It is commonly assumed that exaggerated stretch reflex activity and the resulting increased muscle tone in ankle plantar flexors contribute to reduced ankle joint movement during gait in children with cerebral palsy (CP). We investigated the contribution of sensory feedback mechanisms to ankle plantar flexor muscle activity during treadmill walking in 20 children with CP and 41 control children. Stretch responses in plantar flexor muscles evoked in stance by dorsiflexion perturbations showed an age-related decline in control children but not in children with CP. In swing responses were abolished in control children, but not in children with CP. Removal of sensory feedback to the soleus muscle in stance by shortening the plantar flexors produced a drop in soleus EMG activity of a similar size and latency in control children and children with CP. Soleus EMG activity was observed in swing in a similar proportion in both groups. Shortening of the plantar flexors in swing caused a larger drop in Soleus EMG in control children than in children with CP. The lack of age related decline in stretch reflexes in the stance phase and the inability to suppress the reflex in the swing phase is likely related to lack of maturation of corticospinal control in children with CP. However, since they did not show soleus EMG activity to a larger extent than control children in swing and since sensory afferent feedback did not contribute more to their muscle activity, spasticity is unlikely to contribute to foot drop and toe walking.
Journal of Neurophysiology, 2014, Vol 111, Issue 4, p. 746-754