Accumulated workloads and the acute: chronic workload ratio relate to injury risk in elite youth football players

Aim The purpose of this study was to investigate the relationship between physical workload and injury risk in elite youth football players. Methods The workload data and injury incidence of 32 players were monitored throughout 2 seasons. Multiple regression was used to compare cumulative (1, 2, 3 and 4-weekly) loads and acute: chronic (A:C) workload ratios (acute workload divided by chronic workload) between injured and non-injured players for specific GPS and accelerometer-derived variables: total distance (TD), high-speed distance (HSD), accelerations (ACC) and total load. Workloads were classified into discrete ranges by z-scores and the relative risk was determined. Results A very high number of ACC (>= 9254) over 3 weeks was associated with the highest significant overall (relative risk (RR) = 3.84) and non-contact injury risk (RR = 5.11). Non-contact injury risk was significantly increased when a high acute HSD was combined with low chronic HSD (RR = 2.55), but not with high chronic HSD (RR = 0.47). Contact injury risk was greatest when A: C TD and ACC ratios were very high (1.76 and 1.77, respectively) (RR = 4.98). Conclusions In general, higher accumulated and acute workloads were associated with a greater injury risk. However, progressive increases in chronic workload may develop the players' physical tolerance to higher acute loads and resilience to injury risk.