Muscle tone or residual muscle tension refers to the continuous and passive partial contraction of the muscles or their resistance to passive stretch during a resting state. In other words, when we are in a relaxed state our muscles maintain a bit of contraction in them which gives them a “springy” feel.
Unconscious nerve impulses maintain the muscles in a partially contracted state. 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 to maintain balance. Such near-continuous innervation is a default condition for muscles. Both the extensor and flexor muscles are involved in the maintenance of a constant tone while at rest. This helps maintain an upright posture.
Hypotonia or low muscle tone are shown as muscle flaccidity; where the limbs appear floppy, stretch reflex responses are decreased, and the limb’s resistance to passive movement is compromised.
Hypertonia or high muscle tone can present as either spasticity or rigidity. These cause resistance to movement in a variety of ways.