Reduction of the muscle activity associated with self-imposed electrical stimulation of mixed nerves supplying lower limb muscles in man.

Similarly to brief hammer taps self-imposed on the limb segments, self-triggered electrical stimulation delivered to the tibial, femoral or peroneal nerves are associated with anticipatory reduction in the muscle activity (RMA) of the target leg muscles. The anticipatory RMA starts shortly before the expected perturbation and lasts until the onset of the impact. The purpose of the present work is to study to what extent the selective activation of the different homonymous and heteronymous afferents could modify the central programs and the associated time and space distribution of the anticipatory RMA pattern in the target leg muscles. Our results show that the anticipatory RMA pattern is a result mainly of a pre-programmed non-specific central command, rather than consequence of the specific composition of the afferent volleys originating from different homonymous and heteronymous nerves. The commands for the voluntary movement triggering the stimulation and the associated anticipatory RMA are closely linked but independently controlled. By their synchronisation and co-ordination the central nervous system accounts the differences in length of the particular motor pathways. It is suggested, that in contrast to the classic anticipatory postural adjustments, the anticipatory RMA is presumably an alternative mode of feed-forward control diminishing the undesired effects of the afferent inputs.