title: Spastic cocontraction in hemiparesis: effects of botulinum toxin.
abstract: BACKGROUND
  In this study of spastic hemiparesis we evaluated cocontraction during sustained agonist/antagonist efforts, before and after botulinum toxin (BoNT) injection in 1 agonist.
  
  
  METHODS
  Nineteen hemiparetic subjects performed maximal isometric elbow flexion/extension efforts with the elbow at 100° (extensors stretched). Using flexor and extensor surface electromyography we calculated agonist recruitment/cocontraction indices from 500-ms peak voluntary agonist recruitment, before and 1 month after onabotulinumtoxinA injection (160 U) into biceps brachii.
  
  
  RESULTS
  Before injection, agonist recruitment and cocontraction indices were higher in extensors than flexors [0.74 ± 0.15 vs. 0.59 ± 0.10 (P < 0.01) and 0.43 ± 0.25 vs. 0.25 ± 0.13 (P < 0.05), respectively]. Biceps injection decreased extensor cocontraction index (-35%, P < 0.05) while increasing flexor agonist recruitment and cocontraction indices.
  
  
  CONCLUSIONS
  In spastic hemiparesis, stretch may facilitate agonist recruitment and spastic cocontraction. In the non-injected antagonist, cocontraction may be reduced by enhanced reciprocal inhibition from a more relaxed, and therefore stretched, agonist, or through decreased recurrent inhibition from the injected muscle.
authors.affiliation: Arts et Métiers ParisTech, Laboratoire de Biomécanique, Paris, France. maria.vinti@neuf.fr
authors.forename: Maria
authors.initials: M
authors.lastname: Vinti
authors.forename: Filomena
authors.initials: F
authors.lastname: Costantino
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bayle
authors.forename: David M
authors.initials: DM
authors.lastname: Simpson
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Weisz
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Gracies
mesh_terms: D000328:Adult; D000368:Aged; D019274:Botulinum Toxins, Type A / Q000627:therapeutic use*; D004311:Double-Blind Method; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D009128:Muscle Spasticity / Q000188:drug therapy* / Q000209:etiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000503:physiopathology; D009465:Neuromuscular Agents / Q000627:therapeutic use*; D010291:Paresis / Q000150:complications*; D018709:Statistics, Nonparametric; D016896:Treatment Outcome
chemical_list: D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A