BACKGROUND : Crawling is a key milestone in infant motor development, facilitating independent exploration of space and contributing to neuromuscular maturation. While kinematic studies have begun to characterize early crawling movement patterns, underlying muscle activity remains poorly understood. The present study aimed to provide a more comprehensive view of early crawling movements.
METHODS : Three-dimensional (3D) motion capture and surface electromyography (sEMG) of quadriceps femoris, hamstrings, tibialis anterior and triceps surae, were simultaneously recorded during 2 conditions, i.e. in prone and/or on the Crawliskate©, at the (corrected) age of 3 months, in typically developing (TD) infants and those at high-risk (HR) for neurodevelopmental disorders (NDD). Among 3D motion capture data, only 2D video data were analyzed to quantify movement frequencies, durations, and intra-individual variability in durations. sEMG data were analyzed to quantify antagonistic coactivation indices. For the latter two outcomes, participants were included only if they demonstrated more than 5 movement occurences, separately for each movement type. Statistical analyses were performed only for movement frequencies and durations between prone and Crawliskate© conditions in the TD group, using Wilcoxon signed-rank tests.
RESULTS : 22 TD infants (11 males, 3.0 months [3.0; 3.2]) and 3 infants at HR for NDD (3 females with no major brain lesion, chronological age: 6.2 months [5.3; 6.3], corrected age: 2.8 months [2.3; 2.8]) were analyzed. Among TD infants, 10 contributed to both the prone and Crawliskate© conditions. All HR infants contributed only to the prone condition. No statistically significant difference was found for movement frequencies and durations between prone and Crawliskate© conditions in the TD group. However, several trends, along with the analysis of individual profiles, suggested that the Crawliskate© was associated with an increased frequency of leg steps, decreased frequency of leg kicks, shorter movement durations, and greater intra-individual variability in movement durations, compared to the prone condition. Moreover, in the HR group, step extensions were the most frequent movement type, and infants demonstrated fewer steps, more kicks, and overall shorter movement durations compared to TD infants. Regarding coactivation levels, no difference was observed, whether comparing conditions within the TD group, groups within the prone condition, or movement types within each condition and group.
DISCUSSION : These findings suggest that the Crawliskate© promotes early step movements by enhancing limb movement freedom. Our exploratory comparison between TD infants and those at HR for NDD, even without major brain lesion, highlight the value of early motor assessment in preterm populations.
FUTURE PERSPECTIVES : Future research should extend this framework through longitudinal designs with larger sample sizes (including infants with documented brain lesions), integrating upper and lower limb, full-cycle, bilateral analyses. Incorporating additional neuromuscular metrics (e.g., muscle synergies, spinal maps) and kinematic analyses obtained from both marker-based and markerless motion capture systems, may h
