Tension is not created or destroyed. It's just moved/transferred.
In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle's resistance to passive stretch during resting state. It helps to maintain posture and declines during REM sleep
PurposeIf a sudden pull or stretch occurs, the body responds by automatically increasing the muscle's tension, a reflex which helps guard against danger as well as helping to maintain balance. Such near-continuous innervation can be thought of as a "default" or "steady state" condition for muscles. There is, for the most part, no actual "rest state" insofar as activation is concerned. Both the extensorand flexor muscles are involved in the maintenance of a constant tone while "at rest." In skeletal muscles, this helps maintain a normal posture.
Although cardiac muscle and smooth muscle are not directly connected to the skeleton, they also have tonus in the sense that although their contractions are not matched with those of antagonist muscles, the non-contractile state is characterized by (sometimes random) enervation.
During a contraction of a movement the tension within the muscle is creating a range of motion. Enough tension within a muscle can break down the muscle fibers. This is the premise of muscle hypertrophy.