Methods of tendon jerk reinforcement. The role of muscle activity in reflex excitability.

This study was designed to reconcile the following clinical observations: subjects with anxiety repre- sented in muscle tension generally have hyperactive tendon jerks. Yet, muscle tension evidenced by in- complete relaxation frequently results in reflex depression and the tendon reflex can only be elicited by having the subject 'relax'. Under con- sideration were the observations by Hoffmann (1922) and by Hagbarth (1962) that a moderate amount of voluntary activity facilitates the monosynaptic reflex in the muscle tested. A problem to be investigated was the relationship of the facilitation produced by the Jendrassik manoeuvre, during forceful contraction of distant muscles masses, to that produced by voluntary activity in the same muscle. Numerous other techniques have been reported to be useful in facilitating reflexes, ostensibly through an effect on muscle activity. Cutaneous stimuli, such as needleprick, cold or warm baths, pinching, electrical shock, or manipulation of muscles have been variously reported to reinforce the tendon jerks. It has been suggested that the effectiveness of these manoeuvres is related to the distraction of attention, assisting the relaxation of muscles held in high tension