The Goldilocks Days: optimising the older adults' time-use to prevent obesity, low fitness, risk and fear of falling.

This study introduces the concept of the "Goldilocks Day" – the optimal 24-hour time-use of intensity- or posture-specific composition specifically tailored for young (65–70 years) and old (> 70 years) older adults. We aimed (1) to optimal 24-hour time-use of compositions for each health outcome, and (2) identify the 'Goldilock Day' for all outcomes together. This approach, involving backwards pivot coordinates (bpcs), we provide a clearer interpretation of physical behavior data, offering practical insights for healthy aging. Data were collected from 309 older adults (65 + years) in Czechia, using accelerometers worn. Both intensity-specific (sedentary behavior - SB, light physical activity - LPA, moderate-to-vigorous physical activity - MVPA, and sleep) and posture-specific behaviors (lying, sitting, standing, moving, and walking) were assessed. Health outcomes included BMI, fall risk, fear of falling, physical fitness, usual gait speed, and lower extremity strength. Compositional regression models, based on the bpcs, were used to assess the relationships between time-use and these outcomes. In younger older adults, the time-use composition for optimal BMI included 7.5 hours of sleep, 12.0 hours of SB, 3.2 hours of LPA, and 1.4 hours of MVPA. Old older adults displayed slightly lower MVPA (1.0 hour) and increased SB (12.8 hours). Generally, higher MVPA and lower SB were associated with better physical fitness and reduced fear of falling. The optimal "Goldilocks Day" for both age groups highlighted the benefits of higher physical activity and reduced sedentary time, with significant implications for personalized health recommendations and improved health outcomes in Czech older adults.