The Influence of Player Interchange on the Cumulative and Residual Physical Fatigue Response to Soccer- Specific Activity.

Introduction Soccer match-play comprises a limited number of substitutions and players are frequently exposed to a high frequency of games and, consequently, short recovery. This high physical demand can increase the risk of injury (Carling et al., 2015). Increased player interchanges, in other intermittent sports, have been associated with a lower physiological load (Moss et al., 2015) and reduced risk of knee flexor (KF) strain injuries (Orchard et al., 2012). In 2015, the International Football Association Board identified the potential merit of a player interchange strategy by approving the use of an unlimited "return sub" ruling at grassroots level soccer. The aim of this study was to assess the influence of a player interchanges on reducing the physical fatigue response to a soccer-specific exercise protocol ([SSEP] Page et al., 2016). Methods Thirteen male soccer players (age 23.2 ± 4.6 yrs) completed, in a counterbalanced order, a control trial (CONT) comprising 6 x 15 min bouts of the SSEP with a 15 min half time period, and an interchange trial (INT) comprising 4 x 15 min bouts of the SSEP, with 15 min passive recovery intervening bouts. Heart rate (HR), rating of perceived exertion (RPE), uni-axial and tri-axial PlayerLoadTM, and mean (EMGmean) and peak (EMGpeak) bicep femoris electromyography were measured during each trial. Isokinetic eccentric KF peak torque (PT) was also measured pre-, post-, and 48-hours post-trial. Results and Discussion Significantly lower (P=0.003) HR values were reported during INT (143± 11 b.min-1) com- pared to CONT (153 ± 13 b.min-1). INT (12 ± 2 a.u) RPE was significantly (P< 0.001) lower than CONT (13 ± 2 a.u). The interchange trial also elicited significant (P< 0.05) changes in PlayerLoadTM metrics. PT values were significantly (P=0.04) higher during INT (180 degs.s-1= 152.11 ± 25.90 Nm; 300 degs.s-1= 154.13 ± 21.52 Nm) compared to CONT (180 degs.s-1= 141.27 ± 26.29 Nm; 300 degs.s-1= 144.12 ± 21.30 Nm). There was no diference (P> 0.05) in the EMG data between the two trials. Conclusion Player interchanges result in a reduced cumulative physiological, perceptual, and external load response to soccer-specific activity, with implications for reduced injury risk and im- proved performance. The post-exercise rate of recovery associated with the KF PT data was greater in the interchange trial, with implications for training periodization and injury management (Orchard et al., 2012).