title: Involuntary and voluntary muscle activation in children with unilateral cerebral palsy--relationship to upper limb activity.
abstract: BACKGROUND
  Spasticity and reduced strength are both primary neuromuscular impairments associated with cerebral palsy (CP). However, it is unclear whether spasticity or reduced strength is the strongest contributor to activity limitations.
  
  
  OBJECTIVE
  To study whether involuntary activation of the biceps brachii muscle, in addition to reduced strength, contributes to limitations in upper limb activity in children with CP.
  
  
  METHODS
  Fifteen children with unilateral CP (9 males and 6 females, age range 8-17 years) participated in this study. Involuntary activation, reflecting spasticity, was studied as biceps brachii activity during passive elbow extension at four isokinetic velocities (10, 90, 180 and 300°/s). Elbow flexion peak torque, reflecting strength, was measured during maximal voluntary isometric contraction, and concurrent biceps brachii activity was registered reflecting voluntary muscle activation. Bimanual upper limb activity was assessed in the performance domain using the Assisting Hand Assessment (AHA).
  
  
  RESULTS
  Both involuntary and voluntary muscle activation were related to activity, the former negatively, but voluntary activation showed the strongest relationship (Spearmans rho = .84). Involuntary muscle activation at 10, 90 and 180°/s was negatively related to muscle strength (Spearmans rho = -.63, -.58 and -.62, respectively).
  
  
  CONCLUSIONS
  Our results do not indicate that spasticity affects upper limb activity in addition to strength. Most likely, muscle weakness and spasticity jointly contribute to activity limitations, reflected by the strong relationship between the ability to voluntarily activate a muscle and activity performance.
authors.affiliation: Clinical Services, St. Olavs University Hospital, Trondheim, Norway. siri.brendvik@stolav.no
authors.forename: Siri Merete
authors.initials: SM
authors.lastname: Brændvik
authors.forename: Ann-Kristin G
authors.initials: AK
authors.lastname: Elvrum
authors.forename: Beatrix
authors.initials: B
authors.lastname: Vereijken
authors.forename: Karin
authors.initials: K
authors.lastname: Roeleveld
mesh_terms: D000293:Adolescent; D002547:Cerebral Palsy / Q000503:physiopathology*; D002648:Child; D004550:Elbow / Q000503:physiopathology; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D009128:Muscle Spasticity / Q000503:physiopathology; D053581:Muscle Strength Dynamometer; D018908:Muscle Weakness / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D019415:Torque; D034941:Upper Extremity / Q000503:physiopathology*