Mechanical, Neuromuscular, and Hypertrophic Adaptations Through Different Velocity Loss Thresholds With Moderate Loads in Full Squat

Abstract

This study aimed to compare the effects of 4 different velocity loss (VL) thresholds (0, 10, 20 and 40%) on hypertrophic, mechanical, and neuromuscular adaptations during a full-squat (SQ) training program, using loads ranging from 55 to 70% of 1-repetition maximum (1RM). Fifty-one moderately resistance-trained men were randomly assigned to 4 training groups, which differed in the VL threshold achieved within the set (VL0, VL10, VL20, and VL40). Subjects completed 16 SQ sessions (2 per week). Pre- and post-intervention assessments included the following: (a) cross-sectional area (CSA) of the vastus lateralis muscle, (b) countermovement jump, (c) maximal isometric SQ contraction, (d) incremental loading SQ test, and (e) fatigue SQ test. All groups significantly increased muscle CSA (p < 0.01, group × time interaction p = 0.18; effect size: VL0: 0.19; VL10: 0.22; VL20: 0.19; VL40: 0.47). Significant group × time interactions were observed for 1RM (p = 0.03) and the velocity attained against heavy loads (p = 0.02), with VL20 obtaining the greatest gains. Effect sizes in the different strength variables were as follows: VL0: 0.50-1.70; VL10: 0.53-2.34; VL20: 0.81-2.72; VL40: 0.52-0.86. Moderate-load resistance training with moderate VL thresholds elicits the greatest strength gains, whereas higher VL thresholds were associated with greater increases in muscle CSA, despite no significant group × time interaction, and yielded comparatively lower strength improvements, highlighting the need to consider VL when applying velocity-based resistance training.