Muscle hypertrophy

Muscle hypertrophy is an increase in the size of muscle fibers, commonly produced by repeated resistance training. It increases muscle cross-sectional area without creating proportional increases in fiber number.

Mechanical tension: The force experienced by muscle fibers as they contract or resist being stretched. Resistance training creates tension that initiates many of the signals associated with fiber growth.
Skeletal muscle: Striated muscle attached to the skeleton that produces voluntary movement. Hypertrophy is most often discussed as growth in this muscle tissue.
Resistance training: Exercise that challenges muscles against external resistance to develop strength, endurance, or size. It is the most common deliberate stimulus used to increase muscle size.
Muscle hyperplasia: An increase in the number of cells in a tissue. It differs from hypertrophy, which enlarges existing fibers rather than increasing fiber number.
Mechanotransduction: The conversion of physical forces into biochemical signals within cells. It links loading of muscle fibers to intracellular pathways that regulate protein synthesis.
Muscle fiber: A long, multinucleated muscle cell that contracts to produce force. The defining structural change in hypertrophy is enlargement of individual fibers.
Repetition maximum: The greatest load that can be lifted for a specified number of repetitions. It provides a way to prescribe and compare resistance-training loads.
Muscle atrophy: A reduction in muscle size caused by loss of muscle protein and tissue. Atrophy is the opposing change in fiber size, often following disuse or disease.
Muscle protein synthesis: The cellular process of assembling amino acids into proteins in skeletal muscle. Hypertrophy occurs when muscle protein synthesis exceeds muscle protein breakdown over time.
Myofibril: A rod-like structure inside a muscle fiber, composed of repeating contractile units. Myofibrillar growth adds contractile machinery within hypertrophying fibers.

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