Effects of load magnitude, muscle length and velocity during eccentric chronic loading on the longitudinal growth of vastus lateralis muscle

Abstract

Abstract The present study investigated the longitudinal growth of the vastus lateralis (VL) muscle using four eccentric exercise protocols with different mechanical stimuli by modifying the load magnitude, lengthening velocity and muscle length at which the load is applied. Thirty-one participants voluntarily participated in this study in two experimental (EG) and one control group (CG). The first EG (n=10) exercised the knee extensors of one leg at 65% (low load magnitude) of the maximum isometric voluntary contraction (MVC) and the second leg at 100% MVC (high load magnitude) with 90°/s angular velocity, from 25° to 100° knee angle. The second EG (n=10) exercised one leg at 100% MVC, 90°/s, from 25° to 65° knee angle (short muscle length). The other leg was exercised at 100% MVC, 240°/s angular velocity (high muscle lengthening velocity) from 25° to 100°. In the pre-post measurements we examined the fascicle length of the VL at rest and the moment-angle relationship of the knee extensors. After 10 weeks of intervention we found a significant increase (~14%) of VL fascicle length compared to the CG, yet only in the leg that was exercised with high lengthening velocity. The findings provide evidence that not every eccentric loading causes an increase in fascicle length and that the lengthening velocity of the fascicles during the eccentric loading and particularly in the phase where the knee joint moment decreases (i.e. deactivation of the muscle) seems to be an important factor for longitudinal muscle growth.