Effect of immobilization and retraining on torque-velocity relationship of human knee flexor and extensor muscles

The effect of 2 weeks immobilization of the uninjured right knee and 10 weeks of retraining on muscle torque-velocity characteristics was investigated in nine young subjects. Left and right knee extension and flexion maximal voluntary isometric torque (T_max) and dynamic torque at 60°·s^–1 (T₆₀) and 180°·s^–1 (T₁₈₀) were measured before (PRE) and after immobilization (POST) and after 3 (R3) and 10 (R10) weeks of dynamic retraining. The torque-velocity relationship was quantified by expressing T₆₀ and T₁₈₀ relative to T_max (NT₆₀ and NT₁₈₀, respectively). For the right extensor muscles, percutaneous biopsy samples were obtained from the vastus lateralis muscle and fibre type distribution was measured. POST extension and flexion torque (mean of T_max, T₆₀ and T₁₈₀) decreased by 27% and 11%, respectively. During the course of the experiment, the changes in NT₆₀ and NT₁₈₀ were similar. POST extensor muscle NTV (mean of NT₆₀ and NT₁₈₀) was decreased significantly (12%, P<0.05), but no significant change was found for flexor muscle NTV (+3%). At R3 T_max, dynamic torque and NTV were restored to normal. Unlike isometric torque, NTV did not change from R3 to R10. No changes in fibre type distribution were found. The adaptation of muscle length is suggested as the mechanism to explain the change in NTV. Electronic Publication