Voluntary and magnetically evoked muscle contraction protocol in males with Duchenne muscular dystrophy: Safety, feasibility, reliability, and validity.

Abstract

Clinical trials addressing treatments for Duchenne muscular dystrophy (DMD) require reliable and valid measurement of muscle contractile function across all disease severity levels. In this work we aimed to evaluate a protocol combining voluntary and evoked contractions to measure strength and excitability of wrist extensor muscles for safety, feasibility, reliability, and discriminant validity between males with DMD and controls. Wrist extensor muscle strength and excitability were assessed in males with DMD (N=10; mean ± standard deviation: 15.4 ± 5.9 years of age), using the Brooke Upper Extremity Rating Scale (scored 1-6), and age-matched healthy male controls (N=15; 15.5 ± 5.0 years of age). Torque and electromyographic (EMG) measurements were analyzed under maximum voluntary and stimulated conditions at two visits. A protocol of multiple maximal voluntary contractions (MVCs) and evoked twitch contractions was feasible and safe, with 96% of the participants completing the protocol and having a less than 7% strength decrement on either measure for both DMD patients and controls (P ≥ .074). Reliability was excellent for voluntary and evoked measurements of torque and EMG (intraclass correlation coefficient [ICC]over 0.90 and over 0.85 within and between visits, respectively). Torque, EMG, and timing of twitch-onset measurements discriminated between DMD and controls (P < .001). Twitch contraction time did not differ significantly between groups (P=.10). Findings from this study show that the protocol is a safe, feasible, reliable, and a valid method to measure strength and excitability of wrist extensors in males with DMD.