Bundles of long fibers that shorten when a nerve signal releases calcium inside them. Muscle is also the body's largest site for storing glucose.
How it works, step by step
A nerve signal reaches the muscle fiber.
Calcium is released inside the fiber.
Myosin heads, powered by ATP, pull on actin filaments.
The fiber shortens; the tendon pulls the bone.
Building muscle
Resistance training is the main signal for muscle growth; adequate protein and energy support it.
Aging
Muscle mass and strength decline with age; strength training slows this at any age.
Evidence & sources
No single food 'feeds' a muscle directly. Evidence: established. Known: Muscle relies on overall energy, protein and electrolytes delivered through blood. Unknown: — Source: Body Unpacked editorial principle, Methodology — avoiding single-food claims (2026).