Decomposition of spontaneous movements of infants as combinations of limb synergies

Abstract

We hypothesized that a variety of limb movements in infants, including spontaneous movements and movements during interactions with the environment, can be represented as combinations of limb synergies, which are building blocks for generating coordinated movements of multiple limbs. A decomposition algorithm based on a nonnegative matrix factorization was applied to the discrete data segments taken from continuous data of limb movements in 298 infants (age, 3-4 months). The data were linearly decomposed into bases, which were referred to as synergies. The results showed that approximately 70% of the variance in the velocity profiles of the data segments of the four limbs can be explained by a set of five simple synergies that represent single-limb movements and the synchronous movement of all limbs. The present method showed that the complex properties of limb movements can be represented as combinations of synergies. Furthermore, comparisons of movement patterns across different age groups showed that in older infants, the contribution ratios of each synergy were different between spontaneous movements and movements during playing with a toy, whereas in younger infants, there were no differences in the contribution ratios between the different movement conditions. These results demonstrate that decomposition into limb synergies is useful for determining the spatiotemporal properties of interlimb coordination during spontaneous movements and task-constrained movements in infants.

Multiple patterns of infant rolling in limb coordination and ground contact pressure

“…This suggests the importance of understanding the development of rolling not as a change from one pattern to another but rather as a change from one set of patterns to another set of patterns. Previous studies showed the complex patterns of spontaneous in infants (Watanabe and Taga 2011;Kanemaru et al 2012;Kato et al 2013Kato et al , 2014Ohmura et al 2016). However, distinguishing individual variability from intra-individual variability is challenging.…”

Abnormal interlimb coordination of motor developmental delay during infant crawling based on kinematic synergy analysis

“…NMF can decompose the multi-joint velocities for limb movement into two components: the time-invariant kinematic synergies combining by all joints with different weightings, and the time-varying activation coefficients representing the activation patterns of corresponding synergies [ 22 , 26 ]. Kato et al successfully employed the NMF algorithm to derive kinematic synergies from the tangential velocities of joints of the four limbs for spontaneous movements of infants, where these synergies represented the dominance of different combinations of limbs [ 27 ]. Since the tangential velocities of joints do not include the direction of limb movement in space, the analytical complexity of limb movement can be highly reduced [ 27 , 28 ].…”

“…Kato et al successfully employed the NMF algorithm to derive kinematic synergies from the tangential velocities of joints of the four limbs for spontaneous movements of infants, where these synergies represented the dominance of different combinations of limbs [ 27 ]. Since the tangential velocities of joints do not include the direction of limb movement in space, the analytical complexity of limb movement can be highly reduced [ 27 , 28 ]. Although our pilot study has preliminarily distinguished infants with MDD from typically developing (TD) infants by the kinematic synergies of tangential velocities of joints during crawling [ 29 ], it is less clear how MDD affects interlimb coordination based on those synergies.…”

“…Under the synergy analysis framework, researchers have proposed a few kinematic features to objectively quantify interlimb coordination during human movement. For instance, the variability accounted for (VAF) as calculated from original and decomposed matrices and the synergy weightings of each MU in the derived synergies have been used to measure the stability of joints and limbs for limb movement, which can be changed in individuals with neurological diseases [ 8 , 27 ]. During human movement, the full width at half maximum (FWHM) and center of activity (CoA) of activation coefficients can effectively characterize the differences in the activation levels of corresponding synergies not only between TD children and children with neurological diseases but also among various motor behaviors [ 9 , 30 , 31 ].…”

Measurement and Analysis of Human Infant Crawling for Rehabilitation: A Narrative Review

“…For example, quantitative analysis of arm-leg coordination has been performed in neonates' stepping and demonstrated a neural coupling between the arms and legs ( 13 ). Then, spontaneous movements around 2 months have been shown to display some primitive forms of coordinative behavior between arms and legs ( 14 ). Much later, at approximately the age of 9 months, infant's creeping behavior begins with the clumsy attempts to move forward with the abdomen touching the ground.…”