Effects of Continuous and Pulsed Ultrasound on the Parameters of Hoffmann's Reflex

In this study the effects of continuous and pulsed ultrasound (3 MHz) on the parameters of hoffmann's reflex (H reflex) were compared with each other. In order to do this, 14 healthy female subjects aged between 25 and 35 years old (mean = 26.64, SD = 2.71) were tested. Ultrasound (U.S) was applied on the sciatic nerve of right lower limbs on the posterior aspect ofthe thighs at two different sessions. The area oftreatment was 20 square em (2*10). Duration ofthe treatment was 5 minutes and the intensity ofthe U.S. was 1 watt per square em, The duty cycle was 10% for the pulsed ultrasound. -,Parameters ofM wave and H reflex of the soleus muscle (amplitudes of Y2 Hmax, duration and latency) were measured and recorded before the application ofthe U.S. (TO) and immediately (TI), 5 minutes (T5), 10 minutes (TIO) and 15 minutes (TI5) after the U.S. Statistical analysis of the data (ANOVA repeated measurement and paired t-test) showed that the continuous ultrasound increases the amplitude ofH-reflex significantly (P < 0.01). There was no significant difference in the latency before and after the application of U.S.These results may' be due to thermal effects of continuous U.S. on the reflex arc and it seems that the continuous U.S. (3 MHz) increases the excitability ofthe alpha motoneurone.