The effect of downhill running conditions on muscle damage in recreationally active adults

Background: Downhill running (DR) has been used extensively to investigate recovery from muscle-damaging exercise. There is no consensus on the optimal conditions (duration, severity, intensity) for a DR protocol. The purpose of this research was to determine the most effective DR conditions to induce muscle damage. Methods: The research was comprised a 3x3 within-between participant design. Recreationally active males’ (n = 12) muscle damage was assessed using gold standard indirect markers (force loss and muscle soreness) at baseline, 24 and 48h post one of three DR conditions (a. 45min at -10% gradient b. 45min at -12% c. 30min at -15%). DR was completed on a motorised treadmill at 70% velocity of V̇O2peak achieved during an incremental exercise test to exhaustion. Results: Isometric force (p = .005, ηp2 = 0.45) and muscle soreness (p = .002, ηp2 = 0.49) were impaired 24h post-exercise; no difference (p > .05) was evident between conditions. At 48h the impairments in force loss and muscle soreness were no longer evident (p > .05) across all conditions. There was no difference (p = .82) in HR between the DR conditions. Findings: Independent of duration and gradient all conditions resulted in a similar response in force loss and muscle soreness, indicating muscle damage had occurred. Interestingly, the 30-min protocol produced the same response in less time, without requiring individuals to work at a greater intensity. Therefore, the 30-min condition is suggested as the most appropriate protocol for use in the scientific investigation of muscle damage from DR.