Matthew Weston

Motion analysis of match-play in elite U12 to U16 age-group soccer players

Abstract The aim of this study was to quantify the motion demands of match-play in elite U12 to U16 age-group soccer players. Altogether, 112 players from two professional soccer clubs at five age-group levels (U12–U16) were monitored during competitive matches (n = 14) using a 5 Hz non-differential global positioning system (NdGPS). Velocity thresholds were normalized for each age-group using the mean squad times for a flying 10 m sprint test as a reference point. Match performance was reported as total distance, high-intensity distance, very high-intensity distance, and sprint distance. Data were reported both in absolute (m) and relative (m · min−1) terms due to a rolling substitute policy. The U15 (1.35 ± 0.09 s) and U16 (1.31 ± 0.06 s) players were significantly quicker than the U12 (1.58 ± 0.10 s), U13 (1.52 ± 0.07 s), and U14 (1.51 ± 0.08 s) players in the flying 10 m sprint test (P < 0.001). The U16 age-group covered significantly more absolute total distance (U16 > U12, U13, U14), high-intensity distance (U16 > U12, U13, U14, U15), very high-intensity distance (U16 > U12, U13), and sprint distance (U16 > U12, U13) than their younger counterparts (P < 0.05). When the data are considered relative to match exposure, few differences are apparent. Training prescription for youth soccer players should consider the specific demands of competitive match-play in each age-group.

The Impact of Specific High-Intensity Training Sessions on Football Referees’ Fitness Levels:

Background In comparison to the amount of literature that has examined the match demands of football refereeing, there has been little attempt to assess the impact of high-intensity training. Purpose The main goals were to get a better understanding of the long-term effect of specific intermittent training. Study Design The authors examined the cardiovascular strain of specific high-intensity training sessions and also their impact on referees’ fitness levels. Methods To examine the physical workload during intensive intermittent training sessions, heart rates were recorded and analyzed relative to the referees’ maximum heart rate (HRmax). To assess the referees’ fitness levels, the Yo-Yo intermittent recovery test was used. Results Both the pitch- and track-training sessions were successful in imposing an appropriate high intensity load on the referees, at 86.4 ± 2.9% and 88.2 ± 2.4% HRmax, respectively. Following 16 months of intermittent high-intensity training, referees improved their performance on the Yo-Yo intermittent recovery test by 46.5%, to a level that is comparable with professional players. Conclusions As match officials are subjected to a high physical load during matches, they should follow structured weekly training plans that have an emphasis on intensive, intermittent training sessions.

Errors in judging “offside” in association football: Test of the optical error versus the perceptual flash-lag hypothesis

Abstract The objective of this study was to analyse the correctness of the offside judgements of the assistant referees during the final round of the FIFA 2002 World Cup. We also contrasted two hypotheses to explain the errors in judging offside. The optical error hypothesis is based on an incorrect viewing angle, while the flash-lag hypothesis refers to perceptual errors associated with the flash-lag effect (i.e. a moving object is perceived as spatially leading its real position at a discrete instant signalled by a briefly flashed stimulus). Across all 64 matches, 337 offsides were analysed using digital video technology. The error percentage was 26.2%. During the first 15 min match period, there were significantly more errors (38.5%) than during any other 15 min interval. As predicted by the flash-lag effect, we observed many more flag errors (86.6%) than non-flag errors (13.4%). Unlike the predictions of the optical error hypothesis, there was no significant difference between the correct and incorrect decisions in terms of the positioning of the assistant referees relative to the offside line (0.81 and 0.77 m ahead, respectively). To reduce the typical errors in judging offside, alternative ways need to be considered to teach assistant referees to better deal with flash-lag effects.

