H-reflex modulation during gait in multiple sclerosis patients with spasticity.

The aim of the present study was to quantitate the Hoffmann (H-) reflex modulation in the soleus muscle of spastic multiple sclerosis patients during walking at different stimulus strengths, and to quantitate the influence of the excitation level of the soleus muscle on the H-reflex. The H-reflex modulation was quantified by the minimum H-reflex in the swing phase and the modulation index introduced by Yang et al. (1). Stimulus strengths were matched between subjects, and only stimuli intensities, which reflect modulation in the H-reflex with true neurophysiological origin, were used. Based on this approach, we found that the reflex modulation is impaired in moderate spastic patients at both a strong and a weak afferent input to the motoneuron pool in consistency with studies on severe spastic patients. This study concludes that the H-reflex modulation in the spastic patients is only related to the excitation level of the muscles, whereas both the excitation level and other factors than the excitation level are known to influence the H-reflex modulation in healthy subjects.