Poor control of postural muscles is a primary impairment in cerebral palsy (CP), yet core trunk
and hip muscle activity has not been thoroughly investigated. Frequency analysis of
electromyographic (EMG) signals provides insight about the intensity and pattern of muscle
activation, correlates with functional measures in CP, and is sensitive to change after intervention.
The objective of this study was to investigate differences in trunk and hip muscle activation
frequency in children with CP compared to children with similar amounts of walking experience
and typical development (TD). EMG data from 31 children (15 with CP, 16 with TD) were
recorded from 16 trunk and hip muscles bilaterally. A time-frequency pattern was generated using
the continuous wavelet transform and instantaneous mean frequency (IMNF) was calculated at
each interval of the gait cycle. Functional principal component analysis (PCA) revealed that IMNF
was significantly higher in the CP group throughout the gait cycle for all muscles. Additionally,
stride-to-stride variability was higher in the CP group. This evidence demonstrated altered
patterns of trunk and hip muscle activation in CP, including increased rates of motor unit firing,
increased number of recruited motor units, and/or decreased synchrony of motor units. These
altered muscle activation patterns likely contribute to muscle fatigue and decreased
biomechanical efficiency in children with CP.