Dynamic DTI (dDTI) shows differing temporal activation patterns in post-exercise skeletal muscles

Object To assess post-exercise recovery of human calf muscles using dynamic diffusion tensor imaging (dDTI). Materials and methods DTI data (6 directions, b = 0 and 400 s/mm 2 ) were acquired every 35 s from seven healthy men using a 3T MRI, prior to (4 volumes) and immediately following exercise (13 volumes, ~7.5 min). Exercise consisted of 5-min in-bore repetitive dorsiflexion-eversion foot motion with 0.78 kg resistance. Diffusion tensors calculated at each time point produced maps of mean diffusivity (MD), fractional anisotropy (FA), radial diffusivity (RD), and signal at b = 0 s/mm 2 (S 0 ). Region-of-interest (ROI) analysis was performed on five calf muscles: tibialis anterior (ATIB), extensor digitorum longus (EDL) peroneus longus (PER), soleus (SOL), and lateral gastrocnemius (LG). Results Active muscles (ATIB, EDL, PER) showed significantly elevated initial MD post-exercise, while predicted inactive muscles (SOL, LG) did not ( p < 0.0001). The EDL showed a greater initial increase in MD (1.90 × 10 −4 mm 2 /s) than ATIB (1.03 × 10 −4 mm 2 /s) or PER (8.79 × 10 −5 mm 2 /s) ( p = 7.40 × 10 −4 ), and remained significantly elevated across more time points than ATIB or PER. Significant increases were observed in post-exercise EDL S 0 relative to other muscles across the majority of time points ( p < 0.01 to p < 0.001). Conclusions dDTI can be used to differentiate exercise-induced changes between muscles. These differences are suggested to be related to differences in fiber composition.