Full length article Synergy of EMG patterns in gait as an objective measure of muscle selectivity in children with spastic cerebral palsy Esther Zwaan *, Jules G. Becher, Jaap Harlaar Department of Rehabilitation Medicine, Research institute MOVE, VU University Medical Center, De Boelelaan 1117, 1088 HV Amsterdam, The Netherlands 1. Introduction Cerebral palsy (CP) is a disorder characterised by neurologic dysfunctions caused by damage to the central nervous system (CNS) during CNS development. Due to this CNS damage, children with CP have cognitive dysfunctions and motor problems. These motor problems can be divided into excess symptoms and deficiency symptoms. Excess features include hypertonia, tics, tremor [1], spasticity and hyper-reflexia [2], while deficiency features include muscular weakness, ataxia, apraxia [1] and loss of selective motor control. Selective motor control has been defined as ‘the ability to isolate the activation of muscles in a selected pattern in response to demands of a voluntary movement or posture’ [1]. This has been shown to be the most important determinant of gross motor function progress as measured by the gross motor function measure (GMFM) [3]. The GMFM is a standardized observational instrument that measures gross motor function in children with CP, based on their performance of 66 gross motor tasks upon instruction in a specific test situation [4,5]. The loss of selective motor control leads to synergistic movement patterns. In stroke research it was found that when individuals with stroke attempt to abduct at the paretic shoulder under isometric conditions, abnormal muscle coactivation occurs between the shoulder abductors and elbow flexors, known as an arm flexor synergy [6]. To explain this, three mechanisms for abnormal muscle co-activation are suggested which may also help our understanding of lack of selective muscle control in CP: increased dependence on residual brainstem descending path- ways, increased overlap of cortical representation and changes in spinal cord excitability [6–11]. In recent years, there has been growing interest in selective motor control as a predictive indicator of motor function in cerebral palsy. The assessment of selective motor control ability for children with CP was first described by Staudt and Peacock [12]. These researchers assessed selective motor control by asking the child to perform isolated motions at the hip, knee and ankle in various combinations. They used this test for patient selection for selective posterior rhizotomy. Later, Boyd and Graham [13] developed the selective motor control (SMC) of dorsiflexion scale to establish changes in motor performance after treatment with botulinum toxin type A. The child was requested to dorsiflex each foot to a target. The basis of this MC scale was the child’s ability to activate the dorsiflexors in isolation. The interrater reliability varied between fair/good to strong and the test–retest reliability Gait & Posture 35 (2012) 111–115 A R T I C L E I N F O Article history: Received 28 October 2010 Received in revised form 18 August 2011 Accepted 20 August 2011 Keywords: Cerebral palsy Selectivity EMG Gait Synergy A B S T R A C T Selective motor control (SMC) is an important determinant of functioning in cerebral palsy (CP). Currently its assessment is based on subjective clinical tests with a low sensitivity. Electromyography (EMG) profiles during gait represent muscle coordination and might be used to assess SMC. EMG measurements during gait were processed into a measure of extensor synergy and thigh synergy. This was obtained in two groups of children with CP, and 30 typically developing children. Extensor synergy in CP was higher (0.95) than in healthy children (0.77), thigh synergy was almost equal in both groups. GMFM scores in the first group of 39 children with CP did not correlate to EMG based synergy measures. In a second group of 38 children with CP, a clear relation of clinical SMC score with extensor synergy was found, but only a weak relation with thigh synergy. Although an extensor synergy was validated at group level, our results present no convincing evidence for the use of EMG during gait to assess SMC in individual subjects with CP. Since gait involves both synergistic and selective contractions, the inherent motor control properties of this task will not allow for an assessment of selectivity comparable to the ability to perform isolated movements. Nevertheless, our results support the sensitive nature of EMG to represent an aberrant motor control in CP. ß 2011 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +31 627426909. E-mail address: estherzwaan@live.nl (E. Zwaan). Contents lists available at SciVerse ScienceDirect Gait & Posture jo u rn al h om ep age: ww w.els evier.c o m/lo c ate/g aitp os t 0966-6362/$ – see front matter ß 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2011.08.019