A Standardized Small Sided Game Can Be Used to Monitor Neuromuscular Fatigue in Professional A-League Football Players

ArticleinFrontiers in Physiology 9 · August 2018with 172 Reads
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Abstract
Introduction: Training and competition load can cause neuromuscular fatigue (NMF) and modified movement strategy such as an increase in the contribution of the medio-lateral [PlayerLoadTMML(%)] and decrease in the % vertical [PlayerLoadTMV(%)] vectors, to total PlayerLoadTM (accelerometer derived measurement in vertical, medio-lateral, and anterior-posterior planes) in matches. NMF assessment involves expensive equipment, however, given the modification of match movement strategy with NMF, this may be present in a standardized drill. The aim of this study was to determine the utility of a small sided game (SSG) for the measurement of NMF. Materials and Methods: Data was collected throughout a competitive football season. External load was quantified using global positioning system (GPS) and accelerometry, and internal load by session rating of perceived exertion (sRPE). A 5 vs. 5 SSG and countermovement jump (CMJ), for determination of flight time:contraction time (FT:CT), were performed the day prior to each match. Weekly volume from GPS, PlayerLoadTM and sRPE were calculated across the season. Weekly SSG activity profile and FT:CT was compared between “high” and “low” load weeks determined relative to season average. SSG activity profile was assessed between weeks where FT:CT was above or below pre-season baseline. Impact on match activity profile was examined between weeks where FT:CT and SSG activity profile were higher or lower than baseline. The difference (high vs. low load and < or > pre-season baseline) was calculated using the effect size (ES) ± 90% CI and practically important if there was a >75% likelihood of exceeding an ES of 0.2. Results: All weekly load metrics increased SSG PlayerLoadTM⋅m⋅min⁻¹ when above season average, however, the impact on FT:CT was trivial. Reduced weekly FT:CT compared to baseline resulted in lower SSG PlayerLoadTM⋅min⁻¹ and PlayerLoadTMSlow⋅min⁻¹. FT:CT below baseline increased match PlayerLoadTMML(%) and decreased PlayerLoadTMV(%) during subsequent match play. Similarly, a reduction in SSG PlayerLoadTM⋅m⋅min⁻¹ was followed by increased match PlayerLoadTMML(%). Conclusion: Changes in select match activity profile variables following a reduction in SSG PlayerLoadTM m.min⁻¹, mirror those seen when FT:CT is reduced. Increased PlayerLoadTMML(%) during matches likely represents fatigue driven modification to movement strategy. Small-sided games may be a useful tool to detect NMF.

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    Purpose: To examine changes to neuromuscular control of leg stiffness following 42 min of soccer-specific exercise. Methods: Ten youth soccer players, aged 15.8 ± 0.4 years, stature 1.73 ± 0.06 m and mass 59.8 ± 9.7 kg, hopped on a force plate at a self-selected frequency before and after simulated soccer exercise performed on a non-motorised treadmill. During hopping, muscle activity was measured using surface electromyography from four lower limb muscles and analysed to determine feedforward- and feedback-mediated activity, as well as co-contraction. Results: There was a small, non-significant change in stiffness following exercise (26.6 ± 10.6 vs. 24.0 ± 7.0 kN m(-1), p > 0.05, ES = 0.25), with half the group increasing and half decreasing their stiffness. Changes in stiffness were significantly related to changes in centre of mass (CoM) displacement (r = 0.90, p < 0.01, extremely large correlation) but not changes in peak ground reaction force (r = 0.58, p > 0.05, large correlation). A number of significant relationships were observed between changes in stiffness and CoM displacement with changes in feedforward, feedback and eccentric muscle activity of the soleus and vastus lateralis muscles following exercise (r = 0.64-0.98, p < 0.05, large-extremely large correlations), but not with changes in co-contraction (r = 0.11-0.55, p > 0.05, small-large correlations). Conclusions: Following soccer-specific exercise individual changes in feedforward- and reflex-mediated activity of the soleus and vastus lateralis, and not co-contraction around the knee and ankle, modulate changes in CoM displacement and leg stiffness.
