on exercise performance and muscle strength in athletes

Our objective was to investigate effects of acute and 2-week administration of oral salbutamol on repeated sprint ability, exercise performance, and muscle strength in elite endurance athletes. Twenty male elite athletes [VO2max: 69.4 ± 1.8 (Mean ± SE) mL/min/kg], aged 25.9 ± 1.4 years, were included in a randomized, double-blinded and placebo-controlled parallel study. At baseline, after acute administration, and again after 2-week administration of the study drugs (8 mg salbutamol or placebo), subjects' maximal voluntary contraction (MVC) of m. quadriceps and isometric endurance of m. deltoideus were measured, followed by three repeated Wingate tests. Exercise performance at 110% of VO2max was determined on a bike ergometer. Acute administration of salbutamol increased peak power during first Wingate test by 4.1 ± 1.7% (P < 0.05). Two-week administration of salbutamol increased (P < 0.05) peak power during first and second Wingate test by 6.4 ± 2.0 and 4.2 ± 1.0%. Neither acute nor 2-week administration of salbutamol had any effect on MVC, exercise performance at 110% of VO2max or on isometric endurance. No differences were observed in the placebo group. In conclusion, salbutamol benefits athletes' sprint ability. Thus, the present study supports the restriction of oral salbutamol in competitive sports.

Determinants of team-sport performance: implications for altitude training by team-sport athletes

Team sports are increasingly popular, with millions of participants worldwide. Athletes engaged in these sports are required to repeatedly produce skilful actions and maximal or near-maximal efforts (eg, accelerations, changes in pace and direction, sprints, jumps and kicks), interspersed with brief recovery intervals (consisting of rest or low-intensity to moderate-intensity activity), over an extended period of time (1–2 h). While performance in most team sports is dominated by technical and tactical proficiencies, successful team-sport athletes must also have highly-developed, specific, physical capacities. Much effort goes into designing training programmes to improve these physical capacities, with expected benefits for team-sport performance. Recently, some team sports have introduced altitude training in the belief that it can further enhance team-sport physical performance. Until now, however, there is little published evidence showing improved team-sport performance following altitude training, despite the often considerable expense involved. In the absence of such studies, this review will identify important determinants of team-sport physical performance that may be improved by altitude training, with potential benefits for team-sport performance. These determinants can be broadly described as factors that enhance either sprint performance or the ability to recover from maximal or near-maximal efforts. There is some evidence that some of these physical capacities may be enhanced by altitude training, but further research is required to verify that these adaptations occur, that they are greater than what could be achieved by appropriate sea-level training and that they translate to improved team-sport performance.

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.

Emotional pictures impact repetitive sprint ability test on cycle ergometre

This study investigated the interaction between emotion-eliciting pictures and power output during a repetitive supra-maximal task on a cycle ergometre. Twelve male participants (mean (±SD) age, height and weight: 28.58 ± 3.23 years, 1.78 ± 0.05 m and 82.41 ± 13.29 kg) performed 5 repeated sprint tests on a cycle ergometre in front of neutral, pleasant or unpleasant pictures. For each sprint, mechanical (peak power and work), physiological (heart rate) and perceptual (affective load) indices were analysed. Affective load was calculated from the ratings of perceived exertion, which reflected the amount of pleasant and unpleasant responses experienced during exercise. The results showed that peak power, work and heart rate values were significantly lower (P < 0.05) for unpleasant pictures (9.18 ± 0.20 W ∙ kg(-1); 47.69 ± 1.08 J ∙ kg(-1); 152 ± 4 bpm) when compared with pleasant ones (9.50 ± 0.20 W ∙ kg(-1); 50.11 ± 0.11 J ∙ kg(-1); 156 ± 3 bpm). Furthermore, the affective load was found to be similar for the pleasant and unpleasant sessions. All together, these results suggested that the ability to produce maximal power output depended on whether the emotional context was pleasant or unpleasant. The fact that the power output was lower in the unpleasant versus pleasant session could reflect a regulatory process aimed at maintaining a similar level of affective load for both sessions.

