Analysis of cerebral palsy gait based on movement primitives.

BACKGROUND: Cerebral palsy is the most prevalent motor disorder among children. Despite extensive studies on motor modularity of gait of children with cerebral palsy, kinematic modularity of their gait has not been addressed which is the main goal of this study. METHODS: The kinematics of the gait of 13 typical development children and 188 children with cerebral palsy was captured and analyzed, where the cerebral palsy children were grouped into True, Jump, Apparent, and Crouch. Non-negative matrix factorization method was used to extract the kinematic modulus of each group, which were then clustered to find their characteristic movement primitives. The movement primitives of groups were then matched based on the similarity of their activation profiles. FINDINGS: The number of movement primitives was three for the Crouch group, four for the other cerebral palsy groups, and five for the typical development group. Compared to the typical development children, the kinematic modules and activations of the cerebral palsy groups involved higher variability and co-activation, respectively (P < 0.05). Three temporally matched movement primitives were shared by all groups, but with altered structures. INTERPRETATION: The gait of children with cerebral palsy involved lower complexity and higher variability due to the reduced and inconsistent kinematic modularity. Three basic movement primitives were sufficient to prodcue the overall gait kinematics, as observed in the Crouch group. Other movement primitives, were responsible for providing smooth transitions between basic movement primitives, as seen in more complex gait patterns.

The association between motor modules and movement primitives of gait: A muscle and kinematic synergy study.

In spite of the extensive literature on the analysis of the muscle synergies during gait, the functionality of these synergies has not been studied in detail. This study explored the relationship between the motor modules and the kinematic maneuvers involved in human walking. Motion and surface electromyography data (of 28 trunk and lower extremity muscles) were acquired from ten healthy subjects during ten trials of self-selected speed gait each. The joint angle trajectories were half-wave rectified and divided into two independent positive directional degrees-of-freedom. The muscle and kinematic synergies were both extracted using the non-negative matrix factorization (NNMF) technique and clustered via k-means method. Results indicated that for both the muscle and kinematic synergies, a same number of modules (five) could reconstruct the 200 limb-trial data reasonably well. Moreover, each individual muscle synergy was found to be associated with a single kinematic synergy, based on the similar activation periods of the paired muscle and kinematic modules and the high correlation of their activation patterns (r = 0.88 ± 0.05), with a consistent phase advance for muscle synergies (mean = 7.59 ± 2.34 %). It was concluded that there is a one-to-one association between the motor modules and kinematic synergies, suggesting that each individual kinematic synergy, representing a movement primitive of human walking, might be implemented by recruitment of a paired motor module.