title: The relation between spasticity and muscle behavior during the swing phase of gait in children with cerebral palsy.
abstract: There is much debate about how spasticity contributes to the movement abnormalities seen in children with spastic cerebral palsy (CP). This study explored the relation between stretch reflex characteristics in passive muscles and markers of spasticity during gait. Twenty-four children with CP underwent 3D gait analysis at three walking velocity conditions (self-selected, faster and fastest). The gastrocnemius (GAS) and medial hamstrings (MEHs) were assessed at rest using an instrumented spasticity assessment that determined the stretch-reflex threshold, expressed in terms of muscle lengthening velocity. Muscle activation was quantified with root mean square electromyography (RMS-EMG) during passive muscle stretch and during the muscle lengthening periods in the swing phase of gait. Parameters from passive stretch were compared to those from gait analysis. In about half the children, GAS peak muscle lengthening velocity during the swing phase of gait did not exceed its stretch reflex threshold. In contrast, in the MEHs the threshold was always exceeded. In the GAS, stretch reflex thresholds were positively correlated to peak muscle lengthening velocity during the swing phase of gait at the faster (r = 0.46) and fastest (r = 0.54) walking conditions. In the MEHs, a similar relation was found, but only at the faster walking condition (r = 0.43). RMS-EMG during passive stretch showed moderate correlations to RMS-EMG during the swing phase of gait in the GAS (r = 0.46-0.56) and good correlations in the MEHs (r = 0.69-0.77) at all walking conditions. RMS-EMG during passive stretch showed no correlations to peak muscle lengthening velocity during gait. We conclude that a reduced stretch reflex threshold in the GAS and MEHs constrains peak muscle lengthening velocity during gait in children with CP. With increasing walking velocity, this constraint is more marked in the GAS, but not in the MEHs. Hyper-activation of stretch reflexes during passive stretch is related to muscle activation during the swing phase of gait, but has a limited contribution to reduced muscle lengthening velocity during swing. Larger studies are required to confirm these results, and to investigate the contribution of other impairments such as passive stiffness and weakness to reduced muscle lengthening velocity during the swing phase of gait.
authors.affiliation: KU Leuven Department of Rehabilitation Sciences, Tervuursevest 101, 3001 Leuven, Belgium; Clinical Motion Analysis Laboratory, University Hospital, Pellenberg, Weligerveld 1, 3212 Pellenberg, Belgium. Electronic address: Lynn.Baron@faber.kuleuven.be.
authors.forename: Lynn
authors.initials: L
authors.lastname: Bar-On
authors.affiliation: Clinical Motion Analysis Laboratory, University Hospital, Pellenberg, Weligerveld 1, 3212 Pellenberg, Belgium; KU Leuven Department of Development and Regeneration, Herestraat 49 box 7003, 3000 Leuven, Belgium; Department of Orthopedics, University Hospital, Pellenberg, Weligerveld 1, 3212 Pellenberg, Belgium. Electronic address: Guy.Molenaers@uzleuven.be.
authors.forename: Guy
authors.initials: G
authors.lastname: Molenaers
authors.affiliation: KU Leuven Department of Mechanical Engineering, Celestijnenlaan 300b box 2420, 3001 Leuven, Belgium. Electronic address: Erwin.Aertbelien@kuleuven.be.
authors.forename: Erwin
authors.initials: E
authors.lastname: Aertbeliën
authors.affiliation: Clinical Motion Analysis Laboratory, University Hospital, Pellenberg, Weligerveld 1, 3212 Pellenberg, Belgium; KU Leuven Department of Mechanical Engineering, Celestijnenlaan 300b box 2420, 3001 Leuven, Belgium. Electronic address: Davide.Monari@kuleuven.be.
authors.forename: Davide
authors.initials: D
authors.lastname: Monari
authors.affiliation: KU Leuven Department of Rehabilitation Sciences, Tervuursevest 101, 3001 Leuven, Belgium. Electronic address: Hilde.Feys@faber.kuleuven.be.
authors.forename: Hilde
authors.initials: H
authors.lastname: Feys
authors.affiliation: KU Leuven Department of Rehabilitation Sciences, Tervuursevest 101, 3001 Leuven, Belgium; Clinical Motion Analysis Laboratory, University Hospital, Pellenberg, Weligerveld 1, 3212 Pellenberg, Belgium. Electronic address: Kaat.Desloovere@uzleuven.be.
authors.forename: Kaat
authors.initials: K
authors.lastname: Desloovere
mesh_terms: D000293:Adolescent; D001696:Biomechanical Phenomena; D002547:Cerebral Palsy / Q000150:complications / Q000503:physiopathology*; D002648:Child; D015331:Cohort Studies; D004576:Electromyography; D005260:Female; D020233:Gait Disorders, Neurologic / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D008297:Male; D009128:Muscle Spasticity / Q000209:etiology / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D011446:Prospective Studies; D012021:Reflex, Abnormal / Q000502:physiology; D012026:Reflex, Stretch / Q000502:physiology
keywords: Cerebral palsy; Electromyography; Gait; Muscle lengthening velocity; Spasticity; Stretch reflex