The Use of Hamstring Fatigue to Reduce Quadriceps Inhibition After Anterior Cruciate Ligament Reconstruction

Arthrogenic muscle inhibition, an inability to fully activate the quadriceps muscles, has been persistently observed after anterior cruciate ligament reconstruction (ACLr) surgery. Reductions in quadriceps activation may be partly due to the flexion reflex pathway, hamstrings activation, and reciprocal quadriceps inhibition. Since central fatigue has been shown to modify hamstring excitability and change the hamstring reflex response, hamstring fatigue might alleviate quadriceps muscle inhibition by counteracting the flexion reflex. In this study, nine young adult athletes (age: M = 19.9 years, SD = 1.7) with unilateral ACLr and nine control athletes (age: M = 24.0 years, SD = 2.4) with no previous history of knee injury performed tempo squats to induce fatigue. The ACLr group tended to use hamstrings for more hip flexion and trunk forward flexion than the control group. We assessed each participant’s quadriceps inhibition through the central activation ratio (CAR), measured by twitch interpolation, befor...