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 [PL VM]) from the individual-component planes of PlayerLoad™ (anterior–posterior PlayerLoad™ [PL AP], medial–lateral PlayerLoad™ [PL ML] and vertical PlayerLoad™ [PL V]), together with locomotor activity (Total Distance Covered [TDC]) were determined in 15-min segments. Locomotor efficiency was calculated using the ratio of PL VM and TDC (PlayerLoad™ per metre). The proportion of variance explaining the within-match trends in PL VM, PL AP, AP ML, AP v, and TDC was determined owing to matches, individual players, and positional role.
Results
PL VM, PL AP, AP ML, AP v and TDC reduced after the initial 15-min match period ( p = 0.001; η 2 = 0.22–0.43, large effects). PL:TDC increased in the last 15 min of each half ( p = 0.001; η 2 = 0.25, large effect). The variance in PL VM 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.