Effects of High-Velocity Versus Low-Velocity Resistance Training on Muscle Echo Intensity in Healthy Young Women: A Randomized Controlled Trial

Background: Improving muscle quality to prevent and treat muscle dysfunction is critical. However, effective measures to improve muscle quality remain poorly understood. We investigated the effects of high- and low-velocity resistance training (RT) on muscle quality, mass, and function before and after an 8-week intervention. Hypothesis: High-velocity RT would improve muscle quality more effectively than low-velocity RT. Study Design: Randomized controlled trial. Level of Evidence: Level 1. Methods: A total of 33 healthy young women (23.1 ± 2.2 years) were assigned randomly to high-velocity (n = 16) or low-velocity (n = 17) groups. Both groups underwent concentric knee extension RT with a 60% 1-repetition maximum (1RM) load, performing 10 repetitions of 4 sets, 3 times per week for 8 weeks. The high-velocity group was instructed to complete each repetition as quickly as possible (mean repetition duration of 0.5 seconds), while the low-velocity group was required to execute each repetition in 3 seconds. Before and after the 8-week intervention, quadriceps femoris echo intensity (EI), muscle thickness (MT), isokinetic peak torque (60 and 300 deg/s), rate of velocity development (RVD) at 300 deg/s, and 1RM were assessed. Split-plot factorial design analysis of variance was used to compare the group × time interaction. Results: A group×time interaction was observed for EI ( P < 0.01). Only the high-velocity group showed a significant reduction in EI after the intervention. MT revealed a main effect of time ( P < 0.01), with both groups significantly increasing MT. RVD showed a group × time interaction ( P < 0.05), with significant increase only in the high-velocity group. Isokinetic peak torque and 1RM showed main effects of time ( P < 0.01), with significant increases in both groups. Conclusion: High-velocity RT may be superior to low-velocity RT in enhancing muscle quality and RVD. Clinical Relevance: These results emphasize the importance of RT velocity for muscle quality improvement.