Exercise-related leg muscle signal changes: assessment using diffusion-weighted MRI

We aimed to detect physiologic changes of leg muscle signal on magnetic resonance (MR) diffusion-weighted imaging (DWI) in asymptomatic subjects after repetitive plantar flexion exercises. In this monocentric prospective study, DWI of both legs were performed at rest and after exercise periods (5 min, Ex(5): and 10 min, Ex(10)) in 20 active healthy subjects (mean age 31 years). The exercise consisted in repetitive plantar flexion of the right foot using elastic band, the patient being sited directly on the MR table. Both visual semiquantitative evaluations and quantitative (apparent diffusion coefficient, ADC; fractional anisotropy, FA) were performed in 5 leg compartments. Visually, signal changes involved mainly the fibular and gastrocnemius muscles and were considered intense after Ex(5) in 3 subjects, moderate only after Ex(5) in 10, and moderate only after Ex(10) in 4. No changes were visible in 3 subjects. Quantitative evaluation confirmed significant signal changes in the fibular (ADC: + 17.4%, p < 0.001; FA: -8.3%, p = 0.030) and gastrocnemius (ADC: + 13.7%, p < 0.001; FA: -11.4%, p < 0.001) muscles between rest and post-exercise MR. Plantar flexion exercises induce changes on DWI, especially in fibular and gastrocnemius muscles, which can be visually and quantitatively detectable in asymptomatic active subjects.