Lihasten

Lihasten is the Finnish term used to refer to the muscles, particularly the skeletal muscles that produce voluntary movement in humans and many other vertebrates. In Finnish medical and anatomical writing, lihasten encompasses the muscular system as a whole, though the everyday word lihas refers to a single muscle and lihasten to muscles in plural or as a collective.

Skeletal muscles are composed of muscle fibers organized into fascicles, surrounded by connective tissue. Each fiber contains myofibrils with sarcomeres—the contractile units made of actin and myosin. Contraction is triggered by calcium ions released from the sarcoplasmic reticulum in response to a nerve impulse at the neuromuscular junction. Energy is supplied by adenosine triphosphate (ATP) from various sources, including creatine phosphate, glycolysis, and oxidative phosphorylation.

Muscles provide movement, stabilize joints, maintain posture, and generate heat. They act in coordinated groups across the body, often as antagonistic pairs. Control is voluntary, via motor neurons that recruit motor units in a graded fashion depending on force and precision requirements. Blood vessels and nerves accompany muscles to provide nutrients and neural input, and the overall muscular system is integrated with the skeleton and circulatory system to support activity and endurance.

Muscle performance depends on fiber type composition, mitochondrial capacity, and training. Hypertrophy occurs with resistance exercise through increased sarcomeres and protein synthesis. Endurance training improves oxidative capacity and fatigue resistance. With aging, muscle mass declines—a process called sarcopenia—partly due to hormonal changes, reduced activity, and neural aging.

Common conditions affecting lihasten include muscular dystrophies, inflammatory myopathies, injuries, and age-related decline. Understanding muscle structure and metabolism supports medicine, sports science, and rehabilitation.