Analysis of the Inter-Joints Synergistic Patterns of Limbs in Infant Crawling.

Hands and knees crawling is an important motor developmental milestone, which is characterized by diagonal coordination between upper and lower limbs. However, the features of inter-joint synergy within each limb in infant crawling is still not clear. Therefore, the aim of this study was to extract the inter-joint synergistic patterns during infant crawling and to test the possibilities of using the extracted inter-joint synergy to distinguish developmental delayed (DD) infants from typical developing (TD) infants. In this paper, kinematic data were collected from the shoulder, elbow, wrist, hip, knee, and ankle joints when 9 TD infants and 9 DD infants were crawling on hands and knees at their self-selected velocity. Tangential velocity was firstly calculated from the three-dimensional (3D) trajectory of each joint. Then, the non-negative matrix factorization (NMF) method was used to extract the joints synergistic patterns of each limb from the tangential velocity data. Our preliminary results showed that the crawling movement could be represented by a joint synergistic pattern, which consisted of three joints' data. In addition, we observed that the distal joint had a greater impact than the proximal joints during infant crawling. Moreover, it was found that the DD infants could be preliminarily distinguished from the TD infants by the features of inter-joint synergy during their crawling stage.