  • Article
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    The study aimed to establish the test-retest reliability and convergent validity of PlayerLoad™ (tri-axial accelerometer data) during a standardized bout of treadmill running. Forty-four team-sports players performed two standardized incremental treadmill running tests (7-16 km·h-1) 7 d apart. Players' VO2 (n=20), heart rate (n=44), and tri-axial accelerometer data (PlayerLoad™; n=44) measured at both the scapulae and at the centre of mass (COM), were recorded. Accelerometer data from the individual-component planes of PlayerLoad™ (anterior-posterior PlayerLoad™ [PLAP], medial-lateral PlayerLoad™ [PLML] and vertical PlayerLoad™ [PLV]) were also examined. Moderate to high test-retest reliability was observed for PlayerLoad™ and its individual planes (ICC: 0.80-0.97; CV: 4.2-14.8%) at both unit locations. PlayerLoad™ was significantly higher at COM versus scapulae (223.4 ± 42.6 vs. 185.5 ± 26.3 au; p = 0.001). The percentage contributions of individual planes to PlayerLoad™ were higher for PLML at the COM (scapulae: 20.4 ± 3.8%; COM: 26.5 ± 4.9%; p = 0.001), but lower for PLV (scapulae: 55.7 ± 5.3%; COM: 49.5 ± 6.9%; p = 0.001). Between-subject correlations between PlayerLoad™ and VO2, and between PlayerLoad™ and heart rate, were trivial to moderate (r = -0.43 to 0.33), whereas within-subject correlations were nearly perfect (r = 0.92 to 0.98). PlayerLoad™ had a moderate to high degree of test-retest reliability and demonstrated convergent validity with measures of exercise intensity on an individual basis. However, caution should be applied in making between-athlete contrasts in loading, and when using recordings from the scapulae to identify lower-limb movement patterns.
  • Spreadsheets for analysis of controlled trials, crossovers and time series
    • W G Hopkins
    Hopkins, W. G. (2017a). Spreadsheets for analysis of controlled trials, crossovers and time series. Sportscience 21, 1-4.
  • Article
    Objectives To determine the match-to-match variability in physical activity and technical performance measures in Australian Football, and examine the influence of playing position, time of season, and different seasons on these measures of variability Design Longitudinal observational study. Methods Global positioning system (GPS), accelerometer and technical performance measures (total kicks, handballs, possessions and Champion Data rank) were collected from 33 players competing in the Australian Football League over 31 matches during 2011-2012 (N = 511 observations). The GPS data were categorised into total distance, mean speed (m·min−1), high-speed running (HSR, >14.4 km·h−1), very high-speed running (VHSR, >19.9 km·h−1), and sprint (>23.0 km·h−1) distance whilst player load was collected from the accelerometer. The data was log transformed to provide coefficient of variation (CV) and the between subject standard deviation (expressed as percentages). Results Match-to-match variability was increased for higher speed activities (HSR, VHSR, sprint distance, CV%: 13.3 − 28.6%) compared to global measures (speed, total distance, player load, CV%: 5.3 − 9.2%). The between-match variability was relativity stable for all measures between and within AFL seasons, with only few differences between positions. Higher speed activities (HSR, VHSR, sprint distance), but not mean speed, total distance nor player load, were all higher in the final third phase of the season compared to the start of the season. Conclusions While global measures of physical performance are relatively stable, higher-speed activities and technical measures exhibit a large degree of between-match variability in Australian Football. However, these measures remain relatively stable between positions, and within and between AFL seasons.
  • Article
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    The psychobiological model of endurance performance proposes that perception of effort is the ultimate determinant of endurance performance. Therefore, any physiological or psychological factor affecting perception of effort will affect endurance performance. Accordingly this novel study investigated the effects of a frequently used psychological strategy, motivational self-talk (ST), on rating of perceived exertion (RPE) and endurance performance. In a randomized between groups pre-test - post-test design, 24 participants (mean ± SD age 24.6 ± 7.5 years; V˙O2max 52.3 ± 8.7 ml·kg·min) performed two constant-load (80% peak power output) cycling time to exhaustion tests (TTE), punctuated by a two week ST intervention or a control phase. Group (ST vs. Control) x test (Pre-test vs. Post-test) mixed model ANOVA's revealed that ST significantly enhanced TTE from pre-test to post-test (637 ± 210 s vs. 750 ± 295 s, p < 0.05) with no change in the control group (486 ± 157 s vs. 474 ± 169 s). Moreover, a group x test x iso-time (0%, 50%, 100%) mixed model ANOVA revealed a significant interaction for RPE, with follow-up tests showing that motivational self-talk significantly reduced RPE at 50% iso-time (7.3 ± 0.6 vs. 6.4 ± 0.8, p < 0.05), with no significant difference in the control group (6.9 ± 1.9 vs. 7.0 ± 1.7). This study is the first to demonstrate that ST significantly reduces RPE and enhances endurance performance. The findings support the psychobiological model of endurance performance and illustrate that psychobiological interventions designed to specifically target favorable changes in perception of effort are beneficial to endurance performance. Consequently this psychobiological model offers an important and novel perspective for future research investigations.
