title: Comparison of stimulation patterns for FES-cycling using measures of oxygen cost and stimulation cost.
abstract: OBJECTIVE
  The energy efficiency of FES-cycling in spinal cord injured subjects is very much lower than that of normal cycling, and efficiency is dependent upon the parameters of muscle stimulation. We investigated measures which can be used to evaluate the effect on cycling performance of changes in stimulation parameters, and which might therefore be used to optimise them. We aimed to determine whether oxygen cost and stimulation cost measurements are sensitive enough to allow discrimination between the efficacy of different activation ranges for stimulation of each muscle group during constant-power cycling.
  
  
  METHODS
  We employed a custom FES-cycling ergometer system, with accurate control of cadence and stimulated exercise workrate. Two sets of muscle activation angles ("stimulation patterns"), denoted "P1" and "P2", were applied repeatedly (eight times each) during constant-power cycling, in a repeated measures design with a single paraplegic subject. Pulmonary oxygen uptake was measured in real time and used to determine the oxygen cost of the exercise. A new measure of stimulation cost of the exercise is proposed, which represents the total rate of stimulation charge applied to the stimulated muscle groups during cycling. A number of energy-efficiency measures were also estimated.
  
  
  RESULTS
  Average oxygen cost and stimulation cost of P1 were found to be significantly lower than those for P2 (paired t-test, p<0.05): oxygen costs were 0.56+/-0.03l min-1 and 0.61+/-0.04l min-1 (mean+/-S.D.), respectively; stimulation costs were 74.91+/-12.15 mC min-1 and 100.30+/-14.78 mC min-1 (mean+/-S.D.), respectively. Correspondingly, all efficiency estimates for P1 were greater than those for P2.
  
  
  CONCLUSIONS
  Oxygen cost and stimulation cost measures both allow discrimination between the efficacy of different muscle activation patterns during constant-power FES-cycling. However, stimulation cost is more easily determined in real time, and responds more rapidly and with greatly improved signal-to-noise properties than the ventilatory oxygen uptake measurements required for estimation of oxygen cost. These measures may find utility in the adjustment of stimulation patterns for achievement of optimal cycling performance.
authors.affiliation: Centre for Rehabilitation Engineering, Department of Mechanical Engineering, University of Glasgow, and Queen Elizabeth National Spinal Injuries Unit, Southern General Hospital, 1345 Govan Road, Glasgow G51 4TF, UK. k.hunt@mech.gla.ac.uk
authors.forename: K J
authors.initials: KJ
authors.lastname: Hunt
authors.forename: C
authors.initials: C
authors.lastname: Ferrario
authors.forename: S
authors.initials: S
authors.lastname: Grant
authors.forename: B
authors.initials: B
authors.lastname: Stone
authors.forename: A N
authors.initials: AN
authors.lastname: McLean
authors.forename: M H
authors.initials: MH
authors.lastname: Fraser
authors.forename: D B
authors.initials: DB
authors.lastname: Allan
mesh_terms: D001698:Biomedical Engineering; D004599:Electric Stimulation Therapy / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D005080:Exercise Test / Q000295:instrumentation / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology; D010100:Oxygen / Q000502:physiology; D010264:Paraplegia / Q000503:physiopathology / Q000628:therapy; D013119:Spinal Cord Injuries / Q000503:physiopathology* / Q000628:therapy*
chemical_list: D010100:Oxygen