THE STRETCH REFLEX RESPONSE IN THE NORMAL AND SPASTIC ANKLE - EFFECT OF ANKLE POSITION

Objective: The influence of stretch of the gastrocnemiussoleus muscle on the stretch reflex activity was studied, by varying the ankle angle in steps from 10 degrees of plantarflexion (PF) to 5 degrees of dorsi flexion (DF). Design: Nonrandomized control trial. Setting: Department of Rehabilitation Medicine of a university medical center.Patients: S ixteen subjects with and 16 subjects without spasticity. Main Outcome Measures: The passive elastic stiffness and active reflex response, ex pressed by the total and elastic path lengths, were determined at each ankle angle as a sinusoidal displacement of 5 degrees was applied to the joint at frequencies from 3 to 12Hz. Results: The elastic stiffnes s showed no difference between the spastic and normal subjects for all ankle angles (p >.05). The elastic stiffness increased linearly simil arly in both groups when the ankle was dorsiflexed. The reflex respons e was sig nificantly greater in the spastic group for all positions (p less than or equal to .01). The total and elastic path lengths showed a linear increase in both groups when the ankle angle was varied from PF to DF. The spastic group, however, had a significantly faster incr ease (p less than or equal to .005). Between-group comparison showed a significant quadratic trend in the elastic path length for the spasti c group (p less than or equal to .05), with a maximum at 2.5 degrees o f DF. Conclusions: This study showed that the stretch reflex activity varies with the ankle position. This must be considered when performin g spasticity tests subsequent to an intervention that has changed the available range of motion and when comparing subjects measured at diff erent ankle positions. (C) 1996 by the American Congress of Rehabilita tion Medicine and the American Academy of Physical Medicine and Rehabi litation