  • Article
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    Abstract The aims of this study were to: (1) quantify match running performance in 5-min periods to determine if players fatigue or modulate high-intensity running according to a pacing strategy, and (2) examine factors impacting high-intensity running such as score line, match importance and the introduction of substitutes. All players were analysed using a computerised tracking system. Maintaining 'high' levels of activity in the first half resulted in a 12% reduction (P < 0.01) in the second half for high-intensity running (effect size [ES]: 0.8), while no changes were observed in 'moderate' and 'low' groups (ES: 0.0-0.2). The 'high' group covered less (P < 0.01) high-intensity running in the initial 10-min of the second versus first half (ES: 0.6-0.7), but this was not observed in 'moderate' and 'low' groups (ES: 0.2-0.4). After the most intense periods, players demonstrated an 8% drop in high-intensity running (P < 0.05) compared to the match average (ES: 0.2) and this persisted for 5-min before recovering. Players covered similar high-intensity running distances in matches with differing score lines but position-specific trends indicated central defenders covered 17% less (P < 0.01) and attackers 15% more high-intensity running during matches that were heavily won versus lost (ES: 0.9). High-intensity running distances were comparable in matches of differing importance, but between-half trends indicated that only declines (P < 0.01) occurred in the second half of critical matches (ES: 0.2). Substitutes covered 15% more (P < 0.01) high-intensity running versus the same time period when completing a full match (ES: 0.5). The data demonstrate that high-intensity running in the second half is impacted by the activity of the first half and is reduced for 5-min after intense periods. High-intensity running is also influenced by score line and substitutions but not match importance. More research is warranted to establish if fluctuations in match running performance are primarily a consequence of fatigue, pacing or tactical and situational influences.
  • Article
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    To determine differences in LoadTM·min-1 (au) between standards of Netball match play. Load™·min-1 (au) representing accumulated accelerations measured by tri-axial accelerometers was recorded during matches of two higher and two lower standard teams (n = 32 players). Differences in Load™·min-1 (au) were compared within and between standards for playing position and periods of play. Differences were considered meaningful if there was a > 75 percent likelihood of exceeding a small (0.2) Effect size. Mean (± SD) full match Load™·min-1 (au) for the higher and lower standards were 9.96 ± 2.50 and 6.88 ± 1.88 respectively (100 percent likely lower). The higher standard had greater (mean 97 percent likely) Load™·min-1 (au) values in each position. The difference between first and second half Load™·min-1 (au) was unclear at the higher standard, whilst lower grade centre players had a lower (-7.7 ± 10.8 percent, 81 percent likely) Load™·min-1 (au) in the second half and in all quarters compared to the first. There was little intra-standard variation in individual vector contributions to Load™·min-1 (au), however higher standard players accumulate a greater proportion of the total in the vertical plane (mean 93 percent likely). Higher standard players produce greater Load™·min-1 (au) than their lower standard counterparts in all positions. Playing standard influences the pattern of Load™·min-1 (au) accumulation across a match and individual vector analysis suggests different standard players have dissimilar movement characteristics. Load™·min-1 (au) appears to be a useful method for assessing activity profile in Netball.
  • To describe the external load of Australian football matches and training using accelerometers. Nineteen elite and 21 subelite Australian footballers wore accelerometers during matches and training. Accelerometer data were expressed in 2 ways: from all 3 axes (player load; PL) and from all axes when velocity was below 2 m/s (PLSLOW). Differences were determined between 4 playing positions (midfielders, nomadics, deeps, and ruckmen), 2 playing levels (elite and subelite), and matches and training using percentage change and effect size with 90% confidence intervals. In the elite group, midfielders recorded higher PL than nomadics and deeps did (8.8%, 0.59 ± 0.24; 34.2%, 1.83 ± 0.39 respectively), and ruckmen were higher than deeps (37.2%, 1.27 ± 0.51). Elite midfielders, nomadics, and ruckmen recorded higher PLSLOW than deeps (13.5%, 0.65 ± 0.37; 11.7%, 0.55 ± 0.36; and 19.5%, 0.83 ± 0.50, respectively). Subelite midfielders were higher than nomadics, deeps, and ruckmen (14.0%, 1.08 ± 0.30; 31.7%, 2.61 ± 0.42; and 19.9%, 0.81 ± 0.55, respectively), and nomadics and ruckmen were higher than deeps for PL (20.6%, 1.45 ± 0.38; and 17.4%, 0.57 ± 0.55, respectively). Elite midfielders, nomadics, and ruckmen recorded higher PL (7.8%, 0.59 ± 0.29; 12.9%, 0.89 ± 0.25; and 18.0%, 0.67 ± 0.59, respectively) and PLSLOW (9.4%, 0.52 ± 0.30; 11.3%, 0.68 ± 0.25; and 14.1%, 0.84 ± 0.61, respectively) than subelite players. Small-sided games recorded the highest PL and PLSLOW and were the only training drill to equal or exceed the load from matches across positions and playing levels. PL differed between positions, with midfielders the highest, and between playing levels, with elite higher. Differences between matches and training were also evident, with PL from small-sided games equivalent to or higher than matches.
