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Control of foot trajectory in walking toddlers: adaptation to load changes
Nadia Dominici1, Yuri P Ivanenko, Francesco Lacquaniti
1Department of Neuromotor Physiology, Santa Lucia Foundation, University of Rome Tor Vergata, Rome, Italy.
Insights
Toddlers learning to walk struggle to adjust their gait when their body weight changes. It takes months of practice for young children to effectively manage load variations during locomotion.
Area of Science:
- Biomechanics
- Developmental Motor Control
- Human Locomotion
Background:
- Terrestrial locomotion relies on load-regulating mechanisms to manage body weight.
- Understanding how toddlers adapt to their own body weight during initial walking is crucial for developmental studies.
Purpose of the Study:
- To investigate the impact of body weight variations on the walking patterns of toddlers during their first unsupported steps.
- To compare the adaptive responses of toddlers, intermediate walkers, and adults to altered gravitational loads.
Main Methods:
- Studied 12 toddlers, 15 older children, and 10 adults stepping on a force platform.
- Simulated reduced body weight by an experimenter applying upward force to the subject's trunk.
- Analyzed foot path trajectories and kinematic coordination under varying load conditions.
Main Results:
- Toddlers exhibited distinct foot path shapes (single-peak toe trajectory) compared to older children and adults (double-peak).
- Reduced body weight significantly altered toddlers' foot trajectory, causing high lifts and forward overshoot.
- Toddlers showed less kinematic coordination adjustment to load changes than older individuals.
Conclusions:
- Early walkers do not accurately compensate for changes in vertical body loads using their kinematic controllers.
- Developing effective compensation for load variations requires several months of independent walking experience.
- Motor control systems for upright locomotion mature over time, enabling better adaptation to body weight fluctuations.
Abstract:
On earth, body weight is an inherent constraint, and accordingly, load-regulating mechanisms play an important role in terrestrial locomotion. How do toddlers deal with the effects of their full body weight when faced with the task of independent upright locomotion for the first time? Here we studied the effect of load variation on walking in 12 toddlers during their first unsupported steps, 15 older children (1.3-5 yr), and 10 adults. To simulate various levels of body weight, an experimenter held the trunk of the subject with both hands and supplied an approximately constant vertical force during stepping on a force platform. During unsupported stepping, the shape of the foot path in toddlers (typically single-peak toe trajectory) was different from that of adults and older children (double-peak trajectory). In contrast to adults and older children, who showed only limited changes in kinematic coordination, the "reduced-gravity" condition considerably affected the shape of the foot path in toddlers: they tended to make a high lift and forward foot overshoot at the end of swing. In addition, stepping at high levels of body unloading was characterized by a significant change in the initial direction of foot motion during early swing. Intermediate walkers (1.5-5 mo after walking onset) showed only partial improvement in foot trajectory characteristics. The results suggest that, at the onset of walking, changes in vertical body loads are not compensated accurately by the kinematic controllers; compensation necessitates a few months of independent walking experience.
