STIMULATION-INDUCED DAMAGE IN RABBIT FAST-TWITCH SKELETAL-MUSCLES - AQUANTITATIVE MORPHOLOGICAL-STUDY OF THE INFLUENCE OF PATTERN AND FREQUENCY

The aim of this study was to determine whether muscle fibre degenerati on brought about by chronic low-frequency electrical stimulation was r elated to the pattern and frequency of stimulation. Rabbit fast-twitch muscles, tibialis anterior and extensor digitorum longus, were stimul ated for 9 days with pulse trains ranging in frequency from 1.25 Hz to 10 Hz. Histological data from these muscles were analysed with multiv ariate statistical techniques. At the lower stimulation frequencies th ere was a significantly lower incidence of degenerating muscle fibres. Fibres that reacted positively with an anti-neonatal antibody were mo st numerous in the sections that revealed the most degeneration. The d ependence on frequency was generally similar for the two muscles, but the extensor digitorum longus muscles showed more degeneration than th e tibialis anterior at every frequency. Muscles subjected to 10 Hz int ermittent stimulation showed significantly less degeneration than musc les stimulated with 5 Hz continuously, although the aggregate number o f impulses delivered was the same. The-incidence of degeneration in th e extensor digitorum longus muscles stimulated at 1.25 Hz was indistin guishable from that in control, unstimulated muscles; for the tibialis anterior muscles, this was also true for stimulation at 2.5 Hz. We co nclude that damage is not an inevitable consequence of electrical stim ulation. The influence of pattern and frequency on damage should be ta ken into account when devising neuromuscular stimulation regimes for c linical use.