Ultrastructural evidence of exercise-induced muscle disruption (EIMD) following endurance exercise has traditionally been demonstrated through the use of skeletal muscle biopsy sampling. Noninvasive methods such as T2 and proton-density fat saturated magnetic resonance imaging (MRI) have been applied to examine EIMD, but these are limited by their sensitivity and dynamic range. Diffusion Tensor MRI (DT-MRI) measures the self-diffusion of water in biological tissues and can be used to visualize fiber patterns in various tissues including skeletal muscle. DT-MRI has previously been utilized to assess skeletal muscle abnormalities induced by traumatic injury (e.g., acute hematoma and muscle tears) and after high-force eccentric exercise; however, it remains unknown whether this method can be applied to detect EIMD after an acute bout of endurance running.
PURPOSE: To investigate changes in musculoskeletal structure using DT-MRI after an acute bout of downhill running previously shown to induce ultrastructural disruption.
METHODS: Ten healthy men (25 ± 1 y; VO2 peak = 52 ± 3 ml·kg-1·min-1) ran downhill on a treadmill (-10 degrees) for 45 min at 70% of maximal heart rate. DT-MRI measurements were performed using a GE 3T excite-HD MRI system using 15 diffusion encoding directions (8 NEX, FOV=20cm, TE/TR=67/6000, 64×64 matrix, 4mm thick, 0 skip, b=300s/mm2).
RESULTS: Isometric (238 ±12 vs. 209 ± 11 N/m) and isokinetic (194 ± 8 vs. 178 ± 5 N/m) peak torque decreased at 24 h post-exercise compared to baseline while serum creatine kinase activity increased (22 ± 3 vs. 106 ± 21 U/L) (all P<0.05). DT-MRI revealed a decrease in fractional anisotropy (FA) in the vastus lateralis at 24 h post-exercise compared to baseline (0.282 ± 0.006 vs. 0.262 ± 0.005 arbitrary units; P<0.05), which is indicative of changes in overall fibre organization.
CONCLUSION: These data suggest that DT-MRI may be a suitable technique to non-invasively detect, and possibly quantify, exercise-induced changes in skeletal muscle ultrastructure.
Supported by NSERC.