title: Muscle Synergies in Cycling after Incomplete Spinal Cord Injury: Correlation with Clinical Measures of Motor Function and Spasticity.
abstract: BACKGROUND
  After incomplete spinal cord injury (iSCI), patients suffer important sensorimotor impairments, such as abnormal locomotion patterns and spasticity. Complementary to current clinical diagnostic procedures, the analysis of muscle synergies has emerged as a promising tool to study muscle coordination, which plays a major role in the control of multi-limb functional movements.
  
  
  OBJECTIVE
  Based on recent findings suggesting that walking and cycling share similar synergistic control, the analysis of muscle synergies during cycling might be explored as an early descriptor of gait-related impaired control. This idea was split into the following two hypotheses: (a) iSCI patients present a synergistic control of muscles during cycling; (b) muscle synergies outcomes extracted during cycling correlate with clinical measurements of gait performance and/or spasticity.
  
  
  METHODS
  Electromyographic (EMG) activity of 13 unilateral lower limb muscles was recorded in a group of 10 healthy individuals and 10 iSCI subjects during cycling at four different cadences. A non-negative matrix factorization (NNMF) algorithm was applied to identify synergistic components (i.e., activation coefficients and muscle synergy vectors). Reconstruction goodness scores (VAF and r (2)) were used to evaluate the ability of a given number of synergies to reconstruct the EMG signals. A set of metrics based on the similarity between pathologic and healthy synergies were correlated with clinical scales of gait performance and spasticity.
  
  
  RESULTS
  iSCI patients preserved a synergistic control of muscles during cycling. The similarity with the healthy reference was consistent with the degree of the impairment, i.e., less impaired patients showed higher similarities with the healthy reference. There was a strong correlation between reconstruction goodness scores at 42 rpm and motor performance scales (TUG, 10-m test and WISCI II). On the other hand, the similarity between the healthy and affected synergies presented correlation with some spasticity symptoms measured by Penn, Modified Ashworth and SCATS scales.
  
  
  CONCLUSIONS
  Overall, the results of this study support the hypothesis that the analysis of muscle synergies during cycling can provide detailed quantitative assessment of functional motor impairments and symptoms of spasticity caused by abnormal spatiotemporal muscle co-activation following iSCI.
authors.affiliation: Electronics Department, University of MinhoGuimarães, Portugal; Neural Rehabilitation Group, Cajal Institute, Spanish National Research CouncilMadrid, Spain.
authors.forename: Filipe O
authors.initials: FO
authors.lastname: Barroso
authors.affiliation: Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council Madrid, Spain.
authors.forename: Diego
authors.initials: D
authors.lastname: Torricelli
authors.affiliation: Sensorimotor Function Group - Hospital Nacional de Parapléjicos, Servicio de Salud de Castilla la Mancha (SESCAM)Toledo, Spain; iPhysio Research Group, San Jorge UniversityZaragoza, Spain.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Bravo-Esteban
authors.affiliation: Sensorimotor Function Group - Hospital Nacional de Parapléjicos, Servicio de Salud de Castilla la Mancha (SESCAM)Toledo, Spain; National Spinal Injuries Centre, Stoke Mandeville Spinal Research, Buckinghamshire Health Trust, National Health Service (NHS)Aylesbury, UK; Harris Manchester College, University of OxfordOxford, UK.
authors.forename: Julian
authors.initials: J
authors.lastname: Taylor
authors.affiliation: Sensorimotor Function Group - Hospital Nacional de Parapléjicos, Servicio de Salud de Castilla la Mancha (SESCAM)Toledo, Spain; Toledo Physiotherapy Research Group (GIFTO), Nursing and Physical Therapy School, Castilla la Mancha UniversityToledo, Spain.
authors.forename: Julio
authors.initials: J
authors.lastname: Gómez-Soriano
authors.affiliation: Electronics Department, University of Minho Guimarães, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Santos
authors.affiliation: Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council Madrid, Spain.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Moreno
authors.affiliation: Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council Madrid, Spain.
authors.forename: José L
authors.initials: JL
authors.lastname: Pons
keywords: cycling; motor function; muscle synergies; spasticity; spinal cord injury