  • Article
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    Purpose: To determine the impact of neuromuscular fatigue (NMF) assessed from variables obtained during a countermovement jump on exercise intensity measured with triaxial accelerometers (load per minute [LPM]) and the association between LPM and measures of running activity in elite Australian Football. Methods: Seventeen elite Australian Football players performed the Yo-Yo Intermittent Recovery Test level 2 (Yo-Yo IR2) and provided a baseline measure of NMF (flight time:contraction time [FT:CT]) from a countermovement jump before the season. Weekly samples of FT:CT, coaches' rating of performance (votes), LPM, and percent contribution of the 3 vectors from the accelerometers in addition to high-speed-running meters per minute at >15 km/h and total distance relative to playing time (m/min) from matches were collected. Samples were divided into fatigued and nonfatigued groups based on reductions in FT:CT. Percent contributions of vectors to LPM were assessed to determine the likelihood of a meaningful difference between fatigued and nonfatigued groups. Pearson correlations were calculated to determine relationships between accelerometer vectors and running variables, votes, and Yo-Yo IR2 score. Results: Fatigue reduced the contribution of the vertical vector by (mean ± 90% CI) -5.8% ± 6.1% (86% likely) and the number of practically important correlations. Conclusions: NMF affects the contribution of individual vectors to total LPM, with a likely tendency toward more running at low speed and less acceleration. Fatigue appears to limit the influence of the aerobic and anaerobic qualities assessed via the Yo-Yo IR2 test on LPM and seems implicated in pacing.
  • Article
    Objectives: The purpose of this study was to analyse energetic and biomechanical parameters of sprinting on sand surface, aimed at the evaluation of inherent aspects of soccer training programs, injury prevention and recovery processes. Design: Twenty-nine professional soccer players took part in this study: they performed maximal sprints and maximal shuttle sprints on a 12m distance on natural grass, artificial turf and soft, dry sand. Methods: Speed, acceleration, deceleration, stride length, stride frequency, flight and contact time, estimated energy cost, metabolic and mechanical power, efficiency and stiffness values, have been calculated through the instrument SPI-Pro (GPSports, Canberra, Australia) supported by two fixed cameras. Results: The comparison between values recorded on sand with those recorded on natural or artificial grass has highlighted significant decreases (p<0.001) of speed, acceleration, stride length, flight time and mechanical power, efficiency and stiffness. Contact time, energy cost, metabolic power (p<0.001) and deceleration (p<0.05) were higher on sand whereas no significant differences were found regarding stride frequency (p>0.05). Conclusions: These results show that on sand it is possible to perform maximal intensity sprints with higher energy expenditure and metabolic power values, without reaching maximum speed and with smaller impact shocks. Furthermore, exercises with change of direction carried out on this surface allow to reach higher deceleration values. In addition, sprinting on sand potentially entails a limited stretch of the involved muscles. It can therefore offer a valid alternative to traditional training, injury prevention and rehabilitation programs.
  • Article
    Full-text available
    To examine variations in neuromuscular and hormonal status and their relationship to performance throughout a season of elite Australian Rules Football (ARF). Fifteen elite ARF players performed a single jump (CMJ1) and 5 repeated countermovement jumps (CMJ5), and provided saliva samples for the analysis of cortisol (C) and testosterone (T) before the season commenced (Pre) and during the 22-match season. Magnitudes of effects were reported with the effect size (ES) statistic. Correlations were performed to analyze relationships between assessment variables and match time, training load, and performance. CMJ1Flight time:Contraction time was substantially reduced on 60% of measurement occasions. Magnitudes of change compared with Pre ranged from 1.0+/-7.4% (ES 0.04+/-0.29) to -17.1+/-21.8% (ES -0.77+/-0.81). Cortisol was substantially lower (up to -40+/-14.1%, ES of -2.17+/-0.56) than Pre in all but one comparison. Testosterone response was varied, whereas T:C increased substantially on 70% of occasions, with increases to 92.7+/-27.8% (ES 2.03+/-0.76). CMJ1Flight time:Contraction time (r=.24+/-0.13) and C displayed (r=-0.16+/-0.1) small correlations with performance. The response of CMJ1Flight time:Contraction time suggests periods of neuromuscular fatigue. Change in T:C indicates subjects were unlikely to have been in a catabolic state during the season. Increase in C compared with Pre had a small negative correlation with performance. Both CMJ1Flight time:Contraction time and C may be useful variables for monitoring responses to training and competition in elite ARF athletes.
