Effect of Exercise on the Human Skeletal Muscle Phosphoproteome

Skeletal muscle is a highly plastic tissue, capable of adapting to changes in nutritional intake and contractile activity. For instance, resistance exercise results in a mild stimulation of rates of muscle protein breakdown (MPB) but a greater stimulation of the rates of muscle protein synthesis (MPS). When resistance exercise is performed prior to protein ingestion there is a synergistic combination of the two stimuli such that rates of MPS are stimulated over and above those of MPB. Thus, repeated bouts of resistance exercise, when coupled with protein ingestion, result in the accretion of skeletal muscle protein referred to as hypertrophy. Importantly, by changing the nature of the exercise stimulus, it is possible to redirect the focus of the type of skeletal muscle proteins that are being synthesized. For example, prolonged and repeated lower-load dynamic stimulation of skeletal muscle (i.e., endurance exercise training) results in an increase in the expression of mitochondrial genes, proteins, and ultimately enhanced mitochondrial content, leading to a shift towards an oxidative phenotype, and improved fatigue resistance. Resistance exercise training also stimulates the transcription of genes and accrual of new muscle proteins, but these genes and proteins are largely associated with the myofibrillar protein fraction, and regular resistance exercise leads to muscle hypertrophy and increased force-generating capacity. However, during the early stages of exercise training, particularly in training-naïve participants there is a significant increase in the expression of genes common to both modalities of exercise. It is only with sustained exercise training that there is a 'fine-tuning' of the transcriptome, the protein synthetic response, and then the proteome that gives rise to divergent hypertrophic and oxidative phenotypes.