Using DT-MRI and 31P-MRS to Assess Muscle Damage Following Unaccustomed Eccentric Exercise

Abstract

PURPOSE: To detect the musculoskeletal structure and metabolism changes in vivo by diffusion tensor magnetic resonance imaging (DT-MRI) and 31P-Magnetic resonance spectroscopy (31P-MRS) after a single bout of eccentric exercise. METHODS: Thirty two male Sprague Dawley rats (body weight 238±15g) were randomly divided into either a sham group (n=8) or a downhill running group (n=24). Rats in the downhill running group ran 120 min on treadmill at a speed of 20 m/min at -16 degrees grade. DT-MRI and 31P-MRS were performed in right lower limb at pre-exercise (sham), immediately, 24 hr and 48 hr post-exercise at 7T MR. The MR sequence included RARE T2, RARE T1and EPI-DTI. MRS observational indices included the peak areas of inorganic phosphate concentration (Pi), phosphocreatine concentration (PCr) and the ratio of Pi/PCr. The morphological changes were confirmed by histological and immunohistochemical methods. One-way ANOVAs and Tukey’s test were used to assess the differences among different time points. RESULTS: On diffusion tensor tractography images, a single bout of downhill running significantly disrupted muscle fiber structure. The peak areas of Pi were significantly higher after exercise (pre-exercise: 4.1±0.8 mM; 0 hr post-exercise: 4.7±1.4 mM; 24 hr post-exercise: 6.6±1.9 mM; 48 hr post-exercise: 6.1±1.7 mM; all P<0.01). Muscle PCr did not differ between pre- and post-exercise; consequently, Pi/PCr values were significantly higher following EIMD (pre: 0.14±0.05; 0h post: 0.18±0.05; 24h post:0.22±0.08; 48h post: 0.2±0.08; all P<0.05). According to the histological detection, Z-band streaming was higher post-exercise compared with baseline (all P<0.05). The histopathological indices of damage coincided with changes in DT-MRI parameters of fractional anisotropy and apparent diffusion coefficient. CONCLUSIONS: The data suggest that exercise-induced muscle damage was accompanied by structural and metabolic alterations in skeletal muscle following a single bout of downhill running.The ability of DT-MRI and 31P-MRS to accurately detect these changes in vivo makes them promising approaches to evaluate skeletal muscle damage after unaccustomed exercise. (This research is supported by the National Natural Science Foundation of China, Grant#: 81301195)