  • Article
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    This study aimed to quantify the influence of neuromuscular fatigue (NMF) via flight time to contraction time ratio (FT:CT) obtained from a countermovement jump on the relationships between yo-yo intermittent recovery (level 2) test (yo-yo IR2), match exercise intensity (HIR m·min and Load™·min) and Australian football (AF) performance.Thirty seven data sets were collected from 17 different players across 22 elite AF matches. Each data set comprised an athlete's yo-yo IR2 score prior to the start of the season, match exercise intensity via Global Positioning System and on-field performance rated by coaches' votes and number of ball disposals. Each data set was categorised as normal (>92% baseline FT:CT, n = 20) or fatigued (<92% baseline FT:CT, n = 17) from a single countermovement jump performed 96 hours after the previous match. Moderation-mediation analysis was completed with yo-yo IR2 (independent variable), match exercise intensity (mediator) and AF performance (dependent variable) with NMF status as the conditional variable. Isolated interactions between variables were analysed by Pearson's correlation and effect size statistics.Yo-yo IR2 score showed an indirect influence on number of ball disposals via HIR m·min regardless of NMF status (normal FT:CT indirect effect = 0.019 p <0.1, reduced FT:CT indirect effect = 0.022 p <0.1). However, yo-yo IR2 score only influenced coaches' votes via Load™·min in the non-fatigued state (normal: FT:CT indirect effect = 0.007 p <0.1, reduced: FT:CT indirect effect = -0.001 p > 0.1). In isolation, NMF status also reduces relationships between yo-yo IR2 and load™·min, yo-yo IR2 and coaches votes, Load™·min and coaches' votes (Δr > 0.1).Routinely testing yo-yo IR2 capacity, NMF via FT:CT and monitoring Load™·min in conjunction with HIR m·min as exercise intensity measures in elite AF is recommended.
  • Article
    Full-text available
    Global positioning system (GPS) technology was made possible after the invention of the atomic clock. The first suggestion that GPS could be used to assess the physical activity of humans followed some 40 y later. There was a rapid uptake of GPS technology, with the literature concentrating on validation studies and the measurement of steady-state movement. The first attempts were made to validate GPS for field sport applications in 2006. While GPS has been validated for applications for team sports, some doubts continue to exist on the appropriateness of GPS for measuring short high-velocity movements. Thus, GPS has been applied extensively in Australian football, cricket, hockey, rugby union and league, and soccer. There is extensive information on the activity profile of athletes from field sports in the literature stemming from GPS, and this includes total distance covered by players and distance in velocity bands. Global positioning systems have also been applied to detect fatigue in matches, identify periods of most intense play, different activity profiles by position, competition level, and sport. More recent research has integrated GPS data with the physical capacity or fitness test score of athletes, game-specific tasks, or tactical or strategic information. The future of GPS analysis will involve further miniaturization of devices, longer battery life, and integration of other inertial sensor data to more effectively quantify the effort of athletes.
  • Article
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    Soccer referees' physical match performances at the start of the second half (46-60 min) were evaluated in relation to both the corresponding phase of the first half (0-15 min) and players' performances during the same match periods. Match analysis data were collected (Prozone, UK) from 12 soccer referees on 152 English Premier League matches during the 2008/09 soccer season. Physical match performance categories for referees and players were total distance, high-speed running distance (speed >5.5 m/s), and sprinting distance (>7.0 m/s). The referees' heart rate was recorded from the start of their warm-up to the end of the match. The referees' average distances (in meters) from the ball and fouls were also calculated. No substantial differences were observed in duration (16:42 ± 2:35 vs 16:27 ± 1:00 min) or intensity (107 ± 11 vs 106 ± 14 beats/ min) of the referees' preparation periods immediately before each half. Physical match performance was reduced during the initial phase of the second half when compared with the first half in both referees (effect sizes-standardized mean differences-0.19 to 0.73) and players (effect sizes 0.20 to 1.01). The degree of the decreased performance was consistent between referees and players for total distance (4.7 m), high-speed running (1.5 m), and sprinting (1.1 m). The referees were closer to the ball (effect size 0.52) during the opening phase the second half. Given the similarity in the referees' preparation periods, it may be that the reduced physical match performances observed in soccer referees during the opening stages of the second half are a consequence of a slower tempo of play.
  • Article
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    The aim of the present study was to verify the validity of using exercise heart rate (HRex), HR recovery (HRR) and post-exercise HR variability (HRV) during and after a submaximal running test to predict changes in physical performance over an entire competitive season in highly trained young soccer players. Sixty-five complete data sets were analyzed comparing two consecutive testing sessions (3–4 months apart) collected on 46 players (age 15.1 ± 1.5 years). Physical performance tests included a 5-min run at 9 km h−1 followed by a seated 5-min recovery period to measure HRex, HRR and HRV, a counter movement jump, acceleration and maximal sprinting speed obtained during a 40-m sprint with 10-m splits, repeated-sprint performance and an incremental running test to estimate maximal cardiorespiratory function (end test velocity V Vam-Eval). Possible changes in physical performance were examined for the players presenting a substantial change in HR measures over two consecutive testing sessions (greater than 3, 13 and 10% for HRex, HRR and HRV, respectively). A decrease in HRex or increase in HRV was associated with likely improvements in V Vam-Eval; opposite changes led to unclear changes in V Vam-Eval. Moderate relationships were also found between individual changes in HRR and sprint [r = 0.39, 90% CL (0.07;0.64)] and repeated-sprint performance [r = −0.38 (−0.05;−0.64)]. To conclude, while monitoring HRex and HRV was effective in tracking improvements in V Vam-Eval, changes in HRR were moderately associated with changes in (repeated-)sprint performance. The present data also question the use of HRex and HRV as systematic markers of physical performance decrements in youth soccer players.
