Muscle tone

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. 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. If 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 maintain balance. Such near-continuous innervation can be thought of as a 'default' or 'steady state' condition for muscles. Both the extensor and flexor muscles are involved in the maintenance of a constant tone while at rest. In skeletal muscles, this helps maintain a normal posture.