Rate of torque development as an indirect marker of muscle damage in the knee flexors

Purpose: The aim of the study was to examine the changes in the rate of torque development (RTD) as indirect marker of muscle damage following a knee flexion exercise-induced muscle damage protocol in healthy individuals. Methods: Ten participants (24.8 ± 5.3 years) performed 60 maximal knee flexion eccentric contractions and were evaluated before 0, 24, 48, and 72 h after exercise protocol for maximal isometric and concentric isokinetic strength, optimum angle, RTD, muscle soreness, range of motion (ROM) and biceps femoris and semitendinosus muscle thickness (MT), and echo intensity (EI). RTD was analyzed at 0–50 ms (RTD_0–50), 0–100 ms (RTD_0–100), 100–200 ms (RTD_100–200) windowing, and peak RTD (RTD_peak). Results: RTD_0–50 was decreased (p < 0.05) after 24 h. RTD_0–100, RTD_100–200, and muscle soreness were decreased after 24, 48, and 72 h after exercise (p < 0.05). RTD_peak, maximal isometric and concentric isokinetic strength decreased and biceps femoris and semitendinosus MT increased (p < 0.05) at all time points after eccentric exercise. ROM was decreased (p < 0.05) 48 and 72 h after exercise. Semitendinosus EI was increased (p < 0.05) 72 h after exercise. Optimum angle was not changed after exercise. Conclusion: The knee flexor muscle RTD measured at different intervals were changed after the eccentric exercise protocol and may be used as an indirect marker of muscle damage.