Workouts, exercise and protein synthesis

Protein synthesis is initiated when a signal (e.g., nutrient, hormone, mechanical) to the cell is communicated to the DNA to induce gene expression (transcription), resulting in formation of messenger RNA (mRNA). The mRNA is translated into a protein through the process of translation by the ribosomes, which are free in the cytosol or bound to rough endoplasmic reticulum. The process of translation requiresa second form of RNA, called transfer RNA, and three distinct steps: initiation, elongation, and termination. Following translation, the nascent protein can be further modified through processes such as glycosylation or degradation (posttranslational modification). When the entire process of muscle protein synthesis is considered, there is ample evidence that this increases in a similar manner after both endurance and resistance exercise. Factors such as the intensity and duration of exercise also have profound effects on gene expression.

The sites of regulation and how this generalized protein synthetic response is fine-tuned to allow for phenotypical divergence are just becoming unravelled. We have used microarray technology and found that over 200 mRNA species are differentially expressed by only 3 h after endurance exercise, and only a minority of these same species are expressed in a similar fashion following resistance exercise. Others have found that phosphorylation of proteins such as p70S6k, 4E-BP1, eIF-2B, and AMPK is altered in response to different contraction patterns in skeletal muscle.

Collectively, the data show that there are changes at multiple levels (e.g., transcription and translation) within the protein synthetic pathway that simultaneously respond to exercise. It is also likely that the state of training will have a major role in determining the absolute and relative importance of transcriptional and translational control of certain proteins and how this relates to protein synthesis, ultimately modulating the phenotypic response to a given pattern of muscle contraction. Innovative approaches have revealed that muscle conserves the ability to acutely and directionally respond to divergent stimulii, even if its training history is at the opposite end of the metabolic demand spectrum.