Science and medicine applied to soccer refereeing: An Update

Soccer referees are required to keep up with play at all times to ensure optimal positioning in making key decisions. While the physiological aspects of soccer refereeing have been extensively reviewed, other key areas of preparation and performance have yet to be considered in detail. We present a contemporary examination of methodological considerations for the interpretation of referees’ match activities, the validation of fitness testing and training protocols, match and training injury profiles, and the understanding and development of perceptual-cognitive expertise.A referee covers approximately 11 km during a match, with ~900 m of high-speed running and, consequently, the demands of match play represent a significant physical challenge. The analyses of within-match activity profiles have attempted to assess the possible occurrence of referee fatigue, with equivocal findings. However, researchers have demonstrated that referees’ physical performances are interrelated with those of the players during the same match. Therefore, the evaluation of referees’ match activity profiles should be made in the context of the players’ performances. High match-to-match variability in key variables, namely, high-speed running and sprinting, along with age-related reductions in match running are other factors that require due consideration when interpreting physical performances. Fitness testing is used by national and international referee governing bodies as part of their match selection criteria. Therefore, the tests need to reflect the physical task of refereeing, yet for the recent fitness tests introduced by the Fédération Internationale de Football Association — a 20×150m high-intensity and 6×40m repeated-sprint test — only the repeated-sprint test possesses the appropriate construct validity for assessment of match-related running capacity. Also, the performance standards of the tests have not been validated. Consequently, the scientific rationale behind the tests and their associated standards is not clear. Soccer referees dedicate a large proportion of their overall training to the development of physical capacity and researchers have demonstrated that high-intensity (>85% maximal heart rate) training protocols are effective for improving fitness and match running performance. These high training loads combined with increasing age could, in part, explain an incidence of non-contact match injuries (18 injuries per 1000 match hours) similar to players, with lower leg muscle strains being the most common type of non-contact injuries in referees. The implementation of injury prevention programmes along with the careful monitoring of training and match loads may help minimize referee’s injury incidence.The perceptual-cognitive demands of soccer refereeing are significant, yet there remains limited research examining the perceptual and cognitive processes informing referees’ decisions. As such, a three-step approach for the study of expertise in soccer referees is proposed. First, objective and reliable markers of decision making should be established, with due consideration to the development of naturalistic test situations while maintaining experimental control. Second, process-tracing measures can be used to identify the perceptual and cognitive mechanisms involved in accurate decision making. Finally, research is required to help understand the acquisition of superior decision making and whether such expertise can be developed via training programmes.

Age-related effects on fitness performance in elite-level soccer referees

Elite soccer referees usually achieve the peak of their officiating careers at an average age that is considerably older than that observed in competitive matched soccer players. As ageing has been reported to negatively affect physical performance, the aim of this study was to investigate the effect of ageing on fitness performance in elite-level soccer referees. Thirty-six elite-level soccer referees were grouped into young (Y, n = 12), average (A, n = 14), and old (O, n = 10) groups, according to their age and observed for field test performance (countermovement jump [CMJ], 50-m and 200-m sprints, and 12-minute running for distance). Results showed a significant age effect on CMJ (r = 20.52, p < 0.001), 200 m (r = 0.51, p < 0.001), and 12-minute time trial running (r = 20.52, p < 0.001). Y jumped higher than A and O groups (p < 0.05) and were faster than O over 200 m (p < 0.05). No group effect was observed for 12-minute run and 50-m performance (p > 0.05), respectively. Sixteen of the 36 referees were further examined for selected physiological variables and grouped into 2 equal (n = 8) age groups (young and old, Y1 and O1, respectively). VO2max was higher in Y1 (p < 0.05), but O1 attained performances similar to Y1 running at selected blood lactate speeds (4 mmol L-1, p > 0.05). Although older referees demonstrated acceptable fitness levels, younger officials should ensure that they develop appropriate levels of aerobic and anaerobic fitness to be able to match the demands placed upon them while refereeing throughout their careers. To promote this, fitness test standards should be age related.

Relationships among field-test measures and physical match performance in elite-standard soccer referees.

