Muscles

Muscles are specialized tissues that contract and relax to produce movement, maintain posture and generate heat. The human body contains more than 600 muscles, accounting for about 40% of an adult's body weight on average. There are three main types of muscle. Skeletal muscles are attached to bones by tendons and allow voluntary movements such as walking, writing and lifting objects.

Smooth muscles are found in the walls of organs and blood vessels, where they move food through the digestive tract and help regulate blood flow without conscious control. Cardiac muscle forms the heart and contracts continuously throughout life to pump blood around the body. Muscle cells obtain the energy they need from nutrients and oxygen delivered by the bloodstream.

Most movements result from muscles working together in coordinated groups, with some contracting while others relax. Besides producing movement, muscles stabilize joints, protect certain organs and help maintain body temperature because their activity releases heat. Regular physical activity strengthens muscles, improves endurance and helps preserve flexibility and balance.

Adequate protein intake, a varied diet and sufficient recovery also support healthy muscle function. As people age or remain inactive for long periods, muscle mass and strength can gradually decrease, although regular exercise can slow this process. Doctors evaluate muscle health through physical examination and, when necessary, tests such as imaging, electrical studies or measurements of muscle strength.