Isometric skeletal muscle force measurement in primary myopathies

Introduction: In myopathy patients, it is useful to measure skeletal muscle forces. Conventional methods require voluntary muscle activation, which can be unreliable. We evaluated a device for nonvoluntary force assessment. Methods: We tested 8 patients (unknown myopathy n = 2, inflammatory myopathy, facioscapulohumeral muscular dystrophy, mitochondrial myopathy, dysferlinopathy, multi-minicore disease, Becker-Kiener muscular dystrophy, n = 1 each). Isometric twitch torques of ankle dorsiflexors were measured after fibular nerve stimulation. Results: Six patients had decreased torques vs. 8 controls (men: median Newton-meter 1.6 vs. 5.7, women: 0.2 vs. 3.9, both P < 0.0001). Values correlated with Manual Muscle Test results (r = 0.73; r² = 0.53; P < 0.0001). In weak dorsiflexors, torque could be measured despite lower signal-to-noise ratios. In 2 patients with hypertrophy, we measured increased torques. Conclusions: Nonvoluntary muscle force assessment can be used in patients with myopathies, and values correlate with voluntary forces determined by traditional methods.