The intermittent contraction of a muscle in normal or resting state is called muscle tension or tonicity. Muscles are attached to bones by tendons. Each organ requires two types of muscles to move. These two muscles together are called antagonistic muscles. During limb movement, one muscle contracts and the other muscle stretches. That is, when one muscle is shortened, the opposite muscle is lengthened. Two types of muscles are attached to the humerus of the arm. Biceps muscle and triceps muscle. The biceps muscle contracts and the triceps muscle stretches when the arms are raised. At this time, no shock is felt in the muscles. Again, the biceps muscle is stretched and the triceps muscle is contracted as the arm is lowered. At this time, the muscles do not feel any pressure. Only the muscles are tense.
Muscle contains actin and myosin proteins. These proteins extend from one end of the muscle to the other and can stretch the muscle. This means that the muscles are only stretched, but not pushed.