Spatially distributed sequential stimulation applied to the paralyzed quadriceps muscles while performing motor-assisted FES cycling

Spatially distributed sequential stimulation (SDSS) demonstrated greater fatigue-reducing ability and power output when performing isometric or isokinetic contractions of the paralyzed quadriceps muscles compared to the equivalent conventional functional electrical stimulation (FES) in a single electrode stimulation (SES) configuration. The present study aims to systematically assess the power output and fatigue-reducing properties of SDSS versus SES applied to the paralyzed quadriceps muscles of subjects performing motor-assisted FES cycling. Four subjects (three with spinal cord injury and one with multiple sclerosis) without lower-limb motor function participated in two multiday experimental sessions, each with both SDSS and SES stimulation phases. The results of the present study show that muscles stimulated with SDSS produced a significantly higher mean power (10.5 W ± 1.2 W) compared to SES (4.3 W ± 1.4 W), corresponding to an increase of approximately 144%, while inducing a similar amount of muscle fatigue (SDSS: 68.9% ± 8.0% vs. SES: 75.3% ± 13.4%). These findings suggest that SDSS is superior to SES when applied to paralyzed quadriceps muscles of the subjects performing FES cycling using moderate-intensity stimulation. Further research with larger sample size is needed to ascertain these findings and to explore applications of SDSS on FES cycling and FES exercise in general, over longer stimulation sessions under high-intensity stimulation conditions.