Interaction of central and peripheral factors during repeated sprints at different levels of arterial O2 saturation

Purpose

To investigate the interaction between the development of peripheral locomotor muscle fatigue, muscle recruitment and performance during repeated-sprint exercise (RSE).

Method

In a single-blind, randomised and cross-over design, ten male team-sport athletes performed two RSE (fifteen 5-s cycling sprints interspersed with 25 s of rest; power self-selected) in normoxia and in acute moderate hypoxia (F_IO₂ 0.138). Mechanical work, total electromyographic intensity (summed quadriceps electromyograms, RMS_sum) and muscle (vastus lateralis) and pre-fontal cortex near-infrared spectroscopy (NIRS) parameters were calculated for every sprint. Blood lactate concentration ([Lac^-]) was measured throughout the protocol. Peripheral quadriceps fatigue was assessed via changes in potentiated quadriceps twitch force (ΔQ_tw,pot) pre- versus post-exercise in response to supra-maximal magnetic femoral nerve stimulation. The central activation ratio (Q_CAR) was used to quantify completeness of quadriceps activation.

Results

Compared with normoxia, hypoxia reduced arterial oxygen saturation (-13.7%, P=0.001), quadriceps RMS_sum (-13.7%, P=0.022), Q_CAR (-3.3%, P=0.041) and total mechanical work (-8.3%, P=0.019). However, the magnitude of quadriceps fatigue induced by RSE was similar in the two conditions (ΔQ_tw,pot: -53.5% and -55.1%, P=0.71). The lower cycling performance in hypoxia occurred despite similar metabolic (muscle NIRS parameters and blood [Lac^-]) and functional (twitch and M-wave) muscle states.

Conclusion

Results suggest that the central nervous system regulates quadriceps muscle recruitment and, thereby, performance to limit the development of muscle fatigue during intermittent, short sprints. This finding highlights the complex interaction between muscular perturbations and neural adjustments during sprint exercise, and further supports the presence of pacing during intermittent sprint exercise.

Neuromuscular adjustments of the quadriceps muscle after repeated cycling sprints

PURPOSE

This study investigated the supraspinal processes of fatigue of the quadriceps muscle in response to repeated cycling sprints.

METHODS

Twelve active individuals performed 10 × 6-s "all-out" sprints on a cycle ergometer (recovery = 30 s), followed 6 min later by 5 × 6-s sprints (recovery = 30 s). Transcranial magnetic and electrical femoral nerve stimulations during brief (5-s) and sustained (30-s) isometric contractions of the knee extensors were performed before and 3 min post-exercise.

RESULTS

Maximal strength of the knee extensors decreased during brief and sustained contractions (~11% and 9%, respectively; P<0.001). Peripheral and cortical voluntary activation, motor evoked potential amplitude and silent period duration responses measured during briefs contractions were unaltered (P>0.05). While cortical voluntary activation declined (P<0.01) during the sustained maximal contraction in both test sessions, larger reductions occurred (P<0.05) after exercise. Lastly, resting twitch amplitude in response to both femoral nerve and cortical stimulations was largely (> 40%) reduced (P<0.001) following exercise.

CONCLUSION

The capacity of the motor cortex to optimally drive the knee extensors following a repeated-sprint test was shown in sustained, but not brief, maximal isometric contractions. Additionally, peripheral factors were largely involved in the exercise-induced impairment in neuromuscular function, while corticospinal excitability was well-preserved.

Enhancing team-sport athlete performance: is altitude training relevant?

