Insights into functional mobility in older adults from the instrumented timed up and go (iTUG): a retrospective study

: This retrospective study aimed to examine age-related differences in functional mobility across narrowly defined age groups of community-dwelling older adults using the instrumented Timed Up and Go (iTUG) test. Specifically, we sought to identify which iTUG subtasks and sensor-derived parameters showed the most pronounced differences across age strata and to characterize phase-specific temporal and kinematic features from 65 years onward using a single-sensor approach. We hypothesized that age-related differences would not affect all iTUG components uniformly, with walking and turning-related parameters showing clearer differences across age groups than trunk excursion measures. Data from 212 healthy adults aged over 65 years were retrospectively analyzed and stratified into four age groups. Functional mobility was assessed using a single lumbar-mounted inertial measurement unit (IMU) during the iTUG. Primary outcomes included total and sub-phase durations (sit-to-stand, walking, turning, stand-to-sit), turning velocities, and trunk flexion/extension angles during postural transitions. Between-group differences were assessed using MANOVA followed by Bonferroni-adjusted ANOVAs. A significant main effect of age group was found for iTUG parameters (p < 0.001, η2 = 0.13). Total duration and most sub-phase durations increased across age groups, whereas no significant age-group differences were observed in trunk flexion or extension angles. These findings indicate that temporal and velocity-based iTUG parameters, especially those related to walking and turning, showed clearer age-stratified differences than trunk angular measures. Overall, the study provides descriptive age-stratified data on phase-specific iTUG features in community-dwelling older adults and supports the value of subtask-level analysis for characterizing functional mobility beyond total TUG duration alone.