Purpose: Hamstrings injury/reinjury is common, but functional reasons for this remain unclear. This study identified bilateral differences in swing phase running biomechanics and isokinetic strength, between the previously hamstring-injured and uninjured limbs of male athletes involved in sprint-based sports. Methods: Athletes, injury-free during testing, underwent three-dimensional motion analyses to determine bilateral joint kinematics and kinetics during submaximal sprinting. Various hip and knee isokinetic strength tests were performed bilaterally using a Biodex dynamometer. Peak torque (PT) and total work (TW; normalized to body mass) were collected isokinetically from concentric hamstrings (CH), concentric quadriceps (CQ), concentric hip flexors (CHF), and eccentric hamstrings (EH). Three PT and TW ratios were created, namely, CH/CQ, EH/CQ, and EH/CHF, and were compared between the previously injured and uninjured limbs. Results: Lower limb swing phase kinematics and kinetics were similar. Only peak hip flexion angle in late swing was significantly reduced (1.9°) in the previously injured limb. EH PT was decreased (26.2 N·m/kg) and occurred at shorter hamstring lengths on the previously injured side, whereas CQ TW was increased by 13.6 J/kg. EH/CQ and EH/CHF ratios for PT and TW were reduced on the previously injured limbs. Conclusions: Although swing phase biomechanics of submaximal sprinting were similar between limbs, the previously injured hamstrings did display significant weakness eccentrically. Residual eccentric weakness may predispose this muscle group to reinjury during late swing, compared with the uninjured limb, because the functional eccentric demand on both limbs was similar. Furthermore, the EH/CHF ratios may better reflect muscle function during sprinting, having the potential to influence rehabilitation to prevent reinjury.
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