Deficits in rate of torque development are accompanied by activation failure in patients with knee osteoarthritis.

Aim of this study was to investigate if knee extensor maximal voluntary contraction (MVC) torque and rate of torque development (RTD) deficits are accompanied by neuromuscular activation failure in patients with knee osteoarthritis (KOA). Nineteen patients with unilateral KOA completed gradual MVCs, from which MVC torque, voluntary activation and maximal EMG activity were recorded, and explosive MVCs, from which RTD and rate of EMG rise were recorded. For gradual MVCs, MVC torque (-28%), voluntary activation (-6%) and maximal EMG activity (-30%) were lower on the involved than on the uninvolved side (p < 0.001). Asymmetries in MVC torque and maximal EMG activity were positively correlated (r = 0.70; p < 0.001). For explosive MVCs, involved-side RTD (-19%) and rate of EMG rise (-20%) were lower compared to the uninvolved side (p < 0.05-0.001). Asymmetries in RTD and rate of EMG rise were positively correlated (r = 0.61-0.80; p < 0.01). Deficits in isometric knee extensor strength were accompanied by neuromuscular activation failure during gradual MVCs and, more importantly, during the early phase of explosive MVCs. Such inability to rapidly activate the quadriceps may have functional consequences and warrants greater attention in the evaluation and rehabilitation of patients with KOA.