Field-based team sport matches are composed of short, high-intensity efforts, interspersed with intervals of rest or submaximal exercise, repeated over a period of 60-120 minutes. Matches may also be played at moderate altitude where the lower oxygen partial pressure exerts a detrimental effect on performance. To enhance run-based performance, team-sport athletes use varied training strategies focusing on different aspects of team-sport physiology, including aerobic, sprint, repeated-sprint and resistance training. Interestingly, 'altitude' training (i.e. living and/or training in O(2)-reduced environments) has only been empirically employed by athletes and coaches to improve the basic characteristics of speed and endurance necessary to excel in team sports. Hypoxia, as an additional stimulus to training, is typically used by endurance athletes to enhance performance at sea level and to prepare for competition at altitude. Several approaches have evolved in the last few decades, which are known to enhance aerobic power and, thus, endurance performance. Altitude training can also promote an increased anaerobic fitness, and may enhance sprint capacity. Therefore, altitude training may confer potentially-beneficial adaptations to team-sport athletes, which have been overlooked in contemporary sport physiology research. Here, we review the current knowledge on the established benefits of altitude training on physiological systems relevant to team-sport performance, and conclude that current evidence supports implementation of altitude training modalities to enhance match physical performances at both sea level and altitude. We hope that this will guide the practice of many athletes and stimulate future research to better refine training programmes.

Fatigue during intermittent-sprint exercise

1. There is a reversible decline in force production by muscles when they are contracting at or near their maximum capacity. The task-dependent nature of fatigue means that the mechanisms of fatigue may differ between different types of contractions. This paper examines how fatigue manifests during whole-body, intermittent-sprint exercise and discusses the potential muscular and neural mechanisms that underpin this fatigue. 2. Fatigue is defined as a reversible, exercise-induced reduction in maximal power output (e.g. during cycling exercise) or speed (e.g. during running exercise), even though the task can be continued. 3. The small changes in surface electromyogram (EMG), along with a lack of change in voluntary muscle activation (estimated from both percutaneous motor nerve stimulations and trans-cranial magnetic stimulation), indicate that there is little change in neural drive to the muscles following intermittent-sprint exercise. This, along with the observation that the decrease in EMG is much less than that which would be predicted from the decrease in power output, suggests that peripheral mechanisms are the predominant cause of fatigue during intermittent-sprint exercise. 4. At the muscle level, limitations in energy supply, including phosphocreatine hydrolysis and the degree of reliance on anaerobic glycolysis and oxidative metabolism, and the intramuscular accumulation of metabolic by-products, such as hydrogen ions, emerge as key factors responsible for fatigue.

Diminutions of acceleration and deceleration output during professional football match play

OBJECTIVES

This study examined distances covered at low (1-2 ms(-2)), moderate (2-3 ms(-2)) and high (>3 ms(-2)) acceleration (L(ACC), M(ACC) and H(ACC) respectively) and deceleration (L(DEC), M(DEC), and H(DEC) respectively) during competitive football games. Temporal and transient patterns of acceleration and deceleration were also examined.

DESIGN

Observational, repeated measures.

METHODS

Thirty-six professional male professional footballers were monitored using a 10 Hz non-differential global positioning system (NdGPS). Match data was organised into six 15 min periods (P1: 1-15 min, P2: 16-30 min, P3: 31-45 min, P4: 46-60 min, P5: 61-75 min, and P6: 76-90 min) for analysis of temporal patterns, and into eighteen 5 min periods for analysis of transient patterns. ANOVA with Bonferroni post hoc tests were used to identify significant (p<0.05) differences between periods.

RESULTS

Distance covered at L(ACC), M(ACC), H(ACC), L(DEC), M(DEC), and H(DEC) was 424±75 m, 242±25 m, 178±38 m, 365±54 m, 210±23 m and 162±29 m respectively. Between period decrements ranged from 8.0% to 13.2% from P1 to P3, 9.2% to 16.3% from P4 to P6, and from 14.9% to 21.0% from P1 to P6. Following PEAK H(ACC) (148% of mean 5 min H(ACC)), H(ACC) at 5POST was 10.4% lower than mean (p<0.01).

CONCLUSIONS

Time-dependent reductions in distances covered suggest that acceleration and deceleration capability are acutely compromised during match play. Further, the occurrence of transient fatigue may be supported by the findings that HACC and HDEC performance following PEAK was approximately 10% lower than mean values.