  • Article
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    The aim of this study was to verify if yo-yo intermittent recovery test (level 2) (yo-yo IR2) score is linked to Australian football (AF) performance through match exercise intensity. Six week prospective study design. Twenty-one data sets were recorded from nine individual players that completed the yo-yo IR2, and played an Australian Football League match in the first five rounds of the 2010 season wearing a global positioning system (GPS) unit. Simple mediation modelling was used to analyse the inter-relationship between yo-yo IR2 score, match exercise intensity and AF performance. Playing position and experience were also incorporated into the model to identify conditional affects. A significant direct relationship was observed between yo-yo IR2 and number of ball disposals (p<0.1) and a significant indirect relationship was observed between yo-yo IR2 and number of ball disposals through distance travelled at high intensity (HIR m min(-1)) (p<0.1). Moderation analysis showed that playing position affected the relationship between of yo-yo IR2 and HIR m min(-1) (p<0.1) and HIR m min(-1) and total ball disposals (p<0.1). Playing experience also significantly affected the relationship between HIR m min(-1) and total ball disposals. This study is the first to identify the effects of yo-yo IR2 on total ball disposals through HIR m min(-1) performed during AF matches, and that playing position and playing experience affect these interactions.
  • To assess the validity and reliability of distance data measured by global positioning system (GPS) units sampling at 1 and 5 Hz during movement patterns common to team sports. Twenty elite Australian Football players each wearing two GPS devices (MinimaxX, Catapult, Australia) completed straight line movements (10, 20, 40 m) at various speeds (walk, jog, stride, sprint), changes of direction (COD) courses of two different frequencies (gradual and tight), and a team sport running simulation circuit. Position and speed data were collected by the GPS devices at 1 and 5 Hz. Distance validity was assessed using the standard error of the estimate (±90% confidence intervals [CI]). Reliability was estimated using typical error (TE) ± 90% CI (expressed as coefficient of variation [CV]). Measurement accuracy decreased as speed of locomotion increased in both straight line and the COD courses. Difference between criterion and GPS measured distance ranged from 9.0% to 32.4%. A higher sampling rate improved validity regardless of distance and locomotion in the straight line, COD and simulated running circuit trials. The reliability improved as distance traveled increased but decreased as speed increased. Total distance over the simulated running circuit exhibited the lowest variation (CV 3.6%) while sprinting over 10 m demonstrated the highest (CV 77.2% at 1 Hz). Current GPS systems maybe limited for assessment of short, high speed straight line running and efforts involving change of direction. An increased sample rate improves validity and reliability of GPS devices.
  • Article
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    This study investigated fatigue-induced changes in spring-mass model characteristics during repeated running sprints. Sixteen active subjects performed 12 × 40 m sprints interspersed with 30 s of passive recovery. Vertical and anterior-posterior ground reaction forces were measured at 5-10 m and 30-35 m and used to determine spring-mass model characteristics. Contact (P < 0.001), flight (P < 0.05) and swing times (P < 0.001) together with braking, push-off and total stride durations (P < 0.001) lengthened across repetitions. Stride frequency (P < 0.001) and push-off forces (P < 0.05) decreased with fatigue, whereas stride length (P = 0.06), braking (P = 0.08) and peak vertical forces (P = 0.17) changes approached significance. Center of mass vertical displacement (P < 0.001) but not leg compression (P > 0.05) increased with time. As a result, vertical stiffness decreased (P < 0.001) from the first to the last repetition, whereas leg stiffness changes across sprint trials were not significant (P > 0.05). Changes in vertical stiffness were correlated (r > 0.7; P < 0.001) with changes in stride frequency. When compared to 5-10 m, most of ground reaction force-related parameters were higher (P < 0.05) at 30-35 m, whereas contact time, stride frequency, vertical and leg stiffness were lower (P < 0.05). Vertical stiffness deteriorates when 40 m run-based sprints are repeated, which alters impact parameters. Maintaining faster stride frequencies through retaining higher vertical stiffness is a prerequisite to improve performance during repeated sprinting.
  • Article
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    Time motion analysis is extensively used to assess the demands of team sports. At present there is only limited information on the reliability of measurements using this analysis tool. The aim of this study was to establish the reliability of an individual observer's time motion analysis of rugby union. Ten elite level rugby players were individually tracked in Southern Hemisphere Super 12 matches using a digital video camera. The video footage was subsequently analysed by a single researcher on two occasions one month apart. The test-retest reliability was quantified as the typical error of measurement (TEM) and rated as either good (<5% TEM), moderate (5-10% TEM) or poor (>10% TEM). The total time spent in the individual movements of walking, jogging, striding, sprinting, static exertion and being stationary had moderate to poor reliability (5.8-11.1% TEM). The frequency of individual movements had good to poor reliability (4.3-13.6% TEM), while the mean duration of individual movements had moderate reliability (7.1-9.3% TEM). For the individual observer in the present investigation, time motion analysis was shown to be moderately reliable as an evaluation tool for examining the movement patterns of players in competitive rugby. These reliability values should be considered when assessing the movement patterns of rugby players within competition.
