Acute Molecular and Chronic Vastus Lateralis Adaptations to Lengthened Partial versus Full Range of Motion Resistance Training in Trained Men

Purpose: This study examined how lower-body lengthened partial (LP) versus full range of motion (FULL) resistance training affects acute post-exercise signaling, chronic hypertrophy, and cellular adaptations of the vastus lateralis (VL) muscle in resistance-trained men. Methods: Eight males (22±1 years old, 5.6±1.4 years training) 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 males (26±5 years old; 8.0±4.9 years training) completed an 8-week, twice-weekly lower-body intervention using a within-subject design (Experiment 2). One leg was 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 MRI-derived slices and mid-thigh VL biopsy outcomes. Results: In Experiment 1, time-dependent changes in the VL transcriptome and anabolic (mTORC1 and Hippo) signaling occurred, but minimal between-protocol interactions existed. In Experiment 2, VL mCSA increased over time (mean change: 9.3cm², 95% CI [6.8, 11.8], P<0.001), with no evidence of differential change between protocols (LP−FULL change: −1.4cm², 95% CI [−6.1, 3.8], P=0.640). Additionally, no significant interactions existed for type I or II fiber CSA (P=0.476, P=0.350), type I or II fiber myonuclei (P=0.813, P=0.589), type I or II satellite cell number (P=0.102, P=0.797), or total RNA content (P=0.537). Conclusions: This exploratory study suggests that 8 weeks of LP and FULL resistance training elicit similar acute and chronic VL responses in previously trained men.