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

Loading-induced hypertrophy with transcriptional upregulation has been observed concomitant with nuclei accretion in various studies regarding both humans and rodents. Bruusgaard et al. in 2010 pioneered work utilizing a model of synergist ablation to cause hypertrophy followed by denervation-induced atrophy to demonstrate that load-induced gains in myonuclei could be long-lasting after the termination of such exposure. This finding was consistent with the idea of enduring myonuclear accretion as a form of “muscle memory” allowing enhanced muscle adaptation following a period of detraining. Subsequent research groups further investigated this possibility in the context of exercise utilizing rodents and various loaded exercise paradigms such as weighted wheel running and ladder climbing. This research yielded a spectrum of results. While these studies were instrumental in highlighting the variation in outcomes possible following load-induced hypertrophy in general, they were limited in their direct relatedness to resistance training – the predominate form of exposure utilized to induce hypertrophy. Our research group has established and repeatedly validated a rat research model to investigate resistance-type training. The model is based on using a dynamometer to precisely expose dorsiflexor muscles of rats to 8 sets of 10 repetitions (per set) of stretch-shortening contractions (SSCs) – a consecutive sequence of isometric, lengthening, and shortening contractions. Training with this exposure 3 sessions per week for one month results in increases in muscle mass and performance. This is accompanied by an increase in muscle fiber area accompanied by a proportional increase in myonuclei number and a rise in overall transcriptional output as measured by total RNA levels. The purpose of the present study was to determine to what extent alterations in performance, muscle mass, nuclei number, and transcriptional output persist several months following the termination of this relevant and valid model of resistance-type training.