The recovery of repeated-sprint exercise is associated with PCr resynthesis, while muscle pH and EMG amplitude remain depressed

The physiological equivalents of power output maintenance and recovery during repeated-sprint exercise (RSE) remain to be fully elucidated. In an attempt to improve our understanding of the determinants of RSE performance we therefore aimed to determine its recovery following exhaustive exercise (which affected intramuscular and neural factors) concomitantly with those of intramuscular concentrations of adenosine triphosphate [ATP], phosphocreatine [PCr] and pH values and electromyography (EMG) activity (a proxy for net motor unit activity) changes. Eight young men performed 10, 6-s all-out sprints on a cycle ergometer, interspersed with 30 s of recovery, followed, after 6 min of passive recovery, by five 6-s sprints, again interspersed by 30 s of passive recovery. Biopsies of the vastus lateralis were obtained at rest, immediately after the first 10 sprints and after 6 min of recovery. EMG activity of the vastus lateralis was obtained from surface electrodes throughout exercise. Total work (TW), [ATP], [PCr], pH and EMG amplitude decreased significantly throughout the first ten sprints (P<0.05). After 6 min of recovery, TW during sprint 11 recovered to 86.3±7.7% of sprint 1. ATP and PCr were resynthesized to 92.6±6.0% and 85.3±10.3% of the resting value, respectively, but muscle pH and EMG amplitude remained depressed. PCr resynthesis was correlated with TW done in sprint 11 (r = 0.79, P<0.05) and TW done during sprints 11 to 15 (r = 0.67, P<0.05). There was a ∼2-fold greater decrease in the TW/EMG ratio in the last five sprints (sprint 11 to 15) than in the first five sprints (sprint 1 to 5) resulting in a disproportionate decrease in mechanical power (i.e., TW) in relation to EMG. Thus, we conclude that the inability to produce power output during repeated sprints is mostly mediated by intramuscular fatigue signals probably related with the control of PCr metabolism.

Hot conditions improve power output during repeated cycling sprints without modifying neuromuscular fatigue characteristics

This study investigated the effect of hot conditions on repeated sprint cycling performance and post-exercise alterations in isometric knee extension function. Twelve physically active participants performed 10 × 6-s "all-out" sprints on a cycle ergometer (recovery = 30 s), followed 6 min later by 5 × 6-s sprints (recovery = 30 s) in either a neutral (24 °C/30 %rH) or a hot (35 °C/40 %rH) environment. Neuromuscular tests including voluntary and electrically evoked isometric contractions of the knee extensors were performed before and after exercise. Average core temperature during exercise was higher (38.0 ± 0.1 vs. 37.7 ± 0.1 °C, respectively; P < 0.05) in hot versus neutral environments. Peak power output decreased (-17.9 % from sprint 1 to sprint 10 and -17.0 % from sprint 11 to sprint 15; P < 0.001) across repetitions. Average peak power output during the first ten sprints was higher (+3.1 %; P < 0.01) in the hot ambient temperature condition. Maximal strength (-12 %) and rate of force development (-15 to -26 %, 30-200 ms from the onset of contraction) decreased (P < 0.001) during brief contractions after exercise, irrespectively of the ambient temperature. During brief maximal contractions, changes in voluntary activation (~80 %) were not affected by exercise or temperature. Voluntary activation declined (P < 0.01) during the sustained contraction, with these reductions being more pronounced (P < 0.05) after exercise but not affected by the ambient temperature. Resting twitch amplitude declined (P < 0.001) by ~42 %, independently of the ambient temperature. In conclusion, heat exposure has no effect on the pattern and the extent of isometric knee extensor fatigue following repeated cycling sprints in the absence of hyperthermia.

