Adaptive time course of the skeletal muscle proteome during programmed resistance training in rats

Resistance training (RT) promotes muscle protein accretion and myofiber hypertrophy, driven by dynamic processes of protein synthesis and degradation. While molecular studies have focused on acute signalling or long-term hypertrophy and strength gains, a critical gap remains in understanding the intermediate processes of muscle adaptation. Acute signalling does not always correlate directly with long-term outcomes, highlighting the need for a time-course analysis of protein abundance and turnover rates. To address this, we utilised deuterium oxide labelling and peptide mass spectrometry to quantify absolute protein content and synthesis rates in skeletal muscle. A daily programmed resistance training regimen was applied to the rat tibialis anterior (TA) via electrical stimulation of the left hind limb for 10, 20, and 30 days (5 sets of 10 repetitions daily). Muscle samples from stimulated (Stim) and contralateral control (Ctrl) limbs were analysed, quantifying 658 protein abundances and 215 protein synthesis rates. Unsupervised temporal clustering of protein responses revealed distinct phases of muscle adaptation, with early (0-10 days) and mid (10-20 days) responses driven by differential protein accretion rates in ribosomal and mitochondrial networks, respectively. These findings suggest that subsets of proteins exhibit distinct adaptation timelines due to variations in translation and/or degradation rates. A deeper understanding of these temporal shifts could improve strategies for optimising muscle growth and functional adaptation to resistance training.