Smooth muscle is found in the walls of hollow organs and tubes, such as the stomach and blood vessels. Cardiac muscle forms the walls of the heart. Muscle activation is controlled by the nervous system, hormones, and some factors within the muscles themselves. Bones and muscles become weakened from lack of use. Muscles will atrophy causing as then to be smaller and weaker.
Exercise stretches muscles placing tension on bones.
It is this tension that allows bones to remain strong. Lack of exercise or stress on bones causes bones to loose their minerals and therefore become brittle and easily broken. The skeleton serves several functions. Specific bones connected in a special way that allows for particular directional movements are called joints . The framework of bones allows for the support of weight with upright posture.