Purpose: We used magnetic resonance (MR) imaging and ultrasonography in combination with a dynamometer to assess physiological and functional aspects of the skeletal muscles after strenuous exercise that included eccentric contraction. Methods: Seven male subjects (mean age, 21.7 years) performed ankle plantar flexion that included eccentric contraction and underwent Diffusion-weighted MR imaging for calculation of the apparent Diffusion coefficient (ADC) of the triceps surae muscles. We used ultrasonography combined with a dynamometer to measure the displacement of the myotendinous junction (MTJ) of the medial gastrocnemius and maximal isometric force during ankle plantar flexion. We also assessed the level of muscle soreness of the calf using a visual analogue scale.We measured these parameters before exercise and one, 2, 3, 5, and 8 days after exercise and examined significant changes from the pre-exercise value using repeated-measures analysis of variance with Dunnett's test for each measurement parameter. Results: One day after exercise, we observed increased muscle soreness (P< 0.001) and decreased MTJ displacement (P<0.05); isometric force generation tended to decrease, but the change was not significant.Muscle soreness peaked 2 days after exercise (P< 0.001) and remained significantly increased until 5 days after exercise (P< 0.005). The medial gastrocnemius exhibited increased ADC value 3 days after exercise (P< 0.005), but the lateral gastrocnemius and the soleus showed no significant changes throughout this study. Conclusion: Our findings suggest that muscle damage induced by eccentric contraction manifests as muscle soreness and dysfunction early after exercise and later increases water Diffusion within damaged muscle.
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