Does wearing a functional knee brace affect hamstring reflex time in subjects with anterior cruciate ligament deficiency during muscle fatigue?

OBJECTIVE To evaluate the effects of wearing a functional knee brace and muscle fatigue on hamstring reflex time in subjects with anterior cruciate ligament (ACL) deficiency. DESIGN Repeated-measures clinical trial. SETTING Outpatient physical therapy department. PARTICIPANTS Sixteen subjects with ACL deficiency. INTERVENTION Subjects tested with and without a functional knee brace before and after an exercise protocol designed to fatigue the knee muscles. MAIN OUTCOME MEASURE Latency of hamstring reflex muscle activity after sudden perturbation of the knee. RESULTS Wearing a knee brace shortened the hamstring reflex latency regardless of fatigue (F(1,15)=20.62, P<.001). Muscle fatigue lengthened the hamstring reflex time regardless of the bracing condition (F(1,15)=7.57, P<.015). CONCLUSION Wearing a functional knee brace facilitated hamstring muscle reflex, but muscle fatigue lengthened the hamstring reflex latency. Subjects with ACL deficiency should not rely on the knee brace to facilitate hamstring reflex for joint protection during prolonged sporting activities when muscles are fatigued.