Elevated muscle mass accompanied by transcriptional and nuclear alterations several months following cessation of resistance-type training in rats

Rodent studies investigating long-term effects following termination of hypertrophy-inducing loading have predominantly involved exposures such as synergist ablation and weighted wheel running or ladder climbing. This research yielded a spectrum of results regarding the extent of detraining in terms of muscle mass and myonuclei number. The studies were also limited in their lack of sensitive performance measures and indirect relatedness to resistance training. Our research group developed and validated a relevant rat model of resistance-type training that induces increased muscle mass and performance. The aim of the present study was to determine to what extent these features persist 3 months following the termination of this training. While performance returned to baseline, muscle mass remained elevated by 17% and a shift in distribution to larger muscle fibers persisted. A 16% greater total RNA and heightened mRNA levels of ribosomal protein S6 kinases implicated preserved transcriptional output and ribosomal content. Remodeling of muscle fiber nuclei was consistent with these findings - increased nuclear number and a distribution shift to a more circular nuclear shape. These findings indicate that muscle mass detrains at a slower rate than performance and implicates multiple forms of myonuclear remodeling in muscle memory.

Automated summary

Rodent studies have shown that the detraining effect on muscle mass varies after termination of hypertrophy-inducing loading. However, these studies have limitations in terms of sensitive performance measures and indirect relatedness to resistance training. Our research group developed a relevant rat model of resistance-type training and found that muscle mass remains increased three months after termination, indicating a slower detraining rate than performance. Multiple forms of myonuclear remodeling were implicated in muscle memory.