Skeletal muscles are covered by fascia that extends beyond their ends as tendons. Muscles are frequently grouped as synergists and antagonists. The muscle that works hardest is the prime mover.
Skeletal muscles maintain posture, cause movement, and produce heat.
Skeletal muscles are named according to their size, shape, location, direction of fibers, number of attachments, or action. The plasma membrane of a muscle fiber is its sarcolemma. Its endoplasmic reticulum is called the sarcoplasmic reticulum, which stores calcium. The sarcolemma invaginates into T tubules that contact the sarcophasmic reticulum. Myofibrils are cylindrical structures within muscle fibers.