Divergent strength gains but similar hypertrophy after low-load and high-load resistance exercise training in trained individuals: many roads lead to Rome

The muscular and myocellular adaptations to low-load resistance exercise training (LL-RET) remain incompletely understood in the trained state. The primary aim of this study was to examine adaptations to an LL-RET regimen, comparing these to a high-load training regimen (HL-RET). Fourteen resistance-trained males and females (26.4 ± 4.4 yr) participated in a 9-wk 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. Maximal strength (1 RM) and muscle thickness were 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 1 RM in multi-joint movements (21 ± 10%), but not in single-joint movements, where HL-RET was superior (9 ± 13% vs. -3 ± 10%). Regardless of training regimen, muscle thickness increased pre- to postintervention by 7 ± 17% at the mid-thigh site and 8 ± 8% at the distal site. However, this was not accompanied by changes at the myocellular level, with no observed differences in fCSA and fiber type composition. Satellite cell content increased by 25 ± 57% in type I fibers, independent of training regimen, but no changes were noted in myonuclear content. LL-RET can replicate many aspects of HL-RET, leading to similar increases in muscle hypertrophy and strength. Our study supports the notion that comparable adaptations to RET can be achieved using widely distinct loading regimens.<b>NEW & NOTEWORTHY</b> This 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 loads, offering valuable insights for individuals seeking hypertrophy but unable to tolerate high loads.