H-reflexes are less depressed following muscle stretch in spastic spinal cord injured patients than in healthy subjects.

The size of the soleus H-reflex was measured after a slow (17 deg/s) passive stretch of ankle plantarflexors and compared to its control size without muscle stretch in ten neurologically healthy subjects and in six spastic spinal-cord-injured patients. Two seconds after the end of the stretch, the size of the H-reflex was reduced to about 30% of its pre-stretch size in the healthy subjects. The depression remained for 10-15 s. In the spastic, spinal-cord-injured patients, stretch caused significantly less reduction in the size of the H-reflex. The H-reflex also regained its pre-stretch size much faster than in healthy subjects. We suggest that the smaller depression of the H-reflex observed in spastic patients may be involved in the pathophysiology of spasticity.