Objectives: 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.
Design: Cross-Sectional.
Setting: Laboratory.
Participants: 16 participants with a history of ACLR and 16 uninjured controls.
Main outcome measures: 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.
Results: 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.
Conclusions: 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.
Keywords: Anterior cruciate ligament; Centrally-mediated fatigue; Muscle inhibition; Quadriceps function.
Published by Elsevier Ltd.