부산대학교 도서관

The stability of the maximal muscle response ([M.sub.max]) is critical to H reflex methodology. It has previously been reported that the amplitude of [M.sub.max] declines over time. If reproducible, this finding would have implications for all experimental studies that normalise the output of the motoneurone pool against the M wave. We investigated the effect of time on changes in [M.sub.max] and the maximal H reflex ([H.sub.max]) evoked at 4-s intervals over 60 min. To identify an influence of homosynaptic depression, we extended the interstimulus interval to 10 s and the time to 100 min. Two recording montages over soleus were used to ensure that interelectrode distance was not a critical factor. The soleus [M.sub.max] and H reflex were evoked by stimulation of the tibial nerve in the popliteal fossa in 7 subjects who sat with the knee flexed to 30° and the ankle plantar flexed by ~30°. We found no change in the pooled data for [M.sub.max],[H.sub.max], a reflex 50% of maximal, or the current required to produce it. However, one subject had a statistically significant increase in [M.sub.max] and a concurrent decrease in [H.sub.max] regardless of the interstimulus interval. On average, there was no change in the [H.sub.max]/[M.sub.max] ratio over time. While both [M.sub.max] and [H.sub.max] may change in response to many factors, these results suggest that, typically, time is not one of them. Keywords Maximal muscle response * H reflex * Spinal circuitry excitability * Human soleus muscle * Motor control
Introduction The H reflex is often used as a tool to probe the excitability of spinal circuitry and its role in human motor control (for reviews see Pierrot-Deseilligny and Mazevet [...]