Knee flexion range of motion does not influence muscle hypertrophy of the quadriceps femoris during leg press training in resistance-trained individuals

Abstract

This study investigated the effect of knee flexion range of motion (ROM) during the leg press exercise on quadriceps femoris muscle hypertrophy in resistance-trained individuals. Twenty-three participants (training age: 7.2 ± 3.5 years) completed a within-participant design, performing four sets of unilateral leg presses to momentary failure twice weekly for 8 weeks. In one leg, the knee flexion range of motion (ROM) was fixed at approximately 5-100°, while for the other leg, participants used their maximum individualized ROM (5-154 ± 7.8°). Quadriceps muscle thickness was assessed via B-mode ultrasonography in the proximal, central, and distal regions of the mid- and lateral thighs. Bayesian analyses were conducted to quantify treatment effects and provide inferential estimates using credible intervals and Bayes Factors (BF). Univariate and multivariate analyses indicated 'moderate' (BF = 0.14 to 0.22) and 'extreme' (BF < 0.01) evidence in support of the null hypothesis, respectively. Within-condition analyses revealed small-to-medium hypertrophic adaptation in both conditions, with absolute increases ranging from 1.08 mm to 1.91 mm. These findings suggest that both knee flexion ROMs are similarly effective for promoting quadriceps femoris muscle hypertrophy over a relatively short training-period in resistance-trained individuals.

Keywords: Muscle length; knee extensors; regional hypertrophy; resistance training; ultrasonography.