Background and Aim: The normal response of H-reflex depression (HD) was reduced in chronic spinal cord injury (SCI) patients. The reduction of this normal response can lead to increase the muscle tone and spasticity. The purpose of this study is to investigate the effect of tripolar cathodal stimulation on HD in SCI patients.

Materials and Methods: This study was conducted in 10 volunteered SCI patients and 13 healthy male and female aged 28.91 ± 5.78 years. H-reflexes were elicited at 0.2, 5 and 0.2 Hz and intensity of 65-70 percent of the maximum H-reflex amplitude, before and after tripolar cathodal electrical stimulation of the spinal cord at T₁₁ level.

Results : Before trioplar stimulation, H-reflex amplitude decreased with increasing stimulation frequency only in healthy group. H-reflex amplitude decreased from 2.60 ± 1.48 to 1.34 ± 1.30 by 5Hz frequency (P=0.000). After trioplar stimulation in SCI patients group, HD increased with increasing stimulation frequency and H-reflex amplitude decreased significantly from 2.21 ± 1.98 by 0.2 Hz frequency to 1.29 ± 1.50 by 5Hz frequency(P=0.014).

Conclusion: Application of one session of cathodal trioplar stimulation can result the returning of normal HD in SCI patients. Cathodal trioplar stimulation is a non-invasive, without side effects, and an inexpensive method that may be a valuable tool to return the normal inhibition and modulating behavior of the spinal cord circuits.

Keywords: Spinal cord injury , Tripolar stimulation, H-reflex depression, Soleus muscle