title: Elastic, viscous, and mass load effects on poststroke muscle recruitment and co-contraction during reaching: a pilot study.
abstract: BACKGROUND
  Resistive exercise after stroke can improve strength (force-generating capacity) without increasing spasticity (velocity-dependent hypertonicity). However, the effect of resistive load type on muscle activation and co-contraction after stroke is not clear.
  
  
  OBJECTIVE
  The purpose of this study was to determine the effect of load type (elastic, viscous, or mass) on muscle activation and co-contraction during resisted forward reaching in the paretic and nonparetic arms after stroke.
  
  
  METHODS
  This investigation was a single-session, mixed repeated-measures pilot study.
  
  
  METHODS
  Twenty participants (10 with hemiplegia and 10 without neurologic involvement) reached forward with each arm against equivalent elastic, viscous, and mass loads. Normalized shoulder and elbow electromyography impulses were analyzed to determine agonist muscle recruitment and agonist-antagonist muscle co-contraction.
  
  
  RESULTS
  Muscle activation and co-contraction levels were significantly higher on virtually all outcome measures for the paretic and nonparetic arms of the participants with stroke than for the matched control participants. Only the nonparetic shoulder responded to load type with similar activation levels but variable co-contraction responses relative to those of the control shoulder. Elastic and viscous loads were associated with strong activation; mass and viscous loads were associated with minimal co-contraction.
  
  
  CONCLUSIONS
  A reasonable, but limited, range of loads was available.
  
  
  CONCLUSIONS
  Motor control deficits were evident in both the paretic and the nonparetic arms after stroke when forward reaching was resisted with viscous, elastic, or mass loads. The paretic arm responded with higher muscle activation and co-contraction levels across all load conditions than the matched control arm. Smaller increases in muscle activation and co-contraction levels that varied with load type were observed in the nonparetic arm. On the basis of the response of the nonparetic arm, this study provides preliminary evidence suggesting that viscous loads elicited strong muscle activation with minimal co-contraction. Further intervention studies are needed to determine whether viscous loads are preferable for poststroke resistive exercise programs.
authors.affiliation: Department of Physical Therapy, Marquette University, Schroeder Health Complex, PO Box 1881, Milwaukee, WI 53201-1881, USA. tina.stoeckmann@mu.edu
authors.forename: Tina M
authors.initials: TM
authors.lastname: Stoeckmann
authors.forename: Katherine J
authors.initials: KJ
authors.lastname: Sullivan
authors.forename: Robert A
authors.initials: RA
authors.lastname: Scheidt
mesh_terms: D000222:Adaptation, Physiological; D000368:Aged; D001132:Arm / Q000503:physiopathology; D004548:Elasticity; D004550:Elbow / Q000503:physiopathology; D005260:Female; D006429:Hemiplegia / Q000209:etiology / Q000503:physiopathology* / Q000534:rehabilitation*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010291:Paresis / Q000209:etiology / Q000534:rehabilitation*; D010865:Pilot Projects; D016059:Range of Motion, Articular; D020127:Recovery of Function; D011999:Recruitment, Neurophysiological; D012782:Shoulder / Q000503:physiopathology; D013314:Stress, Mechanical; D020521:Stroke / Q000150:complications; D000071939:Stroke Rehabilitation; D013647:Task Performance and Analysis; D014783:Viscosity; D016474:Weight-Bearing