At birth, there joints were covered by a tough, flexible, layer of tissue. By age 17, the bones of the skull have grown together so tightly that no movement in the joints is possible. Muscles are needed to move your limbs. Muscles also mix your food and move blood throughout your body. The form and size of the bones give the body shape.
Work is the result of a force moving an object through a distance.
Muscles are always partially contracted- this is known as muscle tone . Thus, muscles are always ready to do mork.