Strenuous resistance exercise effects on magnetic resonance diffusion parameters and muscle-tendon function in human skeletal muscle

Purpose: To assess the effects of strenuous exercise on magnetic resonance diffusion parameters and muscle-tendon complex function in skeletal muscle. Materials and Methods: Six men performed ankle plantar flexion exercises with eccentric contraction. The fractional anisotropy (FA), λ ₁, λ ₂, λ ₃, mean diffusivity (MD), and T ₂ values in the triceps surae muscles were measured by magnetic resonance diffusion tensor and spin-echo imaging. Passive torque of plantar flexors, maximal voluntary isometric plantar flexion torques (MVIP), and Achilles tendon stiffness during MVIP were measured by combined ultrasonography and dynamometry. Plasma creatine kinase and muscle soreness were also assessed. These parameters were measured before and 1-8 days postexercise. Results: The medial gastrocnemius exhibited significantly decreased FA 2-5 days after, increased λ ₂ 3 days after, and increased λ ₃ 2 and 3 days after exercise. This muscle also showed significantly increased MD and T ₂ values 3 days postexercise. MVIP significantly decreased 2 and 3 days postexercise, while passive torque significantly increased 2 days postexercise. Creatine kinase and muscle soreness increased 3-5 days and 1-5 days postexercise, respectively. Conclusion: Exercise-induced muscle damage manifested as significant changes in muscle diffusion parameters with muscle-tendon complex dysfunction and delayed-onset muscle soreness.