Changes in physical performance variables in an English ...

International Journal of Performance Analysis in Sport 2014, 14, 493-503. 45-344.

Changes in physical performance variables in an English Championship League team across the competitive season: the effect of possession Ryland Morgans1, David Adams2, Richard Mullen2, and Morgan D Williams2 1

Liverpool Football Club, Anfield, Liverpool, England, UK. L4 0TH.

2

University of South Wales, Division of Sport, Health and Exercise, Upper Glyntaff, Pontypridd, Wales, UK. CF37 4AT.

Abstract This study examined changes in physical match performance of six players from an English Championship League team across the competitive season and examined the effect of team possession. Sprint and high intensity distances and frequency of efforts were all greatest in earlyseason, and were significantly reduced in both mid-and-late-season phases (all p < 0.0001). None of these variables were, however, related to team possession (p range = 0.2759 to 0.7411). Total distance covered on the other hand was sustained and did not significantly change over the season phases (p = 0.9219), but it was negatively associated with possession (p = 0.0080). This association suggests that physical demands were lower when this team was in possession of the ball. In summary, evidence of residual fatigue at mid-and-late-season was obtained from sprint and high intensity variables. Given possession was associated with a reduced total distance covered during matches, it may be speculated that better quality teams are able to maintain possession for longer periods of matches and thus require less recovery time due to reduced physical match demands. Keywords: Soccer, time-motion analysis, sprinting, high intensity running, possession

1. Introduction The physical demands on soccer players during matches are often assessed using total distance covered and the extent to which that distance is covered at given intensities. Professional players can cover 10-13km in total distance with 8-10% being at high intensity (Mohr et al., 2003; Di Salvo et al., 2009; Di Mascio and Bradley, 2012). Professional players also generally cover greater distances at high intensity than their lower standard counterparts (Bangsbo et al., 1991; Mohr et al., 2003; Andersson et al., 2008; Mohr et al., 2008). Some regard these high intensity distances as a key indicator of physical fitness (Mohr et al., 2003). Yet, players’ current fitness status alone cannot explain the observed total distance and the distances covered at various intensities 493

during matches and other factors have a significant impact (Bangsbo, 1994). For example, Bradley et al. (2009) found that high intensity distances in the English Premier League (EPL) were partly explained by technical differences (pass frequency and accuracy) and tactical (possession or direct style) strategies. In terms of total distance, Rienzi et al. (2000) reported that when a single match was analysed, South American professional players covered 1000m less than EPL players, which they attributed to the tactical restrictions associated with a different style of play. These and other studies suggest that physical and technical actions during match play interact in a dynamic nature (McGarry and Franks, 2003; Reed and O’Donoghue, 2005; Dellal et al., 2011). Exploring the impact of other variables upon total and high intensity distance, as indicators of physical performance would appear to be important for future investigation. Gaining and maintaining ball possession is one variable that might have an impact upon physical match performance variables. Ball possession, described as the ability to pass the ball accurately with minimum touches, and retain the ball when under pressure from the opposition (Lago and Martin, 2007; Redwood-Brown, 2008), has been regarded as a critical factor during matches and allows a team to control the structure and tempo of the match (Shafizadeh et al., 2012). The ability to accurately and successfully pass the ball over a range of distances and in different directions has also been shown to separate elite players from less able counterparts (Lago and Martin, 2007; Redwood-Brown, 2008). Previous research on possession has mainly focused on its determinants (Lago and Martin, 2007), and few studies have reported the effect of possession on physical match performance variables (Bradley et al., 2013a; Morgans et al, In Press). A possession-based style of play may reduce physical demands imposed on players and help preserve performance across the season (Morgans et al, In Press). Bradley et al. (2013a) suggest that when in possession of the ball, a team’s physical demands are lower compared to when they are defending and having to react to opposition movements. If true, the amount of ball possession may determine physical match performance measures. Thus, when teams maintain high possession, they may reduce exposure to high physical demands, which may permit a more sustained physical performance across the season (Morgans et al, In Press). The importance of sustaining match performance across the season to meet the technical, tactical and physical demands of competitive match play has previously been identified as vital for success in domestic league competitions (Collet, 2012). In particular, the demands of the English Championship League (ECL) are high, requiring players to regularly compete with at times, only two days to recover before the next match (Morgans et al, In Press). A likely consequence of such demands and in-adequate recovery is residual fatigue (Cormack et al., 2008), which can result in physical and technical match performance decrements. Moreover, as the season advances the accumulating effect of residual fatigue may further impact match performance in late-season, ultimately impairing match outcome and possibly reducing the chances of promotion to the EPL. To date, despite the impact that physical performance might have on overall team performance during competition, limited research (Morgans et al, In Press) has examined within season changes in physical match performance variables in relation to ball possession. Therefore, the aims of this study were, firstly, to examine the total

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distance, sprint and high intensity distances covered and frequency of efforts of a professional soccer team across an ECL competitive season; and, secondly, to examine the effect of possession on physical match performance.

