Objective: To determine the construct validity of Myotonometer measurements of tissue compliance as being reflective of ankle plantarflexor tone.
Design: Cross sectional.
Setting: Motor performance research laboratory.
Participants: Twenty-three stroke survivors (67.5+/-10.9y) and 24 control subjects (71.2+/-9.0y) recruited from the community.
Interventions: Not applicable. Main outcome measures Plantarflexor tone was measured using the Modified Ashworth Scale (MAS), ankle stiffness (total, passive, intrinsic and reflex components) was quantified using a torque motor, and tissue compliance during relaxation and activation of the plantarflexors was measured with the Myotonometer.
Results: MAS scores in the stroke group ranged from 1 to 4, whereas all control subjects had normal tone. Mean total ankle stiffness was higher in the stroke group than in the control group (P<.02), mainly due to elevated passive stiffness (P<.03). Compliance did not change as a function of muscle activation in stroke, but it decreased when control subjects contracted their plantarflexors (P<.04). The difference in Myotonometer measurements acquired during active and relaxed states was associated with total ankle stiffness and, specifically, intrinsic stiffness. The relationships were strongest when only stroke data were considered.
Conclusions: Stiffness and compliance measures distinguished between control subjects and persons with hypertonia secondary to stroke. Compliance differences in the relaxed and active gastrocnemius muscle reflected intrinsic stiffness associated with the contractile elements of the plantarflexor group of muscles as a whole.