Effects of Range of Motion on Skeletal Muscle Hypertrophy and Molecular Adaptations in Resistance-Trained Men

Abstract

This study examined how lengthened partial (LP) versus full range of motion (FULL) lower-body resistance training affects acute post-exercise signaling and chronic hypertrophy and cellular adaptations of the vastus lateralis (VL) muscle in resistance- trained men. Eight men (22±1 years old, 5.6±1.4 years training experience) completed a crossover study whereby VL biopsies were collected pre-exercise and 0, 3, and 24 hours following LP and FULL leg extension bouts for transcriptomic and anabolic signaling analyses (Experiment 1). Another 16 men (26±5 years old; 8.0 ± 4.9 years training experience) completed an 8-week, twice-weekly lower-body intervention using a within- subject contralateral limb design (Experiment 2). One leg was randomly assigned to FULL and the contralateral leg to LP training across three exercises (leg press, leg extension, and lying leg curl). Pre- and post-intervention outcomes included VL muscle cross-sectional area (mCSA) summed across five equidistant MRI-derived transverse and mid-thigh biopsy outcomes. Condition × Time interactions for all outcomes were assessed using linear mixed-effects models. In Experiment 1, both conditions produced similar time-dependent changes in the VL transcriptome and anabolic signaling, but minimal between-protocol interactions. In Experiment 2, VL summed mCSA significantly increased over time (mean change: 9.3 cm², 95% CI [6.8, 11.8], P<0.001), but there was no clear evidence of differential change between LP and FULL (LP − FULL change: −1.4 cm², 95% CI [−6.1, 3.4], P = 0.640). Additionally, no significant interactions existed for type I fiber CSA (P=0.476), type II fiber CSA (P=0.350), type I fiber myonuclei (P=0.813), type II fiber myonuclei (P=0.589), type I and II satellite cell number (P=0.102 and P=0.797, respectively), or total RNA content (P=0.537). In conclusion, these data suggest that LP and FULL resistance training when executed within a typical lower body program broadly elicit similar acute and chronic VL responses in previously trained men.