Muscle biology is the scientific study of how muscles develop, function, and support the body's overall health. At the cellular level, muscles are composed of specialised fibres that contract and relax, generating force and enabling movement. The body has over 600 muscles, and they are classified into three primary types: skeletal, smooth, and cardiac muscles. Each plays a unique role in movement, circulation, digestion, and posture.

Skeletal muscles are under voluntary control and are attached to bones. These muscles facilitate walking, lifting, sitting upright, and other physical activities. They account for nearly 40% of total body mass and contain highly organised protein structures called sarcomeres. Sarcomeres house actin and myosin filaments, the key proteins responsible for muscle contraction.

Smooth muscles function involuntarily and are found in the walls of internal organs like the intestines, blood vessels, and bladder. They help regulate functions such as digestion, blood pressure, and urinary flow.

Cardiac muscle, found only in the heart, is striated like skeletal muscle but functions involuntarily. It contains specialised junctions called intercalated discs, which help synchronise contractions for effective blood pumping.

The neuromuscular system is central to muscle control. It involves the transmission of electrical signals from the brain to muscles via motor neurons. At the neuromuscular junction, these signals release the neurotransmitter acetylcholine, initiating a cascade that causes calcium release and subsequent muscle contraction.

Muscle contraction follows the sliding filament model, where actin and myosin slide past one another to shorten the muscle fibre. This process requires ATP (adenosine triphosphate) as energy. Relaxation occurs when calcium ions are reabsorbed, halting the interaction between filaments.