Free-living sit-to-stand kinematics as an indicator of lower extremity physical function

Strength-demanding daily activities such as sit-to-stand (STS) transitions are essential for independent living among older adults. Measurement of STS transitions using advanced wearables offers a broader picture of physical activity and potentially indicate a future decline in physical functioning. This dissertation had three aims: first, to develop an open and universal algorithm that can detect and quantify the intensity of free-living STS transitions; second, to compare how free-living STS characteristics differ between age and sex groups and how they are associated with laboratory-based measurements; and third, to determine whether free-living STS characteristics could be an indicator of future decline in physical functioning among community-dwelling older adults. Data were drawn from three projects: the Active Ageing–Resilience and External Support as Modifiers of the Disablement Outcome (n = 1 021), which included baseline (n = 479), 1-year intervention (n = 86), and 4-year follow-up measurements (n = 340); the Leuven project (n = 63) and Finnish Retirement and Aging Finnish project (n = 188). The participants in the studies were community-dwelling older adults aged 60 to 90 years. Free-living STS characteristics were measured using an algorithm developed in this study that processes thigh-worn accelerometer data (from 3–7 days of continuous recording). The results showed that free-living STS transitions could be accurately detected, and intensity could be quantified using a single thigh-worn accelerometer. Free-living STS characteristics differed between age and sex groups. Men performed more and higher-velocity STS transitions than women. Free-living STS characteristics were associated with laboratory-based measurements, fear of falling, and stair negotiation problems. Older and low-functioning individuals appeared to perform free-living STS transitions at a higher percentage of their maximal capacity than younger and high-functioning individuals. In addition, free-living STS maximal angular velocity can predict future physical decline over a 4-year follow-up. The study findings suggest that daily strength-demanding activities may indicate the adequacy of lower extremity muscle strength and that STS characteristics may predict physical functioning decline among older adults.