Physical Activity Correlates With Skeletal Muscle MRI Findings in Individuals With Duchenne Muscular Dystrophy.

Introduction/aims: Skeletal muscle magnetic resonance imaging (MRI) is a validated noninvasive tool to assess Duchenne muscular dystrophy (DMD) progression. There is interest in finding DMD biomarkers that decrease the burden of clinical trial participation, such as wearable devices. Our aim was to evaluate the relationship between activity, via accelerometry, and skeletal muscle MRI, particularly T mapping.

Methods: DMD children and young adults completed skeletal muscle MRI and were asked to wear an accelerometer on the dominant wrist for 7 days. MRI data included fat-suppressed transverse relaxation time (T) mapping of the calves and longitudinal relaxation time (T) mapping. Activity was assessed as vector magnitudes (VMs) and fraction of time (FOT) in activity groups (sedentary 1 or 2, low 1 or 2, moderate-to-vigorous physical activity (MVPA)).

Results: Participants (n = 22; median age 11.4 years, 41% ambulatory) wore the accelerometer for a median of 7 days. Longer T in multiple lower extremity muscles was negatively correlated with VMs per minute (tibialis posterior Spearman's rho = -0.68, p < 0.001), even when accounting for age, ambulatory status, or glucocorticoid use. Longer T of the tibialis posterior was positively correlated with FOT in sedentary 1 (rho = 0.49, p = 0.02) and negatively correlated with FOT in higher activity levels (low 1 (rho = -0.58, p = 0.004), low 2 (rho = -0.67, p = 0.002), MVPA (rho = -0.7, p < 0.001)).

Discussion: In individuals with DMD, longer T on skeletal muscle MRI of the calves moderately correlated with lower activity levels indicating the potential use of home accelerometry as a future clinical trial biomarker of skeletal muscle health and progression in DMD.