Hypertrophy

Hypertrophy is an increase in the size of an organ or tissue due to enlargement of its cells, rather than an increase in cell number (the latter process is called hyperplasia). It can occur in many tissues, most notably skeletal muscle and the heart.

In skeletal muscle, hypertrophy is most commonly driven by resistance training or other mechanical stimuli. It involves increased synthesis of contractile proteins, expansion of myofibrils, and sometimes the addition of new sarcomeres within existing muscle fibers. Cellular signaling pathways linked to hypertrophy include the mechanistic target of rapamycin (mTOR) and growth factors such as IGF-1; myostatin acts as a negative regulator. Satellite cells may contribute by donating nuclei, supporting fiber growth and repair.

Types of hypertrophy are often distinguished by cause and outcome. Physiological hypertrophy arises from regular exercise and generally improves muscle function and endurance. Pathological hypertrophy is associated with disease states, such as chronic hypertension or valvular heart disease in the heart, and can become maladaptive, potentially leading to functional impairment and heart failure. In the cardiovascular system, the distinction between adaptive (athlete’s heart) and maladaptive remodeling is an important consideration.

Other tissues can undergo hypertrophy as well, though the mechanisms and consequences vary by tissue type. Clinically, hypertrophy is evaluated through imaging and, when needed, tissue analysis or functional assessment. Management focuses on addressing the underlying stimulus or disease process; in many cases, physiological hypertrophy is reversible if the triggering stimulus is removed or reduced.