Repeated-sprint ability - part II: recommendations for training

Short-duration sprints, interspersed with brief recoveries, are common during most team sports. The ability to produce the best possible average sprint performance over a series of sprints (≤10 seconds), separated by short (≤60 seconds) recovery periods has been termed repeated-sprint ability (RSA). RSA is therefore an important fitness requirement of team-sport athletes, and it is important to better understand training strategies that can improve this fitness component. Surprisingly, however, there has been little research about the best training methods to improve RSA. In the absence of strong scientific evidence, two principal training theories have emerged. One is based on the concept of training specificity and maintains that the best way to train RSA is to perform repeated sprints. The second proposes that training interventions that target the main factors limiting RSA may be a more effective approach. The aim of this review (Part II) is to critically analyse training strategies to improve both RSA and the underlying factors responsible for fatigue during repeated sprints (see Part I of the preceding companion article). This review has highlighted that there is not one type of training that can be recommended to best improve RSA and all of the factors believed to be responsible for performance decrements during repeated-sprint tasks. This is not surprising, as RSA is a complex fitness component that depends on both metabolic (e.g. oxidative capacity, phosphocreatine recovery and H+ buffering) and neural factors (e.g. muscle activation and recruitment strategies) among others. While different training strategies can be used in order to improve each of these potential limiting factors, and in turn RSA, two key recommendations emerge from this review; it is important to include (i) some training to improve single-sprint performance (e.g. 'traditional' sprint training and strength/power training); and (ii) some high-intensity (80-90% maximal oxygen consumption) interval training to best improve the ability to recover between sprints. Further research is required to establish whether it is best to develop these qualities separately, or whether they can be developed concurrently (without interference effects). While research has identified a correlation between RSA and total sprint distance during soccer, future studies need to address whether training-induced changes in RSA also produce changes in match physical performance.

Performance and fatigue during repeated sprints: what is the appropriate sprint dose?

When testing the ability of sportsmen to repeat maximal intensity efforts, or when designing specific training exercises to improve it, fatigue during repeated sprints is usually investigated through a number of sprints identical for all subjects, which induces a high intersubject variability in performance decrement in a typical heterogeneous group of athletes (e.g., team sport group, students, and research protocol volunteers). Our aim was to quantify the amplitude of the reduction in this variability when individualizing the sprint dose, that is, when requiring subjects to perform the number of sprints necessary to reach a target level of performance decrement. Fifteen healthy men performed 6-second sprints on a cycle ergometer with 24 seconds of rest until exhaustion or until 20 repetitions in case no failure occurred. Peak power output (PPO) was measured and a fatigue index (FI) computed. The variability in PPO decrement was compared between the 10th sprint and the sprint at which subject reached the target FI of 10%. Individual FI values after the 10th sprint were 14.6 ± 6.9 vs. 11.1 ± 1.2%, when individualizing the sprint dose, which corresponded to coefficients of interindividual variability of ∼47.3 and ∼10.8%, respectively. Individualizing the sprint dose substantially reduced intersubject variability in performance decrement, enabling a more standardized state of fatigue in repeated-sprints protocols designed to induce fatigue and test or train this specific repeated-sprint ability in a heterogeneous group of athletes. A direct feedback on the values of performance parameters is necessary between each sprint for the experimenter to set this individualized sprint dose.

Repeated-sprint ability - part I: factors contributing to fatigue

Short-duration sprints (<10 seconds), interspersed with brief recoveries (<60 seconds), are common during most team and racket sports. Therefore, the ability to recover and to reproduce performance in subsequent sprints is probably an important fitness requirement of athletes engaged in these disciplines, and has been termed repeated-sprint ability (RSA). This review (Part I) examines how fatigue manifests during repeated-sprint exercise (RSE), and discusses the potential underpinning muscular and neural mechanisms. A subsequent companion review to this article will explain a better understanding of the training interventions that could eventually improve RSA. Using laboratory and field-based protocols, performance analyses have consistently shown that fatigue during RSE typically manifests as a decline in maximal/mean sprint speed (i.e. running) or a decrease in peak power or total work (i.e. cycling) over sprint repetitions. A consistent result among these studies is that performance decrements (i.e. fatigue) during successive bouts are inversely correlated to initial sprint performance. To date, there is no doubt that the details of the task (e.g. changes in the nature of the work/recovery bouts) alter the time course/magnitude of fatigue development during RSE (i.e. task dependency) and potentially the contribution of the underlying mechanisms. At the muscle level, limitations in energy supply, which include energy available from phosphocreatine hydrolysis, anaerobic glycolysis and oxidative metabolism, and the intramuscular accumulation of metabolic by-products, such as hydrogen ions, emerge as key factors responsible for fatigue. Although not as extensively studied, the use of surface electromyography techniques has revealed that failure to fully activate the contracting musculature and/or changes in inter-muscle recruitment strategies (i.e. neural factors) are also associated with fatigue outcomes. Pending confirmatory research, other factors such as stiffness regulation, hypoglycaemia, muscle damage and hostile environments (e.g. heat, hypoxia) are also likely to compromise fatigue resistance during repeated-sprint protocols.