  • Article
    Measurements of exercise heart rate (HR(ex)), HR recovery (HRR) and HR variability (HRV) are used as indices of training status. However, the day-to-day variability of these indices throughout a competitive soccer period is unknown. On 14 occasions during a 3-week competition camp, 18 under 15 (U15) and 15 under 17 (U17) years soccer players performed a 5-min submaximal run, followed by a seated 5-min recovery period. HR(ex) was determined during the last 30 s of exercise, while HRR and HRV were measured during the first and last 3 min of the post-exercise recovery period, respectively. U15 players displayed greater HR(ex) (P = 0.02) and HRR (P = 0.004) compared with the U17 players, but there was no difference in HRV (P = 0.74). The mean coefficient of variation (CV) for HR(ex) was lower than that for HRV [3.4 (90% CL, 3.1, 3.7) vs. 10.7 (9.6, 11.9)%, P < 0.001]; both were lower than that for HRR [13.3 (12.2, 14.3)%, P < 0.01]. In contrast to HR(ex) and HRR, the CV for HRV was correlated to maximal aerobic speed (r = -0.52, P = 0.002). There was no correlation between total activity time (training sessions + matches) and CV of any of the quantified variables. The variability of each of these measures and player fitness levels should be considered when interpreting changes in training status.
  • Article
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    Small-skied games (SSGs) are frequently used as an alternative to interval training to provide an aerobic training stimulus.' Although the variability of the physical, perceptual, and physiological responses during SSGs training has been previously established,(2,3) an understanding of the reproducibility of the acute physiological responses and movement demands of these games, when completed within the same session and between different training sessions, is also important. This information may allow coaches to better control the SSG training process with soccer players. Consequently, the aim of this study was to determine the within- and between-training session reproducibility of two SSG formats (2 versus 2 and 4 versus 4 players) and two regimes (intermittent and continuous).
  • To examine the acute and short-term responses of variables obtained during a single countermovement jump (CMJ1); repeated countermovement jump involving 5 consecutive efforts without a pause (CMJ5); and cortisol, testosterone, and testosterone-to-cortisol ratio (T:C) to an elite Australian Rules Football (ARF) match with a view to determining which variables may be most useful for ongoing monitoring. Twenty-two elite ARF players participating in a preseason cup match performed a CMJ1 and a CMJ5 and provided saliva samples 48 h before the match (48pre), prematch (Pre), postmatch, 24 h post (24post), 72 h post (72post), 96 h post (96post), and 120 h post (120post). The magnitude of change in variables at each time point compared with Pre and 48pre was analyzed using the effect size (ES) statistic. A substantial decrement in the pre- to postmatch comparison occurred in the ratio of CMJ1 Flight time:Contraction time (ES -0.65 +/- 0.28). Cortisol (ES 2.34 +/- 1.06) and T:C (ES -0.52 +/- 0.42) displayed large pre- to postmatch changes. The response of countermovement variables at 24post and beyond compared with prematch and 48pre was varied, with only CMJ1 Flight time:Contraction time displaying a substantial decrease (ES -0.32 +/- 0.26) postmatch compared with 48pre. Cortisol displayed a clear pattern of response with substantial elevations up to 24post compared with Pre and 48pre. CMJ1 Flight time:Contraction time appears to be the most useful variable for monitoring neuromuscular status in elite ARF players due to its substantial change compared with 48pre and prematch. Monitoring cortisol, due to its predictable pattern of response, may provide a useful measure of hormonal status.
  • Article
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    To establish the reliability of various measures obtained during single and repeated countermovement jump (CMJ) performance in an elite athlete population. Two studies, each involving 15 elite Australian Rules Football (ARF) players were conducted where subjects performed two days, separated by one week, of AM and PM trials of either a single (CMJ1) or 5 repeated CMJ (CMJ5). Each trial was conducted on a portable force-plate. The intraday, interday, and overall typical error (TE) and coefficient of variation (CV%) were calculated for numerous variables in each jump type. A number of CMJ1 and CMJ5 variables displayed high intraday, interday, and overall reliability. In the CMJ1 condition, mean force (CV 1.08%) was the most reliable variable. In the CMJ5, flight time and relative mean force displayed the highest repeatability with CV of 1.88% and 1.57% respectively. CMJ1Mean force was the only variable with an overall TE < smallest worthwhile change (SWC). Selected variables obtained during CMJ1 and CMJ5 performance can be used to assess the impact of both acute and chronic training and competition. Variables derived from the CMJ5 may respond differently than their CMJ1 counterparts and should provide insights into differential mechanisms of response and adaptation.