Abstract The aim of this study was to assess the extent to which measures derived from the new FIFA referees’ fitness tests can be used to monitor a referees match-related physical capacity. Match-analysis data were collected (Prozone®, Leeds, UK) from 17 soccer referees for 5.0 (s = 1.7) FA Premier League matches per referee during the first 4 months of the 2007–08 season. Physical match performance categories included total distance covered, high-intensity running distance (speed >5.5 m · s−1), and sprinting distance (>7.0 m · s−1). The two tests were a 6 × 40-m sprint test and a 150-m interval test. Heart rate demand was correlated with total match distance covered (r = −0.70, P = 0.002) and high-intensity running (r = −0.57, P = 0.018) in the interval test. The fastest 40-m sprint was related to total distance covered (r = −0.69, P = 0.002), high-intensity running (r = −0.76, P < 0.001), and sprinting distance (r = −0.75, P = 0.001), while mean time for the 40-m sprints was related to total distance covered (r = −0.70, P = 0.002), high-intensity running (r = −0.77, P < 0.001), and sprinting distance (r = −0.77, P < 0.001). The referees who recorded the best interval-test heart rate demand and fastest 40-m time produced the best physical match performances. However, only the sprint test and in particular the fastest 40-m time had appropriate construct validity for the physical assessment of soccer referees.

Evaluating Intervention Fidelity: An Example from a High-Intensity Interval Training Study

Aim Intervention fidelity refers to the degree to which an experimental manipulation has been implemented as intended, but simple, robust methods for quantifying fidelity have not been well documented. Therefore, we aim to illustrate a rigorous quantitative evaluation of intervention fidelity, using data collected during a high-intensity interval training intervention. Design Single-group measurement study. Methods Seventeen adolescents (mean age ± standard deviation [SD] 14.0 ± 0.3 years) attended a 10-week high-intensity interval training intervention, comprising two exercise sessions per week. Sessions consisted of 4-7 45-s maximal effort repetitions, interspersed with 90-s rest. We collected heart rate data at 5-s intervals and recorded the peak heart rate for each repetition. The high-intensity exercise criterion was ≥90% of individual maximal heart rate. For each participant, we calculated the proportion of total exercise repetitions exceeding this threshold. A linear mixed model was applied to properly separate the variability in peak heart rate between- and within-subjects. Results are presented both as intention to treat (including missed sessions) and per protocol (only participants with 100% attendance; n=8). Results For intention to treat, the median (interquartile range) proportion of repetitions meeting the high-intensity criterion was 58% (42% to 68%). The mean peak heart rate was 85% of maximal, with a between-subject SD of 7.8 (95% confidence interval 5.4 to 11.3) percentage points and a within-subject SD of 15.1 (14.6 to 15.6) percentage points. For the per protocol analysis, the median proportion of high-intensity repetitions was 68% (47% to 86%). The mean peak heart rate was 91% of maximal, with between- and within-subject SDs of 3.1 (-1.3 to 4.6) and 3.4 (3.2 to 3.6) percentage points, respectively. Conclusions Synthesising information on exercise session attendance and compliance (exercise intensity) quantifies the intervention dose and informs evaluations of treatment fidelity.

The application of differential ratings of perceived exertion to Australian Football League matches

OBJECTIVES To investigate the application of differential ratings of perceived exertion for the examination of internal load during Australian Football League (AFL) matches. DESIGN Single cohort, observational study. METHODS Using the centiMax rating of perceived exertion (RPE) scale, 26 professional AFL players provided ratings for match exertion (RPE-M), along with differential ratings for breathlessness (RPE-B), leg exertion (RPE-L), and technical demand (RPE-T) following 129 matches (5.0 ± 1.6 matches per player). Global positioning satellite (GPS) and accelerometer measures were also collected. Data were analysed using magnitude-based inferences. RESULTS RPE scores were 93.0 ± 8.2 AU (RPE-M), 89.0 ± 11.0 AU (RPE-B), 91.5 ± 9.8 AU (RPE-L), and 87.0 ± 10.0 AU (RPE-T). There was a most likely small difference between RPE-L and RPE-T (5.5%; ± 90% confidence limits 1.9%), a likely small difference between RPE-L and RPE-B (3.5%; ± 1.5%) and a possibly small difference between RPE-B and RPE-T (1.9%; ± 1.9%). Within-player correlations between RPE and GPS measures were small for RPE-M (r = 0.14-0.28), unclear to small for RPE-B (r = 0.06-0.24) and unclear to moderate for RPE-L (r = 0.06-0.37). Differential RPEs combined to explain 76% of the variance in RPE-M. For all RPE scores, within-player variability was moderate to high (typical error: 7.9-12.4%), and the thresholds for a likely between-match change were 8.8-13.7%. CONCLUSIONS As differential RPEs represent distinct sensory inputs, the collection of these scores facilitate the interpretation of internal match loads and therefore represent a valuable addition to match data collection procedures. Moderate to high within-player variability should be considered when interpreting between-match changes in all RPE scores.

