Air-splint pressure effect on soleus muscle alpha motoneuron reflex excitability in subjects with spinal cord injury

Objective: This study investigated circumferential pressure effect on soleus motoneuron reflex excitability in subjects with spinal cord injury (SCI). Setting: A university neuromuscular research laboratory. Subjects: Six men with SCI, clinical level above L1. Outcome Measures and Intervention: Soleus motoneuron reflex excitability was assessed by measuring the average change in the peak-to-peak amplitude of 10 H-reflexes before (baseline), during (1, 3, and 5 min) and after (1, 3, and Smin) pressure application. Pressure was applied to the lower leg by manually inflating an air-splint to a maintained range of 36.7 to 40.8mmHg for 5 minutes, after which it was deflated. Design: Repeated measures, planned comparison. Dependent variables compared with baseline values only in post hoc tests. Results: A one-way analysis of variance for repeated measures demonstrated significant difference (F-6.30=4.03; P=.004) in the H-reflex amplitude across test conditions, Post hoc t tests (with Bonferroni's correction for multiple comparisons, p less than or equal to.008) revealed a significant H-reflex amplitude reduction at 1, 3, and 5 minutes of pressure application when measurements were compared with the baseline value. Postpressure measurements returned to baseline; however, the third minute measurement was significantly greater than baseline values. Conclusions: Circumferential pressure applied to the lower leg decreased soleus muscle alpha motoneuron reflex excitability in subjects with SCI. This inhibition lasted only as long as the pressure was applied. Circumferential pressure application may be useful when a temporary decrease in muscle activity is a therapeutic goal in patients with SCI. (C) 1996 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.