Input-output properties of the soleus stretch reflex in spastic stroke patients and healthy subjects during walking

The input-output properties of the soleus stretch reflex during walking and sitting were examined in 11 spastic stroke patients and 10 healthy subjects. In the early swing phase, the threshold of the input-output relation was significantly lower in the patient group - on average 108 degrees/s compared to 309 degrees/s in the control group (P = 0.02). The slope of the input-output properties was unchanged in patients and in control subjects (P = 0.39). In stroke patients we found a minor, but significant, difference in threshold with 108 degrees/s in the early swing phase compared to 74 degrees/s in sitting position at matched TA EMG activity (P = 0.01), Furthermore, we found an unchanged slope of 0.25 mu V s/degrees during walking and 0.28 mu V s/degrees in the sitting position (P = 0.21). In contrast, control subjects showed a large difference in the threshold in the early swing phase during walking (309 degrees/s) compared with findings in the sitting position at a matched TA EMG activity (71 degrees/s, P = 0.004). The slope was unchanged during walking and when the subject was sitting (P = 0.22). There was a significant correlation between clinical spasticity score and stretch reflex threshold in the early swing phase (P = -0.61, P = 0.04) and between clinical spasticity score and the slope in the early swing phase (P = 0.72, P = 0.009). It is concluded that in the early swing phase, the markedly reduced soleus stretch reflex threshold was preventing the stroke patients from making fast dorsiflexion of the foot at the ankle joint and thereby impairing the walking speed. (C) 1998 Elsevier Science Ireland Ltd.