Muscle Growth, Repair and Preservation: A Mechanistic Approach

Resistance exercise, amino acid ingestion and an anabolic hormone environment all have the capacity to elevate muscle protein synthesis (MPS), while a catabolic hormone environment, such as elevated pro-inflammatory cytokines as seen during disuse, aging, and conditions such as cancer and AIDS, can cause an increase in muscle protein degradation (MPD). When the rate of MPS exceeds that of MPD there is a positive net protein balance (NPB) and over a prolonged period of time this results in accretion of contractile material and muscle growth, or hypertrophy. In contrast, when NPB is chronically negative, muscle atrophy occurs, i.e. muscle size decreases. Various signaling pathways within the muscle fiber appear to play a crucial role in the adaptive processes, and understanding how these pathways can be modulated will help the design of therapies to prevent or reverse muscle atrophy in a host of muscle wasting conditions