H-reflex and F-wave potentials in leg and arm muscles.

The systematic analyses of secondary muscle potentials of H-reflex and F-wave type were done in multicentric study. The examinations were carried out in healthy volunteers with 9 muscles analysed on the legs and 9 on the lower arms and hands. The H-reflex potential was found regularly in thigh muscles (vastus medialis 100%, biceps femoris 97%, semitendinosus 93%). Less frequently but still with high incidence it appeared in posterior lower leg muscles (soleus 93%, caput mediale gastrocnemii 73%). In anterior tibial muscle and extensor digitorum brevis it did not appear at all. Only exceptionally it was found in short peroneal muscle (3%) and occasionally, only on proximal nerve stimulation, in flexor hallucis brevis. The similar distribution pattern was found in lower arm and hand muscles with analysis on both sides. In flexor digitorum superficialis (73-70%) and flexor carpi radialis (73-57%) the percentage of H-potential muscles was the highest, in flexor carpi ulnaris (47-40%) lesser but still remarkable. Brachioradialis (37-30%) and extensor digitorum communis (27-27%) percentage decreased further. The even more distal, pronator quadratus (21-20%) and abuctor digiti minimi (17-17%) presented as muscles with low incidence of H-reflex positivity. In extensor indicis proprius (3%) the lowest H-potential incidence was found and in opponens pollicis no H-potential at all. F-waves if evaluated as "F-frequency" follow the similar distribution pattern. The lowest "F-frequency" was found on the legs in anterior tibial, short peroneal and extensor digitorum brevis muscles. In the last one more than one half of stimuli failed to evoke the F-potential. Those are the muscles in which H-potentials almost never appeared. The highest "F-frequency" was recorded in thigh, posterior lower leg muscle and flexor hallucis brevis. Some of the examinees displayed in almost all examined muscles H-potential (6 of 30), the others (9 of 30) had it in neither one or in a single muscle. It looks like as if a kind of H-reflex or F-wave individuals exist. If the H- or F-potentials distribution pattern got projected on the homunculus in quadrupedal position the following idea appears. The thigh muscles, the plantar flexors of the feet and hand and finger flexors are first of all tonic muscles mostly involved in standing or holding. The extensors of the foot/toes, respectively of hand/fingers interrupt phasically the sustained action of standing by lifting the foot/hand from the ground. The muscles with mostly tonic function produce much H-reflexes, transitional forms or at least F-wave with high "F-frequency". Is that a kind of phylogenetical remnants, better developed in the motorically less differentiated legs? Have the H-reflex muscles if compared with F-wave muscles different motor units structure? Have they different motoneurons, with different liability to produce recurrent discharges?