Effect of tendon pressure on alpha motoneuron excitability.

The purpose of this study was to test the effect of tendon pressure on muscle activity by evaluating changes in the excitability of the motoneurons supplying the muscle. The excitability changes of the motoneurons were assessed by measuring changes in H-reflex amplitudes before, during, and after tendon-pressure application. Twenty-eight of 32 subjects with no known neurological deficit displayed an initial decrease in H-reflex amplitude during tendon pressure (mean = 60% of control values) but returned to 85 percent of control values within the first 5 seconds of pressure and reached 93 percent of control values within 30 seconds of application. The ANOVA revealed significant differences (p less than .05) and the post hoc t test showed these differences to be between control values and those obtained during the first 10 seconds of pressure. These findings support the clinical impression of reduced muscle tone resulting from tendon pressure. If these results are applied to a patient group, the transient behavior of the tendon-pressure response would limit the applicability of the technique to situations demanding an immediate, short-term reduction in muscle activity.