This document discusses chemical changes that occur during skeletal muscle contraction. It explains that ATP is utilized to polymerize G-actin into F-actin and form actomyosin complexes between actin and myosin fibers. Over 95% of long-term energy for muscle contraction comes from oxidative phosphorylation. The nature of heat production during muscle contraction depends on whether it is isotonic or isometric. After death, no new ATP is produced, preventing actin and myosin from separating and causing muscles to remain contracted.