Greater association of relative thresholds than absolute thresholds with noncontact lower-body injury in professional australian rules footballers: Implications for sprint monitoring

Sprint capacity is an important attribute for team-sport athletes, yet themost appropriate method to analyze it is unclear. 

Purpose: To examine the relationship between sprint workloads using relative versus absolute thresholds and lower-body soft-tissue and bone-stress injury incidence in professional Australian rules football. 

Methods: Fifty-three professional Australian rules football athletes' noncontact soft-tissue and bone-stress lower-body injuries (N = 62) were recorded, and sprint workloads were quantified over ∼18 months using the global positioning system. Sprint volume (m) and exposures (n) were determined using 2 methods: Absolute (>24.9 km h^-1) and relative (≥75%,≥80%,≥85%,≥90%,≥95% of maximal velocity). Relationships between threshold methods and injury incidence were assessed using logistic generalized additive models. Incidence rate ratios and model performances' area under the curve were reported. 

Results: Mean (SD) maximal velocity for the group was 31.5 (1.4), range 28.6 to 34.9 km h^-1. In comparing relative and absolute thresholds, 75% maximal velocity equated to ∼1.5 km h^-1 below the absolute speed threshold, while 80% and 85% maximal velocity were 0.1 and 1.7 km h^-1 above the absolute speed threshold, respectively. Model area under the curve ranged from 0.48 to 0.61. Very low and very high cumulative sprint loads≥80% across a 4-week period, when measured relatively, resulted in higher incidence rate ratios (2.54-3.29), than absolute thresholds (1.18-1.58). 

Discussion: Monitoring sprinting volume relative to an athlete'smaximal velocity should be incorporated into athlete monitoring systems. Specifically, quantifying the distance covered at >80% maximal velocity will ensure greater accuracy in determining sprint workloads and associated injury risk.