The within-match patterns of locomotor efficiency during professional soccer match play : implications for injury risk?

Objectives: The principle aim of the current study was to examine within-match patterns of locomotor efficiency in Professional Soccer, determined as the ratio between tri-axial accelerometer data (PlayerLoad™) and locomotor activities. Between match variability and determinants of PlayerLoad™ during match play were also assessed. Design: A single cohort, observational study. Methods: Tri-axial accelerometer data (PlayerLoad™) was recorded during 86 competitive soccer matches in 63 English championship players (574 match observations). Accelerometer data accumulated (PlayerLoad Vector Magnitude [PLVM]) from the individual-component planes of PlayerLoad™ (anterior-posterior PlayerLoad™ [PLAP], medial-lateral PlayerLoad™ [PLML] and vertical PlayerLoad™ [PLV]), together with locomotor activity (Total Distance Covered [TDC]) were determined in 15-min segments. Locomotor efficiency was calculated using the ratio of PLVM and TDC (PlayerLoad™ per metre). The proportion of variance explaining the within-match trends in PLVM, PLAP, APML, APv, and TDC was determined owing to matches, individual players, and positional role. Results: PLVM, PLAP, APML, APv and TDC reduced after the initial 15-min match period (P = 0.001; η2 = 0.22-0.43, large effects). PL:TDC increased in the last 15 minutes of each half (P = 0.001; η2= 0.25, large effect). The variance in PLVM during soccer match-play was explained by individual players (63.9%; P = 0.001) and between-match variation (21.6%; P = 0.001), but not positional role (14.1%; P= 0.364). Conclusions: Locomotor efficiency is lower during the latter stages of each half of competitive soccer match-play, a trend synonymous with observations of increased injury incidence and fatigue in these periods. Locomotor efficiency may be a valuable metric to identify fatigue and heightened injury risk during soccer training and match-play.