The effect of variable frequency trains during FES cycling

The purpose of this paper is to investigate variable frequency stimulation patterns as a mean of increasing torque production and hence performance in FES cycling. Specific experiments were carried out on 6 healthy subjects using a motor to keep a constant cadence. We stimulated the quadricep muscle of both the legs and measured the torque produced at the crank. Three different patterns with the same number of stimulation pulses in the train and with an initial ramp modulation of the pulsewidth (PW) were compared: 1 constant frequency train (CFT) with an interpulse interval (IPI) of 50ms and 2 catchlike-inducing trains (CIT). The tested CIT had two different IPI of the remaining low-frequency part of the train (50ms and 55ms) and the doublet was always placed at the end of the PW ramp up.The results indicated that the CIT produced significantly greater torque time integrals and torque peaks than CFT both in fresh and fatigued muscles. In addition the CIT showed a lower reduction of the parameters tested between pre-fatigue and fatigue conditions.Our results suggest that stimulation with CIT increased the torque produced for each applied stimulation pulse improving the performance of FES cycling compared to CFT stimulation