Tone-Inhibiting Insoles Enhance the Reciprocal Inhibition of Ankle Plantarflexors of Subjects With Hemiparesis After Stroke: An Electromyographic Study

Abstract

BackgroundSpasticity is a common sequela of upper motor neuron pathology, such as cerebrovascular diseases and cerebral palsy. Intervention for spasticity of the ankle plantarflexors in physical therapy may include tone-inhibiting casting and/or orthoses for the ankle and foot. However, the physiological mechanism of tone reduction by such orthoses remains unclarified. ObjectiveTo investigate the electrophysiologic effects of tone-inhibiting insoles in stroke subjects with hemiparesis by measuring changes in reciprocal Ia inhibition (RI) in the ankle plantarflexor. DesignAn interventional before–after study. SettingAcute stroke unit or ambulatory rehabilitation clinic of a university hospital in Japan. ParticipantsTen subjects (47-84 years) with hemiparesis and 10 healthy male control subjects (31-59 years) were recruited. MethodsRI of the spastic soleus in response to the electrical stimulation of the deep peroneal nerve was evaluated by stimulus-locked averaging of rectified electromyography (EMG) of the soleus while subjects were standing. Main Outcome MeasurementsThe magnitude of RI, defined as the ratio of the lowest to the baseline amplitude of the rectified EMG at approximately 40 milliseconds after stimulation, was measured while subjects were standing with and without the tone-inhibiting insole on the hemiparesis side. ResultsEnhancement of EMG reduction with the tone-inhibiting insole was significant (P < .05) in the subjects with hemiparesis, whereas no significant changes were found in controls. ConclusionTone-inhibiting insoles enhanced RI of the soleus in subjects after stroke, which might enhance standing stability by reducing unfavorable ankle plantarflexion tone. Level of EvidenceIII