This study reports trunk and hip muscle activity during the early stages of walking in
children with CP compared to children with TD. Mean frequency of muscle activation
during walking was higher and more variable from stride-to-stride throughout the gait cycle
for the CP group than TD for all 8 muscles investigated. The higher mean frequency in the
CP group suggests altered patterns of muscle activation and motor unit recruitment. Higher
IMNF can result from increased rates of motor unit firing, increased number of recruited
motor units, or decreased synchrony of motor units [Hermens et al., 1992]. This is consistent
with literature suggesting excessive and dyscoordinated muscle activity in CP [Unnithan et
al., 1996b; van der Heide and Hadders-Algra, 2005]. Lam et al have suggested that higher
EMG median frequency contributes to muscle fatigue in children with CP [Lam et al.,
2005]. Additionally, excessive muscle activity is related to decreased biomechanical
efficiency, with muscle cocontraction explaining a significant amount of variability in the energy cost of walking in children with CP [Unnithan et al., 1996a]. The markedly increased
stride-to-stride variability in muscle activation patterns in the CP group may further imply
discoordination and immaturity of muscle behavior, because greater variability in other gait
measures is characteristic of immature walking patterns [Hausdorff et al., 1999]