Patients with nemaline myopathy, a muscle disorder primarily affecting the thin filaments, suffer from weakness which is poorly understood. As disturbed excitation-contraction coupling has been suggested as a possible mechanism, the present study was designed to investigate whether the contractile properties of the knee-extensor muscles in patients from a single family with nemaline myopathy were different from able-bodied individuals. To assess central neural as well as more peripheral intrinsic aspects of muscle activation, isometric voluntary and electrically elicited quadriceps contractions were evoked at different knee angles. Interestingly, across the range of 30-70° of knee flexion, the capacity to achieve maximal voluntary activation of the muscles, assessed by a super-imposed stimulation technique, was significantly higher in patients compared with controls. Furthermore, the torque-frequency relation differed between groups, with the muscles of patients producing higher torques at low (twitch and 10Hz) stimulation frequencies relative to maximal (150Hz) stimulation than controls at both 30° and 60° of knee flexion. These results suggest that no impairment was present at relatively low activation frequencies. It may, however, be indicative for a reduced cross-bridge attachment as part of the excitation-contraction coupling specifically at high activation frequencies. In conclusion, the quadriceps weakness observed in this specific patient group cannot be explained by an impaired capacity to maximally activate these muscles. However, the data of relatively high torques produced at submaximal activation frequencies are compatible with the hypothesis that patients with nemaline myopathy may have an impaired acto-myosin interaction specifically at high levels of activation. © 2007 The Authors Journal compilation © 2007 Blackwell Publishing Ltd.