This document discusses the three main types of muscles in the human body: skeletal, smooth, and cardiac muscles. Skeletal muscles are voluntary muscles that are attached to bones by tendons and allow for movement of the body. Smooth muscles are involuntary and control internal organs. Cardiac muscle is only found in the heart and contracts involuntarily around 70 times per minute each day. The document explains how muscles contract to create movement and require energy from glucose to function properly.