Greater Association of Relative Thresholds Than Absolute Thresholds With Noncontact Lower-Body Injury in Professional Australian Rules Footballers: Implications for Sprint Monitoring

O'Connor, F., Thornton, H.R., Ritchie, D., Anderson, J., Bull, L., Rigby, A., Leonard, Z., Stern, S., Bartlett, J.D.

Purpose:
To examine the relationship between sprint workloads using relative vs absolute thresholds and lower-body soft-tissue and bone-stress injury incidence in professional Australian Rules Football (AF).

Methods:
Fifty-three professional AF athletes’ noncontact soft-tissue and bone-stress lower-body injuries (N = 62) were recorded, and sprint workloads were quantified over approximately 18 months using GPS. 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 (IRR) and model performances’ area under the curve (AUC) were reported.

Results:
Mean ± SD maximal velocity for the group was 31.5 ± 1.4, range 28.6–34.9 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 km·h⁻¹ and 1.7 km·h⁻¹ above the absolute speed threshold, respectively. Model AUC 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 IRR (2.54–3.29), than absolute thresholds (1.18–1.58).

Discussion:
Monitoring sprinting volume relative to an athlete’s maximal 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.

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