Dietary supplements and team-sport performance

A well designed diet is the foundation upon which optimal training and performance can be developed. However, as long as competitive sports have existed, athletes have attempted to improve their performance by ingesting a variety of substances. This practice has given rise to a multi-billion-dollar industry that aggressively markets its products as performance enhancing, often without objective, scientific evidence to support such claims. While a number of excellent reviews have evaluated the performance-enhancing effects of most dietary supplements, less attention has been paid to the performance-enhancing claims of dietary supplements in the context of team-sport performance. Dietary supplements that enhance some types of athletic performance may not necessarily enhance team-sport performance (and vice versa). Thus, the first aim of this review is to critically evaluate the ergogenic value of the most common dietary supplements used by team-sport athletes. The term dietary supplements will be used in this review and is defined as any product taken by the mouth, in addition to common foods, that has been proposed to have a performance-enhancing effect; this review will only discuss substances that are not currently banned by the World Anti-Doping Agency. Evidence is emerging to support the performance-enhancing claims of some, but not all, dietary supplements that have been proposed to improve team-sport-related performance. For example, there is good evidence that caffeine can improve single-sprint performance, while caffeine, creatine and sodium bicarbonate ingestion have all been demonstrated to improve multiple-sprint performance. The evidence is not so strong for the performance-enhancing benefits of β-alanine or colostrum. Current evidence does not support the ingestion of ribose, branched-chain amino acids or β-hydroxy-β-methylbutyrate, especially in well trained athletes. More research on the performance-enhancing effects of the dietary supplements highlighted in this review needs to be conducted using team-sport athletes and using team-sport-relevant testing (e.g. single- and multiple-sprint performance). It should also be considered that there is no guarantee that dietary supplements that improve isolated performance (i.e. single-sprint or jump performance) will remain effective in the context of a team-sport match. Thus, more research is also required to investigate the effects of dietary supplements on simulated or actual team-sport performance. A second aim of this review was to investigate any health issues associated with the ingestion of the more commonly promoted dietary supplements. While most of the supplements described in the review appear safe when using the recommended dose, the effects of higher doses (as often taken by athletes) on indices of health remain unknown, and further research is warranted. Finally, anecdotal reports suggest that team-sport athletes often ingest more than one dietary supplement and very little is known about the potential adverse effects of ingesting multiple supplements. Supplements that have been demonstrated to be safe and efficacious when ingested on their own may have adverse effects when combined with other supplements. More research is required to investigate the effects of ingesting multiple supplements (both on performance and health).

Relationship between different measures of aerobic fitness and repeated-sprint ability in elite soccer players

