Every time you move, your muscles contract and relax. This process only takes a few seconds, but it is actually a quite complex process. Every activity in our body is controlled by muscles: breathing, circulation of blood, digestion. Even a simple smile is a result of muscle action. Muscles also help keep our body warm, maintain posture, and stabilize bones and joints. The body contains several types of muscles, some that work involuntarily, such as heart and organ muscles, and skeletal muscles that work primarily through voluntary action that is controlled consciously.