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    To determine the movement patterns and physiological demands of top-class soccer assistant referees, we performed computerized time-motion analysis and measured heart rate and blood lactate concentration in 15 assistant referees during 22 competitive matches in the top Danish league. To relate match performance to the physical capability of the assistant referees, they performed a 3 x 30 m sprint protocol before and after matches and a laboratory treadmill test within 3 weeks of the games. The mean total distance covered by the top-class assistant referees was 7.28 (range 5.78-8.16) km, of which 1.15 (0.86-1.44) km was high-intensity running and 1.16 (0.12-2.34) km was sideways running. The amount of high-intensity running during a game was correlated with performance of repeated sprints (r = 0.80, P < 0.05). Mean heart rate was 137 (117-159) beats x min(-1), corresponding to 73% (60-88%) of maximal heart rate and 65% (53-80%) of maximal oxygen uptake. Blood lactate concentration was 4.7 (1.6-11.0) and 4.8 (1.1-13.7) mmol x 1(-1) after the first and second half, respectively. Sprinting performance was poorer (P < 0.05) after than before the games. The peak distance to the offside line was greater (P < 0.05) in the second than the first half (7 +/- 1 vs 5 +/- 0 m). Our results show that: (1) top-class assistant soccer refereeing is characterized by brief intense bouts of forward and sideways running interspersed with long periods of low activity; (2) top-class soccer assistant referees have moderate aerobic energy production during games with episodes of high aerobic and anaerobic energy turnover; (3) assistant referees' performance of repeated sprints correlates with the amount of high-intensity running performed in a game; and (4) sprint performance decreases towards the end of a game, which appears to affect assistant referees' ability to keep up with play.
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    Repeated supramaximal exercise training is an efficient means of improving both aerobic and anaerobic energy system capacities. However, the influence of different levels of supramaximal training on parasympathetic function is unknown. To compare the effects of repeated-sprint (RS) versus high-intensity intermittent training (HIT) on performance and postexercise parasympathetic reactivation in trained adolescents. Fifteen male adolescents (15.6 +/- 0.8 yr) were divided into two groups that performed 9 wk of either RS (repeated all-out 6-s shuttle sprints; 14-20 s of recovery; N = 8) or HIT (15- to 20-s runs at 95% of the speed reached at the end of the 30-15 intermittent fitness test (V(IFT)); 15-20 s of recovery; N = 7). Groups performed intervals twice per week and maintained similar external training programs. Before and after training, performance was assessed by the V(IFT), countermovement jump (CMJ), 10-m sprint time (10 m), mean RS ability time (RSAmean), and heart rate (HRsub) level during a 6-min submaximal (60% V(IFT)) exercise test, where parasympathetic reactivation was assessed during the recovery phase (i.e., HR recovery time constant (HRRtau) and HR variability (HRV)). Parasympathetic function, V(IFT), and RSAmean were improved with HIT but not RS training. In contrast, changes in CMJ and HRsub were similar in both groups. A significant relationship was shown between the decrease in HRRtau and RSAmean (r = 0.62, P < 0.05; N = 15). HIT was more effective than RS training at improving postexercise parasympathetic function and physical performance. In addition, HRRtau, which was more sensitive to training than HRV indices, seems to be a useful performance-related measurement.
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    To investigate the time course of recovery from neuromuscular fatigue and some biochemical changes between two female soccer matches separated by an active or passive recovery regime. Countermovement jump (CMJ), sprint performance, maximal isokinetic knee flexion and extension, creatine kinase (CK), urea, uric acid, and perceived muscle soreness were measured in 17 elite female soccer players before, immediately after, 5, 21, 45, 51, and 69 h after a first match, and immediately after a second match. Eight players performed active recovery (submaximal cycling at 60% of HRpeak and low-intensity resistance training at < 50% 1RM) 22 and 46 h after the first match. In response to the first match, a significant decrease in sprint performance (-3.0 +/- 0.5%), CMJ (-4.4 +/- 0.8%), peak torque in knee extension (-7.1 +/- 1.9%) and flexion (-9.4 +/- 1.8%), and an increase in CK (+ 152 +/- 28%), urea (15 +/- 2), uric acid (+ 11 +/- 2%), and muscle soreness occurred. Sprint ability was first to return to baseline (5 h) followed by urea and uric acid (21 h), isokinetic knee extension (27 h) and flexion (51 h), CK, and muscle soreness (69 h), whereas CMJ was still reduced at the beginning of the second match. There were no significant differences in the recovery pattern between the active and passive recovery groups. The magnitude of the neuromuscular and biochemical changes after the second match was similar to that observed after the first match. The present study reveals differences in the recovery pattern of the various neuromuscular and biochemical parameters in response to a female soccer match. The active recovery had no effects on the recovery pattern of the four neuromuscular and three biochemical parameters.