Determination of muscle fatigue index for strength training in patients with Duchenne dystrophy

Abstract

Introduction: Muscle weakness is the most prominent impairment in Duchenne muscular dystrophy (DMD) and often involves the loss of functional ability as well as other limitations related to daily living. Thus, there is a need to maintain muscle strength in large muscle groups, such as the femoral quadriceps, which is responsible for diverse functional abilities. However, the load and duration of training for such rehabilitation has proven to be a great unknown, mainly due to the undesired appearance of muscle fatigue, which is a severe factor for the injury of muscle fibers. Objectives: The aim of the present study was to determine a fatigue index by means of surface electromyography (EMG) for the parameterization of muscle strengthening physiotherapy training. Methods: A cross-sectional study (case series) was carried out involving four patients with DMD. Three pairs of surface electrodes were placed on the motor point of the Rectus femoris, Vastus lateralis and Vastus medialis of the dominant limb, maintaining the knee at 60º of flexion. The participants were instructed to perform the extension movement of this joint at four strength levels (100%, 80%, 60% and 40% of maximal voluntary isometric contraction). Results: The slope of the linear regression line was used for the determination of the fatigue index, performed by Pearson’s test on the median frequency of each strength level. Conclusion: Electromyographic measurements of the strength index for muscle training proved to be a simple accessible assessment method, as well as an extremely valuable tool, allowing the design of a muscle strength training program with an individualized load threshold.