title: A biomechanical cause of low power production during FES cycling of subjects with SCI.
abstract: BACKGROUND
  The goal of Functional Electrical Stimulation (FES) cycling is to provide the health benefits of exercise to persons with paralysis. To achieve the greatest health advantages, patients should produce the highest possible mechanical power. However, the mechanical power output (PO) produced during FES cycling is very low. Unfavorable biomechanics is one of the important factors reducing PO. The purpose of this study was to investigate the primary joints and muscles responsible for power generation and the role of antagonistic co-contraction in FES cycling.
  
  
  METHODS
  Sixteen subjects with complete spinal cord injury (SCI) pedaled a stationary recumbent FES tricycle at 60 rpm and a workload of 15 W per leg, while pedal forces and crank angle were recorded. The joint muscle moments, power and work were calculated using inverse dynamics equations.
  
  
  RESULTS
  Two characteristic patterns were found; in 12 subjects most work was generated by the knee extensors in the propulsion phase (83% of total work), while in 4 subjects most work was shared between by the knee extensors (42%) and flexors (44%), respectively during propulsive and recovery phases. Hip extensors produced only low net work (12 & 7%). For both patterns, extra concentric work was necessary to overcome considerable eccentric work (-82 & -96%).
  
  
  CONCLUSIONS
  The primary power sources were the knee extensors of the quadriceps and the knee flexors of the hamstrings. The antagonistic activity was generally low in subjects with SCI because of the weakness of the hamstrings (compared to quadriceps) and the superficial and insufficient hamstring mass activation with FES.
authors.affiliation: Department of Neurology, Center for Sensorimotor Research, Ludwig-Maximilians University, Marchioninistrasse 23, Munich 81377, Germany. jszecsi@nefo.med.uni-muenchen.de.
authors.forename: Johann
authors.initials: J
authors.lastname: Szecsi
authors.forename: Andreas
authors.initials: A
authors.lastname: Straube
authors.forename: Che
authors.initials: C
authors.lastname: Fornusek
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004558:Electric Stimulation; D004734:Energy Metabolism / Q000502:physiology*; D005081:Exercise Therapy / Q000295:instrumentation* / Q000379:methods; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000503:physiopathology*; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D013119:Spinal Cord Injuries / Q000503:physiopathology / Q000534:rehabilitation*