Re-examination of the post half-time reduction in soccer work-rate

OBJECTIVES To re-examine the work-rate of soccer players immediately after a passive half-time interval with an alternative approach to data reduction and statistical contrasts. DESIGN Time-motion analysis data (5Hz global positioning system), were collected from 20 elite youth players (age: 17±1 years) during 21 competitive league fixtures (5±3 matches per player). METHODS Physical performances were categorised into total distance covered, total low-speed running (0-14.9kmh(-1)) and total high-speed running (15.0-35.0kmh(-1)). These dependent variables were subsequently time averaged into pre-determined periods of 5-, 15- and 45-min duration, and expressed in relative (mmin(-1)) terms to allow direct comparisons between match periods of different lengths. During the 15-min half-time interval players were passive (seated rest). RESULTS There was a large reduction in relative total distance covered (effect size - standardised mean difference - 1.85), low-speed running (effect size -1.74) and high-speed running (effect size -1.37) during the opening 5-min phase of the second half (46-50min) when compared to the first half mean (0-45min). When comparing the 51-55 and 56-60-min periods, effect sizes were trivial for relative total distance covered (effect size -0.13; -0.04), low-speed running (effect size -0.10; -0.11) and small/trivial for high-speed running (-0.39; 0.11). CONCLUSIONS Using a more robust analytical approach, the findings of this study support and extend previous research demonstrating that players work-rate was markedly lower in the first 5-min after a passive half-time interval, although we observed this phenomenon to be transient in nature. Time-motion analysts might re-consider their data reduction methods and comparators to distinguish within-match player work-rate trends.

The Interchangeability of Global Positioning System and Semiautomated Video-Based Performance Data During Elite Soccer Match Play

Harley, JA, Lovell, RJ, Barnes, CA, Portas, MD, and Weston, M. The interchangeability of GPS and semiautomated video-based performance data during elite soccer match play. J Strength Cond Res 25(8): 2334-2336, 2011—In elite-level soccer, player motion characteristics are commonly generated from match play and training situations using semiautomated video analysis systems and global positioning system (GPS) technology, respectively. Before such data are used collectively to quantify global player load, it is necessary to understand both the level of agreement and direction of bias between the systems so that specific interventions can be made based on the reported results. The aim of this report was to compare data derived from both systems for physical match performances. Six elite-level soccer players were analyzed during a competitive match using semiautomated video analysis (ProZone® [PZ]) and GPS (MinimaxX) simultaneously. Total distances (TDs), high speed running (HSR), very high speed running (VHSR), sprinting distance (SPR), and high-intensity running distance (HIR; >4.0 m·s-1) were reported in 15-minute match periods. The GPS reported higher values than PZ did for TD (GPS: 1,755.4 ± 245.4 m; PZ: 1,631.3 ± 239.5 m; p < 0.05); PZ reported higher values for SPR and HIR than GPS did (SPR: PZ, 34.1 ± 24.0 m; GPS: 20.3 ± 15.8 m; HIR: PZ, 368.1 ± 129.8 m; GPS: 317.0 ± 92.5 m; p < 0.05). Caution should be exercised when using match-load (PZ) and training-load (GPS) data interchangeably.