Early functional and morphological changes of calf muscles in delayed onset muscle soreness (DOMS) assessed with 7T MRI.

Background: To assess morphological and functional alterations of the skeletal muscle in exercise-induced delayed onset muscle soreness (DOMS) using 7 Tesla (T) magnetic resonance imaging (MRI).

Methods: DOMS was induced in 16 volunteers performing an eccentric exercise protocol of the calf muscles of one randomized leg. 7 T MRI including T1w- (0.18×0.18×1mm), T2w-images (0.2×0.2×2mm), T2-maps (0.5×0.5×5mm), and susceptibility weighted imaging (SWI, 0.7×0.7×0.7 mm) were acquired at baseline, directly (t1) and 60 hours (t2) after the exercise. T2 signal intensity (SI), T2 values [ms], T1 SI and SWI were assessed in the medial (MG) and lateral gastrocnemius muscle (LG) and in the soleus muscle (SM). In addition, the serum creatine kinase (CK) activity, range of motion (ROM) of the ankle, calf circumference, and muscle soreness were assessed at each time point.

Results: Directly after exercise (t1), T2 SI (p=0.04) and T2 values (p=0.03) increased significantly in the LG. No changes of SI and T2 values for MG and SM were present at t1. At t2, T2 SI and T2 values of LG (p=0.001, p=0.02) and MG (p=0.04, p=0.03) increased significantly compared to baseline. T1 SI did not change in any muscle at any time point. In SWI, no signs of intramuscular signal drop could be detected. Clinical parameters confirmed the induction of DOMS, with a significant increase of CK (p=0.03), muscle soreness (p<0.001), calf circumference (p=0.001), and respective a decrease of ROM (p=0.04).

Conclusions: 7 T MRI has the potential to visualize microstructural muscle damage immediately after an exercise that induces DOMS. No changes in susceptibility which could, for example, reflect micro-hemorrhage, could be detected with SWI immediately after exercise or in DOMS. Ultra-high field MRI may potentially be used in sports medicine to monitor intramuscular structural changes, allowing for modification of training intensity or to implement appropriate therapeutic strategies.