The effect of fatigue on peak strain of hamstring muscles in dominant and non-dominant sides during sprinting: a pre-post intervention study

Although fatigue is widely recognized as a risk factor for hamstring strain injuries, the mechanisms by which fatigue influences these injuries remain unclear. It is also uncertain whether fatigue differentially affects the risk factors for hamstring strain between lower limbs. Nineteen male track-and-field athletes underwent a fatigue intervention, with optimal muscle length assessed pre- and post-fatigue. Key biomechanical parameters during sprinting were also analyzed before and after fatigue. Post-fatigue, the non-dominant limb showed significant reductions in optimal lengths across all three biarticular hamstring muscles (p < 0.01; Cohen’s d = 0.95–1.07), with greater changes than the dominant limb (p < 0.05; $${\eta}_{p}^{2}$$ = 0.16–0.24). No significant differences were observed in maximal hip–knee angles, peak muscle lengths, or the timing of peak muscle strain (p > 0.05). However, the non-dominant limb exhibited increased peak strain in the long head of the biceps femoris and semimembranosus (p < 0.05; Cohen’s d = 0.46–0.52), but not in the semitendinosus (p = 0.06; Cohen’s d = 0.90). No significant inter-limb differences were observed in the strain changes of the hamstring biarticular muscles (p > 0.05). Fatigue was not associated with changes in sprint-phase peak lengths of the non-dominant biarticular hamstring muscles; however, it was accompanied by a reduction in optimal length, which may have increased peak strain. Clinically, monitoring fatigue-related changes in hamstring functional properties and addressing potential inter-limb asymmetries may be relevant for injury prevention and rehabilitation. The same fatigue protocol was not associated with increased peak strain on the dominant side, indicating a potential limb-specific susceptibility to fatigue-related strain increases.