Abstract

Direct stimulation of muscle fibres with a regular 10 Hz rate, three computer generated random rhythms and a sequence of voluntary discharges was used to quantify the interdischarge interval (IDI) dependent jitter due to velocity recovery function (VRF). This jitter was found to depend on conduction time and strength of VRF, but not on propagation velocity. The results suggest that in the usual jitter study in voluntarily activated muscle fibre pairs, with moderately irregular discharge rate and interpotential intervals below 3 ms the IDI dependent jitter contributes on average less than 10 microseconds, but can be so large as to produce false abnormal values at more irregular rates, longer interpotential intervals and pronounced differences in VRF. It can be effectively removed by mathematical algorithms or, better still, by using electrical stimulation.