Low responders to endurance training exhibit greater atrophy

Divergent skeletal muscle phenotypes result from chronic resistance-type versus endurance-type contraction, reflecting the principle of training specificity. However, it is unclear whether there is a common set of genetic factors that influence skeletal muscle adaptation to disuse. Female rats were obtained from out-bred lines selectively bred from high responders to endurance training (HRT) or low responders to endurance training (LRT; n=6/group; generation 19). Both groups underwent 3 d of hindlimb immobilization to induce atrophy of the plantaris and soleus muscles prior to comparison to non-immobilization controls of the same genotype. RNA sequencing was performed to identify Gene Ontology Biological Processes with differential (LRT vs HRT) gene set enrichment. Running distance, determined well in advance of hindlimb immobilization, increased in response to aerobic training in HRT but not LRT. The atrophy response to hindlimb immobilization was exaggerated in LRT versus HRT. There were between-group differences for 140 processes in plantaris muscle and 118 processes in soleus muscle. In conclusion, low responders to aerobic endurance training exhibited exaggerated atrophy, and this was associated with differential gene expression. Thus, our findings suggest that genetic factors that underpin aerobic training maladaptation may also dysregulate the transcriptional activity of biological processes that contribute to adaptation to hindlimb immobilization. RNA-seq of 14-month old female LRT/HRT rats (generation 19) following 3 days atrophy of plantaris and soleus compared to controls (total=24 samples; n=6/group)