Dynamic time course of muscle proteome adaptation to programmed resistance training in rats

Resistance training promotes muscle protein accretion and myofiber hypertrophy, driven by dynamic processes of protein synthesis and degradation. Muscle adaptations to ongoing resistance training occur over weeks, but most molecular knowledge on the process of adaptation is derived from static measurements at specific time points, which do not capture the dynamics of the adaptation process. To address this, we utilized deuterium oxide labeling and peptide mass spectrometry to quantify absolute protein content (grams) and synthesis rates (grams/day) in skeletal muscle during a time series experimental design. A daily programmed resistance training regimen was applied to male rat tibialis anterior via electrical stimulation of the left hindlimb for 10, 20, and 30 days (5 sets of 10 repetitions daily). Muscle samples from stimulated and contralateral control limbs were analyzed, quantifying 658 protein abundances and 215 protein synthesis rates. Unsupervised temporal clustering of protein responses revealed distinct phases of muscle adaptation. The early (0-10 days) response was driven by greater rates of ribosomal protein accretion and the mid (10-20 days) response by expansion of mitochondrial networks. These findings highlight that subsets of proteins exhibit distinct adaptation timelines due to variations in translation and/or degradation rates. The new understanding of temporal patterns highlighted by our dynamic proteomic data helps interpret static data from studies at isolated time points and could improve the development of strategies for optimizing muscle growth and functional adaptation to resistance training.<b>NEW & NOTEWORTHY</b> We used stable isotope labeling and proteomic analyses to quantify absolute changes in the synthesis and abundance of muscle proteins during programmed resistance training in rat in vivo. This novel time-resolved approach revealed distinct phases of adaptation, characterized by early ribosomal and later mitochondrial protein accretion. Strikingly, we observed substantial "oversynthesis" of muscle proteins; that is, the net gain in muscle protein content was much less than the amount of newly synthesized protein.