Principal Component Analysis of Stair Negotiation and Floor Transition Kinematics in Older Adults With and Without Functional Disability: Cross-Sectional Study.

Background: Stair negotiation (ascending and descending) and transitions to level walking are complex motor tasks influenced by aging; yet the impact of functional disability on these changes remains underexplored. Objective: This study aimed to evaluate the lower limb joint positions, velocities, and the center of mass (CoM) displacement and velocity during stair negotiation and transitions in older adults with and without functional disability. Methods: Sixty community-dwelling adults, aged 60 years and older, were assessed for lower limb tridimensional joint positions and velocities during the instances of foot contact or leaving the step and foot contact or leaving the floor; the joint range of motion, angular velocity range, and the CoM displacement and angular velocity range were assessed during stair ascend and descend and transitions floor-to-stair and stair-to-floor through an optoelectronic system. Principal component analysis was used to assess 8 groups of variables to compute principal component models (I-VIII). Participants were classified as with or without disability based on functional disability indicators. Group differences were assessed using the Mann-Whitney U test. Results: From 240 variables, 41 key parameters were identified, mainly related to hip and knee angular velocities in the sagittal plane. Significant differences between older adults with disability (n=25) and without disability (n=35) were found in 12 principal components. Conclusions: Older adults with functional disability showed changes in the sagittal plane hip as well as in the knee angular velocity and mediolateral and vertical CoM displacement and velocity during stair negotiation and transitions. These findings can inform targeted strategies to improve mobility and stability in this population.