Trunk and hip muscle activity patterns in early walkers with and without cerebral palsy

Abstract

Poor control of postural muscles is a primary impairment in cerebral palsy (CP), however little is known about the activity of postural muscles during walking in individuals with CP. The objective of this study was to investigate differences in trunk and hip muscle activation patterns during the early stages of walking in children with CP compared to children with typical development (TD). Thirty-one children (16 TD, 15 CP) with an average of 28.5 months of walking experience participated. Electromyographic (EMG) data were collected from 16 trunk and hip muscles as participants walked at a self-selected pace over an instrumented walkway. Custom-written computer programs were used to identify the onset of muscle activity, and to generate instantaneous mean frequency (IMNF) curves. A functional principal component analysis was performed to determine differences in IMNF curves between groups. Linear regression analyses were performed to investigate relationships between gait parameters, muscle activation, and musculoskeletal measures. Group means were significantly lower in the CP group than the TD group for all spatiotemporal gait parameters measured. The CP group had greater percent activation and coactivation for all muscles except the external oblique. Greater hip adductor spasticity was related to increased abdominal muscle activity in the CP group. The CP group also had higher mean frequency throughout the gait cycle for all muscles. Higher IMNF can result from increased rates of motor unit activation, increased number of recruited motor units, or decreased synchrony of motor units, and may contribute to muscle fatigue in children with CP. Within the CP group, children classified as Gross Motor Function Classification System (GMFCS) level II demonstrated no differences in spatiotemporal parameters or percent muscle activation, but had greater gait symmetry and lower INMF for the trunk muscles, compared to the children classified as GMFCS level III. The potential influence of recording activity from adjacent trunk muscles is discussed, as well as the influence of the use of an assistive device by some children with CP. Postural muscle training during the early stages of walking in CP should be investigated to encourage the development of more functional and efficient movement strategies in these children.