Age-Related Differences in Lower-Limb Muscle Cross-Sectional Area and Torque Production in Boys With Duchenne Muscular Dystrophy

Mathur S, Lott DJ, Senesac C, Germain SA, Vohra RS, Sweeney HL, Walter GA, Vandenborne K. Age-related differences in lower-limb muscle cross-sectional area and torque production in boys with Duchenne muscular dystrophy.

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 (CSA_max) assessed by magnetic resonance imaging of quadriceps, plantarflexors (PFs) and dorsiflexors (DFs), peak isometric torque from dynamometry, and timed functional tests.

Results

The average CSA_max 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 CSA_max. The increase in quadriceps CSA_max was also distinctly different in boys with DMD compared with controls. Specific torque (ie, peak torque/CSA_max) 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.