CAPTURING COMPLEX,NON-LINEAR TEAM BEHAVIOURS DURING COMPETITIVE FOOTBALL PERFORMANCE

This study investigated changes in the complexity （magnitude and structure of variability） of the collective behaviours of association football teams during competitive performance. Raw positional data from an entire competitive match between two professional teams were obtained with the ProZone tracking system. Five compound positional variables were used to investigate the collective patterns of performance of each team including： surface and geometrical centre. Analyses involve the coefficient （ApEn）, as well as the linear association between both area, stretch index, team length, team width, of variation （%CV） and approximate entropy parameters. Collective measures successfully captured the idiosyncratic behaviours of each team and their variations across the six time periods of the match. Key events such as goals scored and game breaks （such as half time and full time） seemed to influence the collective patterns of performance. While ApEn values significantly decreased during each half, the %CV increased. Teams seem to become more regular and predictable, but with increased magnitudes of variation in their organisational shape over the natural course of a match.

Changes in markers of body composition of professional male soccer players during pre-season

To evaluate changes achieved in whole-body and regional(upper limbs,lower limbs,and trunk)estimates of body composition,twenty professional male soccer players(7 defenders,7 midfielders,6 forwards)underwent dualenergy x-ray absorptiometry(DXA)analysis at the beginning and end of pre-season.Measures included:mass,fat mass(FM),fat-free mass(FFM),and body fat per cent(BF%).Players’activity during on-field training sessions was monitored using Global Positioning System(GPS)units,with GPS data used to obtain estimations of energy expenditure(EE).Whole-body mass remained unchanged across the pre-season.Moderate significant increases and decreases were achieved in whole-body FFM(Pre:59.58±5.27 kg;Post:60.61±5.18 kg;p=0.001;d=0.87)and FM(Pre:10.60±1.88 kg;Post:9.56±1.81 kg;p=0.001;d=0.85),respectively.Moderate significant decreases were achieved in whole-body BF%(Pre:14.4±2.3%;Post:12.9±2.0%;p<0.001;d=0.94).No significant inter-positional differences were observed for the changes achieved in any global or regional estimate of body composition.Total EE was significantly correlated withΔFM(r=0.65,p=0.002),ΔFFM(r=0.46,p=0.03),andΔBF%(r=0.67,p=0.002).The total EE of pre-season training accounted for 42%,21%,and 45%of the variance inΔFM,ΔFFM,andΔBF%,respectively.These findings suggest that the pre-season period is a suitable time for initiating favourable alterations in body composition following the off-season in elite soccer players.