Human hands-and-knees crawling movement analysis based on time-varying synergy and synchronous synergy theories.

This paper aims to investigate human hands-and-knees crawling movement from the aspect of synchronous (SYN) and time-varying (TV) muscle synergy analysis. Nine healthy children and 11 children with cerebral palsy were recruited. During hands-and-knees crawling, surface electromyography (sEMG) signals from 12 main muscles of upper limbs and trunk were recorded, and muscle synergies were extracted based on TV synergy and SYN synergy theories. From the perspectives of repeatability, symmetry and similarity, the abilities of these two types of synergies to characterize crawling movement and to distinguish normal and abnormal crawling were explored. We found that: First, SYN synergy is better than TV synergy in depicting the body symmetry during crawling movement. However, TV synergy is more suitable than SYN synergy for distinguishing normal and abnormal crawling from the perspective of symmetry. Second, the abilities of SYN synergy and TV synergy in depicting the crawling repeatability are not comparable, and both have the potential to depict the crawling abnormality from the perspective of repeatability. Third, from the angle of inter-subject similarity, SYN synergy has the potential to describe the abnormal crawling pattern. However, the large individual differences suggest that TV synergy is a poor choice. This study provides a new way to analyze crawling movement from the perspective of neuromuscular control, and the research findings are meaningful for clinical assessment of abnormal crawling.