ADAPTATIONS TO THE FOOT PLACEMENT STRATEGY WHILE WALKING THROUGH CLUTTERED ENVIRONMENTS
Creators: name: Kulkarni, Ashwini
Publisher: name: Purdue University Graduate School
Year: 2023
Subjects: classificationCode: 420701
subject: Biomechanics
classificationCode: 420703
subject: Motor control

description: A key mechanism to maintain balance during walking is the foot placement strategy, where the person steps in the direction of an impending fall. On a clear walkway, the foot placement strategy translates to maintaining a consistent relationship between the center of mass state and the base of support (a body-centric constraint on foot placement), which is reflected in a consistent step length. However, to safely navigate in the community, foot placement must maintain certain spatial relations with environmental features as well (environmental constraints on foot placement). For stepping over obstacles, the environmental constraint takes the form of targeting. That is, the feet must be placed at precise locations relative to the obstacle to minimize the likelihood of tripping. My dissertation focused on proactive adaptations to foot placements while navigating cluttered environments. I developed the interstep covariation (ISC) index that quantifies the covariation between consecutive foot placements relative to stationary, visible environmental features (an obstacle and a visual target). The across-step (or group) changes in this index indicate how the two constraints (body-centric and environmental) on foot placement are managed during adaptive gait tasks. I quantified how the ISC index changed (1) across steps while approaching and crossing an obstacle, (2) due to healthy aging and (3) when the proximity of two environmental features was systematically altered. Specifically, in Study 1, the ISC index was quantified for the obstacle crossing step for healthy younger and older adults. In Study 2, proactive changes in the ISC index as healthy young adults approached and crossed an obstacle were characterized. In Study 3, the changes in the dynamics of the across-step ISC index due to an additional visual stepping target in the approach to the obstacle were identified. I found that there exists a covariance strategy that healthy adults use to navigate the environment safely and successfully. First, I found that individuals prioritize the environmental constraint at the expense of the body-centric constraint when the environment poses a larger risk to balance (the obstacle), or to satisfy a specified constraint (stepping on a visual target). Second, I found that the shift in prioritization is proactive, i.e., it occurs while approaching an obstacle. The strategy to shift priorities is influenced by age (Study 1), environmental features (Study 2 and Study 3), and the proximity of two environmental features (Study 3). These studies add to the current understanding of foot placement control by demonstrating how this well-known and 15 fundamental strategy to maintain balance while walking is systematically influenced by the environment and task constraints. These findings can be further extended to study proactive and reactive adaptations during walking in different populations.