Calcium is significant in muscle contraction as it facilitates the interaction between actin and myosin, two key proteins in muscle fibers. When a muscle is stimulated by a nerve impulse, calcium ions are released from the sarcoplasmic reticulum, triggering the contraction process. These ions bind to troponin, leading to a change in the structure of tropomyosin, exposing active sites on actin. This exposure allows myosin heads to attach, resulting in muscle shortening and contraction. Adequate calcium intake is essential for optimal muscle function and performance.