Tonic vibration reflex

Tonic vibration reflex is a sustained contraction of a muscle subjected to vibration. This reflex is caused by vibratory activation of muscle spindles — muscle receptors sensitive to stretch.

Tonic vibration reflex is evoked by placing a vibrator — which in this case is typically an electrical motor with an eccentric load on its shaft — on a muscle's tendon. 30–100 Hz vibration activates receptors of the skin, tendons and, most importantly, muscle spindles. Muscle spindle discharges are sent to the spinal cord through afferent nerve fibers, where they activate monosynaptic and polysynaptic reflex arcs, causing the muscle to contract.