H-reflex, F-wave, transitional and missed response frequency distribution in limb muscles.

The late potential analysis was performed in 86 neurologically healthy subjects aged 0 month to 6 years. The following muscles were analyzed: soleus, flexor hallucis brevis, extensor digitorum brevis and abductor pollicis brevis muscle. Late potentials were evaluated according to H, HF, F and Ms (missing potentials) attributes. The potential population in a particular muscle in an age group was considered as 100%; the type frequency for a particular muscle in different age groups is presented as absolute value and percentage. No age specific combination was found. As no age specificity was recorded, attempts were made to differentiate the muscle specificity potential type distribution. The mean (x) of potential type percentages of all age groups in the same muscle was calculated. Thus, in soleus muscle, the following response types were found: 29% H-reflex, 15% HF potentials, 45% F-waves and 11% Ms potentials. Flexor hallucis brevis muscles had: 3% H-reflex, 6% HF potentials, 85% F-waves and 6% Ms potentials. In extensor digitorum brevis, not a single H-reflex or HF potential was found, whereas F-waves were observed in 46% and Ms in 54%. Abductor pollicis brevis produced 1% H-reflex, 2% HF, 66% F-waves and 31% Ms potentials. Therefore, the soleus could be defined as a high percentage of H, HF, F and low Ms responses muscle. Flexor hallucis brevis and abductor pollicis brevis had high F, very low H, HF and low or moderate Ms response muscles. In the latter, the percentage of Ms potentials was significantly higher than in the former. A very high percentage of Ms potentials was found to be an outstanding attribute of extensor digitorum brevis, as it never develops H or HF but only F potentials. The occurrence of H, HF, F and Ms responses in different limb muscles corresponded closely to that found in adults. There was no significant correlation with age. The potential type frequency of occurrence in individual muscles with aging remained more or less constant. There was no correlation with nerve conduction velocities (significantly slower during the first months of life) either. The results appear to favor the genetic determination of the electrophysiological phenomena observed, through motor units structure and function.