The Regulation of Human Skeletal Muscle Mass by Contractile Perturbation

Overview

It is well known that periods of weight training lead to increases in skeletal muscle size and strength. In contrast, periods of inactivity such as bed rest or immobilization result in losses of skeletal muscle size and strength. However, individuals experience variable magnitudes of muscle size change in response to changes in mechanical tension, such that certain individuals experience large changes in muscle mass whereas others do not. What is not currently known, and will be the primary goal of the present investigation, is to determine whether individuals who gain the most muscle mass with exercise training also lose the most muscle when they are immobilized. The investigators hypothesize that individuals who gain the most muscle with training will also lose the most with immobilization.

Resistance exercise, paired with protein ingestion, leads to the accretion of muscle proteins that over time results in the augmentation of muscle size and muscle strength. By virtue of its ability to stimulate increases in muscle size and strength, resistance exercise is an effective method that can be used by healthcare practitioners to promote the recovery of lost muscle mass resulting from a period of immobilization (resulting from broken bones, elective surgery, etc.). However, while exercise in general is an effective therapeutic strategy to combat muscle loss and frailty, the extent to which individuals respond to resistance exercise is highly variable. Some individuals exhibit large changes in muscle size (high responders) whereas other exhibit little to no change (low responders). Thus, where as one resistance exercise program might be an appropriate treatment for one individual following disuse, another individual might require a greater stimulus and/or pharmaceutical assistance in order to fully recover. What is currently unknown is whether individuals who experience the most profound increases in skeletal muscle mass following resistance exercise also lose the most muscle upon limb immobilization. Answering this gap in our knowledge will be the primary goal of this study. The procurement of this knowledge will hopefully permit the development of individualized exercise programs that can be used to influence the recovery of skeletal muscle that is lost with inactivity and immobilization.