Hamstrings fatigue does not improve quadriceps function in individuals with anterior cruciate ligament reconstruction

Our purpose was to investigate the immediate and prolonged effects of hamstrings fatigue on quadriceps neuromuscular function in individuals with anterior cruciate ligament reconstruction (ACLR) and matched uninjured controls.

Cross-Sectional.

Laboratory.

16 participants with a history of ACLR and 16 uninjured controls.

Quadriceps peak torque (PT), central activation ratio (CAR), early (RTD₁₀₀) and late (RTD₂₀₀) rate of torque development, vastus medialis and lateralis electromyographic (EMG) activity, and hamstrings-to-quadriceps co-activation assessed at baseline. Outcomes were evaluated pre-fatigue (PRE), immediately post-fatigue (POST), and 30min post-fatigue (POST30). The involved limbs of individuals with ACLR were assessed and control limbs were matched based on limb dominance.

Individuals with ACLR demonstrated lesser quadriceps PT (p = 0.004), CAR (p < 0.001), RTD₁₀₀ (p = 0.042), RTD₂₀₀ (p = 0.028), and vastus medialis EMG (p = 0.040) than controls, regardless of time. Quadriceps CAR (p < 0.001) and RTD₂₀₀ (p < 0.001) decreased at POST and POST30, whereas RTD₁₀₀ (p < 0.001) decreased at POST, regardless of group.

The observed reductions in quadriceps neuromuscular function may suggest involvement of central fatigue mechanisms, which should be explored prior to recommending hamstrings fatigue as a therapeutic intervention.