Phase-specific trunk kinematics during functional mobility in very old adults

Age-related declines in mobility and postural control substantially increase fall risk among older adults. Functional mobility is commonly evaluated using overall task completion time, yet this aggregated measure may obscure phase-specific movement deficits and underlying kinematic control mechanisms. This study aimed to examine phase-specific temporal characteristics and trunk kinematic patterns during a continuous functional mobility task in a sample of very old adults (mean age, 87.95 years).

Twenty-one older adults (87.95 ± 2.60 years) performed a timed up and go-based task consisting of standing up, walking, turning, returning, and sitting down. Trunk kinematics were recorded using a wearable inertial measurement unit to capture tri-axial accelerations and trunk orientation angles in the sagittal, frontal, and transverse planes. The task was segmented into six phases. Temporal parameters and trunk kinematic variables were analyzed using Pearson correlation analysis.

Overall task completion time was strongly correlated with the standing-up phase (r = 0.743, p < 0.01) and the walking-after-turn phase (r = 0.782, p < 0.01). During standing up, vertical trunk acceleration was positively associated with mediolateral acceleration (r = 0.561, p < 0.01). Trunk orientation measures were positively correlated across planes during standing up, whereas sagittal and transverse plane angles were highly correlated during sitting down (r = 0.951, p < 0.01).

In this small sample with a mean age of approximately 88 years, phase-specific durations and trunk kinematic measures showed descriptive patterns of association. The results are hypothesis-generating and do not establish causal mechanisms, fall prediction, or superiority over total TUG time. Replication with repeated measurements and a larger, well-characterized sample is needed.