The main purpose of this study was to investigate the relationship between physiological variables related to aerobic fitness (maximal oxygen uptake: VO2max; the minimum velocity needed to reach VO2max: vVO2max; velocity at the onset of blood-lactate accumulation: vOBLA) and repeated sprint ability (RSA) in elite soccer players. Twenty-nine Brazilian soccer players (17.9 +/- 1.0 years; 178.7 +/- 5.2 cm; 73.6 +/- 6.7 kg; 11.1 +/- 1.3% body fat) from 2 national level teams (A, B) took part in the study. Subjects first performed an incremental test on a treadmill to determine their VO2max, vVO2max and vOBLA. After at least 48 hours, subjects performed an RSA test consisting of 7 34.2-m sprints interspersed with 25 seconds of active recovery, to determine the mean time (MT), the fastest time (FT) and the Sprint decrement (Sdec). Pearson product moment correlations and multiple regressions were used to assess the relationship between aerobic fitness and RSA variables (FT, MT, Sdec, [La] Peak). An analysis of variance, followed by a post hoc test (Tukey), was used to compare the 7 sprints of the RSA test. The level of significance was set at p < 0.05. A significant negative correlation was found between both vOBLA and vVO2max and MT during the RSA test (r = -0.49, p < 0.01; r = -0.38, p < 0.05, respectively). There were also negative correlations between Sdec and vOBLA (r = -0.54), vVO2max (r = -0.49) and VO2max (r = -0.39). The multiple regression revealed that the aerobic (vOBLA) and anaerobic (FT) components explained approximately 89% of the variance of MT. The results of this study demonstrated that RSA is more strongly correlated with vOBLA and vVO2max than the more commonly measured VO2max.

Maximal power, but not fatigability, is greater during repeated sprints performed in the afternoon

The present study was designed to investigate if the suggested greater fatigability during repeated exercise in the afternoon, compared to the morning, represents a true time-of-day effect on fatigability or a consequence of a higher initial power. In a counterbalanced order, eight subjects performed a repeated-sprint test [10 x (6 s of maximal cycling sprint + 30 s of rest)] on three different occasions between: 08:00-10:00, 17:00-19:00, and 17:00-19:00 h controlled (17:00-19:00 h(cont), i.e., initial power controlled to be the same as the two first sprints of the 08:00-10:00 h trial). Power output was significantly (p < 0.05) higher for sprints 1, 2, and 3 in the afternoon than in the morning (e.g., sprint 1: 23.3 +/-1 versus 21.2 +/-1 W.kg(-1)), but power decrement for the 10 sprints was also higher in the afternoon. Based on the following observations, we conclude that this higher power decrement is a consequence of the higher initial power output in the afternoon. First, there was no difference in power during the final five sprints (e.g., 20.4 +/-1 versus 19.7 +/-1 W.kg(-1) for sprint 10 in the afternoon and morning, respectively). Second, the greater decrement in the afternoon was no longer present when participants were producing the same initial power output in the afternoon as in the morning. Third, electromyographic activity of the vastus lateralis decreased during the exercise (p < 0.05), but without a time-of-day effect.

Effect of endurance training on performance and muscle reoxygenation rate during repeated-sprint running

The aim of the present study was to examine the effect of an 8-week endurance training program on repeated-sprint (RS) performance and post-sprints muscle reoxygenation rate in 18 moderately trained males (34 ± 5 years). Maximal aerobic speed (MAS), 10 km running and RS (2 × 15-s shuttle-sprints, interspersed with 15 s of passive recovery) performance were assessed before and after the training intervention. Total distance covered (TD) and the percentage of distance decrement (%Dec) were calculated for RS. Between-sprints muscle reoxygenation rate (Reoxy rate) was assessed with near-infrared spectroscopy during RS before and after training. After training, MAS (+9.8 ± 5.8%, with 100% chances to observe a substantial improvement), 10 km time (-6.2 ± 5.3%, 99%), TD (+9.6 ± 7.7%, 98%), %Dec (-25.6 ± 73.6%, 93%) and Reoxy rate (+152.4 ± 308.1%, 95%) were improved. The improvement of Reoxy rate was largely correlated with improvements in MAS [r = 0.63 (90% CL, 0.31;-0.82)] and %Dec [r = -0.52 (-0.15;-0.76)]. Present findings confirm the beneficial effect of endurance training on post-sprint muscle reoxygenation rate, which is likely to participate in the improvement of repeated-sprint ability after training. These data also confirm the importance of aerobic conditioning in sports, where repeating high-intensity/maximal efforts within a short time-period are required.