Comparable Strength and Hypertrophic Adaptations to Low-Load and High-Load Resistance Exercise Training in Trained Individuals: Many Roads Lead to Rome

Abstract

The muscular and myocellular adaptations to low-load resistance exercise training (LL-RET) remain incompletely understood, particularly in the trained state. The primary aim of this study was to examine adaptations to an LL-RET regimen and compare these to a high-load training regimen (HL-RET). Fourteen resistance-trained males and females (26.4 {+/-} 4.4 years) participated in a 9-week RET program (twice per week). Using a within-subject design, each individual trained one leg with HL-RET (3-5 repetitions), and the other with LL-RET (20-25 repetitions), all sets performed to volitional failure. Pre- and post-intervention, muscle endurance, maximal strength, and muscle thickness using ultrasound was assessed. Muscle biopsies were analyzed for fiber type composition, fiber cross-sectional area (fCSA), and satellite cell- and myonuclear content using immunofluorescence. The training regimens led to comparable increases in maximal strength in multi-joint movements (21%), but not in single-joint movements were HL-RET was superior. LL-RET induced superior improvements in local muscle endurance (9% vs -2.7%, p=0.013). Regardless of training regimen, muscle thickness increased by [~]7.4% at the mid-thigh site and [~]8.5% at the distal site pre-to post-intervention. However, no changes were observed in fiber type composition or fCSA. Satellite cell content increased by [~]25% in type I fibers, independent of training regimen, but no changes were noted in myonuclear content. Here we novelly show that LL-RET can replicate many aspects of HL-RET leading to similar increases in both muscle hypertrophy and strength. Our study thus supports the notion that comparable adaptations to RET can be achieved using distinct loading regimens. New and noteworthyThis study compared two distinct resistance exercise loading strategies (3-5 RM vs. 20-25 RM) in trained individuals, evaluating both muscular and myocellular adaptations. Our findings demonstrate that low-load resistance exercise training (LL-RET) is an effective alternative to traditional high-load strategies for increasing strength and muscle size. These results highlight that skeletal muscle growth can be achieved through various external stressors, offering valuable insights for individuals seeking hypertrophy but unable to tolerate high loads.