- Skeletal muscle hypertrophy is a beneficial adaptation for many individuals. The metabolic basis for muscle hypertrophy is the balance between the rates of muscle protein synthesis (MPS) and muscle protein breakdown (MPB), i.e. net muscle protein balance (NMPB = MPS - MPB). Resistance exercise potentiates the response of muscle to protein ingestion for up to 24 h following the exercise bout. Ingestion of many protein sources in temporal proximity (immediately before and at least within 24 h after) to resistance exercise increases MPS resulting in positive NMPB. Moreover, it seems that not all protein sources are equal in their capacity to stimulate MPS. Studies suggest that ∼20-25 g of a high-quality protein maximizes the response of MPS following resistance exercise, at least in young, resistance-trained males. However, more protein may be required to maximize the response of MPS with less than optimal protein sources and/or with older individuals. Ingestion of carbohydrate with protein does not seem to increase the response of MPS following exercise. The response of inactive muscle to protein ingestion is impaired. Ingestion of a high-quality protein within close temporal proximity of exercise is recommended to maximize the potential for muscle growth.