Gymnastik- och idrottshögskolan, GIH

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 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. 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 post-intervention 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.