Relationship between muscle strength and motor function in Duchenne muscular dystrophy

Measuring muscle strength and motor function is part of Duchenne muscular dystrophy (DMD) assessment. However, the relationship between these variables is controversial. Objective: To investigate the relationship between muscle strength and motor function and between these variables and age. Method: Muscle strength was measured by Medical Research Council (MRC) scale and motor function, by Motor Function Measure (MFM), in 40 non-ambulatory patients. Spearman tests investigated the relationships between muscle strength, motor function and age. Results: Total MRC and MFM scores were strongly related to each other (r = 0.94; p < 0.001), but not to age (r = -0.19, r = -0.31, respectively; p > 0.05). Strong and moderate relationships between partial muscle strength and motor function scores were found. Higher correlation coefficients were found between total scores and Dimensions 2 (axial/ proximal control) and 3 (distal control) of MFM. Conclusion: Muscle strength and motor function are strongly correlated and seem to decrease proportionally in DMD.