title: Does muscle coactivation influence joint excursions during gait in children with and without hemiplegic cerebral palsy? Relationship between muscle coactivation and joint kinematics.
abstract: BACKGROUND
  The theoretical role of muscle coactivation is to stiffen joints. The aim of this study was to assess the relationship between muscle coactivation and joint excursions during gait in children with and without hemiplegic cerebral palsy.
  
  
  METHODS
  Twelve children with hemiplegic cerebral palsy and twelve typically developing children underwent gait analysis at three different gait speeds. Sagittal hip, knee, and ankle kinematics were divided into their main components corresponding to joint excursions. A coactivation index was calculated for each excursion from the electromyographic envelopes of the rectus femoris/semitendinosus, vastus medialis/semitendinosus, or tibialis anterior/soleus muscles. Mixed linear analyses of covariance modeled joint excursions as a function of the coactivation index and limb.
  
  
  RESULTS
  In typically developing children, increased coactivation was associated with reduced joint excursion for 8 of the 14 linear models (hip flexion, knee loading, knee extension in stance, knee flexion in swing, ankle plantarflexion from initial contact to foot-flat, ankle dorsiflexion in stance and in swing). Conversely, ankle plantarflexion excursion at push-off increased with increasing tibialis anterior/soleus coactivation. In the involved limbs of the children with cerebral palsy, knee loading, ankle plantarflexion at push off, and ankle dorsiflexion in swing decreased, while hip extension increased, with increasing muscle coactivation.
  
  
  CONCLUSIONS
  The relationships between muscle coactivation and joint excursion were not equally distributed in both groups, and predominant in typically developing children. The results suggest that excessive muscle coactivation is not a cause of stiff-knee gait in children with hemiplegic cerebral palsy, but appears to be related to spastic drop foot.
authors.affiliation: Laboratoire d'analyse du mouvement, pôle Médecine Physique et Réadaptation, hôpital Saint Jacques, CHU Nantes, Nantes, France; Laboratoire de Traitement de l'Information Médicale INSERM U650, Brest, France. Electronic address: raphael.gross@chu-nantes.fr.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Gross
authors.affiliation: Laboratoire d'analyse du mouvement, pôle Médecine Physique et Réadaptation, hôpital Saint Jacques, CHU Nantes, Nantes, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Leboeuf
authors.affiliation: Equipe Biostatistique, Pharmacoépidémiologie et Mesures Subjectives en Santé, EA 4275, Université de Nantes, Nantes, France.
authors.forename: Jean Benoit
authors.initials: JB
authors.lastname: Hardouin
authors.affiliation: Laboratoire d'analyse du mouvement, pôle Médecine Physique et Réadaptation, hôpital Saint Jacques, CHU Nantes, Nantes, France.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Perrouin-Verbe
authors.affiliation: Laboratoire de Traitement de l'Information Médicale INSERM U650, Brest, France; Université de Bretagne Occidentale, Brest, France; CHRU Brest, Hôpital Morvan, service médecine physique et réadaptation, Brest, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Brochard
authors.affiliation: Laboratoire de Traitement de l'Information Médicale INSERM U650, Brest, France; Université de Bretagne Occidentale, Brest, France; CHRU Brest, Hôpital Morvan, service médecine physique et réadaptation, Brest, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Rémy-Néris
mesh_terms: D000843:Ankle Joint / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D002547:Cerebral Palsy / Q000503:physiopathology*; D002648:Child; D004576:Electromyography; D005528:Foot / Q000503:physiopathology; D005684:Gait / Q000502:physiology*; D006615:Hip / Q000503:physiopathology; D006801:Humans; D007717:Knee / Q000503:physiopathology; D007719:Knee Joint / Q000503:physiopathology; D016014:Linear Models; D009128:Muscle Spasticity / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000502:physiology*; D052097:Quadriceps Muscle / Q000503:physiopathology; D016059:Range of Motion, Articular / Q000502:physiology; D016138:Walking
keywords: Cerebral palsy; Electromyography; Gait; Kinematics; Muscle coactivation