2. Methods 2.1. Participants Six male participants (mean age = 23.5 ±2.1 years; stature = 1.80 ±0.10 m), representing the core-playing group from an ECL soccer club were monitored across a season. All participants were outfield players (central defenders n = 2, wide defender n = 1, central midfielders n = 3) who made a median of 37 match appearances (min = 27, max = 45), inclusive of domestic cup competitions (maximum number of matches = 49). The average: matches played; time on pitch; time between matches; and matches per day ratio by competition phase are shown in Table 1 for the group. The forward players’ data were excluded due to in-sufficient match appearances made over the season to meet the inclusion criteria. Out of the 49 competitive matches played, 23 were home matches, 23 were away fixtures and the remaining three matches were domestic cup competitions. Only data obtained from home ECL matches were included in the study. This removed the impact of confounding variables such as: different strategies adopted by teams when playing away from home; pitch dimensions; venue; accommodation and travel that have been purported to affect physical demands of matches (Andersson et al., 2007; Lago, 2009; Bradley et al., 2011; Lago-Peñas and Ballesteros, 2011). In total, 95 rows of data formed the dataset used in the analysis with the participants playing a mean of 18 (min = 9, max = 21) home matches. The competition phase was divided into three phases (early = August to November; mid = December to February; and late = March to May). The opponents were determined by the Football League fixture schedule and the quality of opposition (based on league position) was evenly distributed across the season (See Table 2). During the early, mid and late phase of the season the points per match record was 1, 0.9 and 2.2 respectively. The University Human Research Ethics Committee and the professional soccer club from which the participants volunteered approved the study. Table 1. Number of all League and domestic cup matches played, time on pitch, time (hours) between matches and matches per day ratio by competition phase.

Number of matches played Time on pitch (sum) Time on pitch Time between matches (hours) Match:day ratio

Early Mean ±SD

Mid Mean ±SD

Late Mean ±SD

18 ± 5

16 ± 1

9±2

1601 ± 484

1404 ± 175

724 ± 158

89 ± 9

90 ± 6

83 ± 15

171 ± 79

139 ± 7

161 ± 28

7±3

6 ± 0.4

6±1

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Table 2. Distribution of home match opponents’ league position by competition phase. Phase Early

Mid

Late

Match Number 1 3 5 7 10 12 13 16 18 20 22 23 25 28 29 31 34 36 37 40 42 44 46

League Position (LP) 4 13 5 24 15 9 7 2 22 20 3 16 14 21 12 11 18 6 8 1 10 17 23

LP Median

LP Range

11

2 to 24

14

3 to 21

9

1to 23

2.2 Match analysis procedures Using a multi-camera computerised tracking system all outfield players’ movements were captured during each match by eight colour cameras positioned at stadium roof height (Randers et al., 2010) with a sampling frequency of 25Hz. Several authors have previously documented the installation process (e.g., Carling et al., 2008; Randers et al., 2010). Captured data were analysed using match-analysis software (Prozone® Stadium Manager, ProZone® Sports Ltd, Leeds, UK) to produce a single dataset on each player’s activity during a match. The system has been independently validated to verify the capture process and accuracy of data (Carling et al., 2008). Match data for each player during each match were recorded and analysed via the same computerised semi-automatic match analysis system (ProZone®, Stadium Manager Leeds, UK). The set of physical match performance and ball possession variables included: total distance covered; sprint distance (total distance covered >7 m/s); high intensity distance (total distance covered >5.5-6.9 m/s plus sprint distance); frequency of sprint efforts (total number of sprint efforts >7 m/s); and frequency of high intensity efforts (total number of high intensity efforts >5.5-6.9 m/s); possession (time the home team had the ball divided by the time the ball was in play); and time on pitch were reported. The speeds for each category have been previously reported (Di Salvo et al., 2009) and all ProZone® match-analysis has been shown to provide valid and reliable

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measures during competitive match play (e.g., Di Salvo et al., 2006; Carling et al., 2008). 2.3 Statistical analyses All statistical analyses were performed using JMP version 10.02 discovery software (SAS Institute, JMP Statistical Discovery, NC, USA). To assess differences in possession across the phase of season; one-way analysis of variance was used. To examine differences across the season a repeated measures design mixed model using Restricted Maximum Likelihood (REML) method for fitting (fixed factors = competition phase [early, mid and late], and possession; random factor = participant) was used. Possession was included as a fixed factor to control for its purported affect on physical performance. When F statistics for the competition phase were significant, ttests with Bonferroni correction (p < 0.0167) were used. All least square means differences were reported alongside 95% confidence intervals (95% CI). When appropriate, effect size (ES) was also calculated as the mean difference between paired groups divided by the common standard deviation.

3. Results 3.1. Match Performance The descriptive statistics for physical match performance and ball possession across the three competition phases are shown in Table 3. Total distance was the only physical performance variable not to change across the season. All sprint and high intensity physical match performance variables significantly changed across the season. Post-hoc analysis revealed that the same pattern across the season occurred for sprint and high intensity variables (See Table 4). The highest sprint and high intensity distance and frequency of efforts were all found in early-season, followed by a significant decrease at mid-season that remained until late-season. Team possession did not significantly change across the season, although a trend toward significance was observed (p = 0.0804). Yet, on inspection of the ES for the phase of season comparisons of team possession, a level of instability across the season was revealed (early versus mid d = 0.4; early versus late d = 0.8 and mid versus late d = 1.1). Furthermore, when compared to the other physical performance variables, total distance was the only variable with a significant effect (p = 0.0080) for ball possession. From the parameter estimate, when ball possession increased by 1%, total distance covered reduced by 29 m (95% CI 8 to 50 m).

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Table 3: Physical match performance and possession descriptive statistics (mean ± standard deviation) by competition phase.

N

Possession (%)

Total Distance (m)

Sprint Distance (m)

Sprint Frequency

High Intensity Distance (m)

High Intensity Frequency

Early

42

50±6

10513±1196

268±118

37±14

916±299

117±35

Mid

31

48±4

10722±942

183±112

25±13

751±283

93±28

Late

22

53±3

10556±1044

192±93

26±11

811±280

98±29

Total 95 Fixed Effect Phase (p-value) Fixed Effect Possession (p-value)

50±5

10591±1076

223±117

30±14

838±296

105±33

0.0804

0.9219