Running fatiguing protocol affects peak torque joint angle and peak torque differently in hamstrings vs. quadriceps

Purpose: The aim of the current study was to investigate the effects of a running fatiguing protocol on the peak torque joint angle and the peak torque in hamstrings vs. quadriceps. Methods: Twenty-one male runners underwent a running fatiguing protocol consisting of 40 min at a speed corresponding at first ventilatory threshold. Before and after the fatiguing protocol, isokinetic concentric and eccentric hamstrings and concentric quadriceps peak torque was measured at 60 and 300 deg s−1. The peak torque joint angle (i.e. the angle at which the peak torque was exerted) was recorded. The conventional Hconc:Qconc ratio and the functional Hecc:Qconc ratio were also calculated. Results: The peak torque joint angle increased (i.e. shifted toward shorter muscle length) in hamstrings in eccentric at 60 deg s−1 (ES = 1.35) and at 300 deg s−1 (ES = 0.71) and in concentric modality at 300 deg s−1 (ES = 0.50) but not at 60 deg s−1 (ES = 0.23). No change occurred in quadriceps at 60 deg s−1 (ES = 0.15) and 300 deg s−1 (ES = 0.20). Peak torque deteriorated in both hamstrings and quadriceps, irrespective of the testing modality (ES 0.95–1.90) Functional Hecc:Qconc ratio decreased at 60 deg s−1 (ES = 0.74) and 300 deg s−1 (ES = 0.85). No change in conventional Hconc:Qconc ratio occurred at 60 deg s−1 (ES = 0.12) and 300 deg s−1 (ES = 0.14). Conclusion: The fatigue-induced changes in peak torque joint angle in hamstrings but not in quadriceps and the simultaneous decrements in the functional Hecc:Qconc ratio may point a reduced hamstrings resistive capacity, with implications for hamstrings strain injury risk.