Adaptability in infant walking

PROJECT SUMMARY A hallmark of functional motor skill is adaptability—tailoring movements to changes in the body or environment. The proposed project focuses on adaptability in infant walking because infants must learn to walk in the midst of continual changes in their bodies and environments. Changes in the body (due to physical growth, carrying

objects, footwear, etc.) and environment (varying ground surfaces, obstacles, etc.) alter the biomechanical constraints on balance, propulsion, and braking. Moreover, walking is a foundational motor skill, endemic in everyday activity, and central to clinical assessment and intervention. The central hypothesis is that infants acquire adaptability via everyday walking experience. That is, infants

learn strategies for modifying their walking patterns (footfalls and joint angles) as they navigate an ever-changing environment in a continually changing body. A century of research shows that infants’ age and everyday walking experience (elapsed time since walk onset) predict their skill when walking barefoot over flat ground. But little

work examined infants’ ability to modify their walking patterns (speed, step length, joint angles, etc.) to cope with changes in their body or environment. Thus, the proposed project fills an empirical gap in scientific knowledge that is fundamental to developmental theory. The proposed experiment tests the role of everyday walking experience in the development of

adaptability in infant walking. Because age and walking experience are confounded, the proposed experiment uses a within-subjects, age-held-constant design—all 14-month-old infants to control for age while walking experience (0-4 months) varies freely. Infants will be tested in a baseline condition (walking barefoot over a flat

walkway) and in 4 novel conditions that require adaptability—2 body conditions (walking over a flat walkway wearing shoes that tilt their toes 10° up or 10° down); and 2 environment conditions (walking barefoot over a sloping walkway tilted 10° up or 10° down). The shoe conditions affect infants’ balance; the slope conditions

affect balance, propulsion, and braking. Spatiotemporal footfall measures, joint angles, and gait disruptions will characterize how infants modify their walking to cope with the novel challenges. Aim 1 tests whether infants display different walking patterns in each condition, and whether walking experience

is related to the type and diversity of patterns. Aim 2 assesses the similarity in walking between conditions for each infant, and tests whether walking experience amplifies the similarity or dissimilarity between conditions. Both aims leverage the power of machine learning analyses (density peak clustering and similarity matrices) to

fully characterize infants’ walking within and across conditions. The within-subjects, age-held-constant design, innovative body-environment test conditions, and analytic techniques provide a strong test of the long-term objective: to understand the role of experience in the development of adaptability in infant motor skill. Findings

promise to inform early intervention practices to support children’s locomotor development.