Abstract

Objective: To examine the relationship between lower-extremity muscle cross-sectional area, muscle strength, specific torque, and age in ambulatory boys with Duchenne muscular dystrophy (DMD) compared with controls. Design: Observational cross-sectional study. Setting: University research setting. Participants: Volunteer sample of boys with DMD (n=22) and healthy control boys (n=10), ages 5 through 14 years. Interventions: Not applicable. Main Outcome Measures: Maximal muscle cross-sectional area (CSAmax) assessed by magnetic resonance imaging of quadriceps, plantarflexors (PFs) and dorsiflexors (DFs), peak isometric torque from dynamometry, and timed functional tests. Results: The average CSAmax of the triceps surae muscle group was approximately 60 % higher in boys with DMD compared with controls (39.1 ± 13.6 cm2 vs 24.5 ± 9.3 cm2; P = .002), while the tibialis anterior muscle showed age-appropriate increases in CSAmax. The increase in quadriceps CSAmax was also distinctly different in boys with DMD compared with controls. Specific torque (ie, peak torque/CSAmax) was impaired in all 3 muscles groups, with the knee extensor (KE) and PF muscles showing 4-fold, and the DF muscles 2-fold, higher values in controls compared with boys with DMD. Large age-related gains in specific torque were observed in all 3 muscle groups of control subjects, which were absent in ambulatory boys with DMD. Correlations were observed between performance on functional tasks and quadriceps and PF torque production (r = −.45 to −.57, P < .05), but not with DF strength. Conclusions: Age-related changes in muscle cross-sectional area and specific torque production in lower-extremity muscles showed distinctly different patterns in the KE, PF, and DF muscles of boys with DMD compared with controls. Verf.-Referat