Longitudinal associations of objectively measured physical activity and sedentary time with leg muscle strength, balance and falls in middle-aged women.

We examined the longitudinal associations of accelerometer-measured physical activity and sedentary time with leg muscle strength (LMS), balance, and falls in middle-aged women. This was a 5-year cohort study among 308 women aged 36-56 years. We used linear mixed-effects models to examine associations of baseline and change in accelerometer-measured sedentary time, light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA) with baseline and 5-year change in LMS and balance (timed up and go test [TUG], functional reach test [FRT], lateral reach test [LRT], and step test [ST]), and negative binomial/Poisson and log-binomial regression as appropriate to assess associations with falls after 5-year follow-up. Greater baseline MVPA was associated with better baseline LMS (β = 4.65 kg/SD, 95% CI: 1.37, 7.93) and TUG (β = -0.09 s/SD, 95% CI: -0.18, -0.01) but not with change in them over 5 years. Baseline MVPA was not associated with FRT at baseline but associated with a greater decrease in FRT (β = -0.87 cm/SD, 95% CI: -1.57, -0.17). Increased MVPA over 5 years was associated with less deterioration in FRT (β = 0.88 cm/SD, 95% CI: 0.14, 1.61). Increased sedentary time over 5 years was associated with a larger decrease in FRT (β = -0.82 cm/SD, 95% CI: -1.58, -0.07). Higher baseline LPA was associated with higher falls risk (IRR = 1.27, 95% CI: 1.02, 1.57). Higher baseline MVPA may benefit LMS and balance, while increasing MVPA in the medium term has little effect on change in these outcomes in mid-life. Detrimental association of LPA with falls may be due to greater exposures to environmental hazards.HighlightsOur study for the first time examined the longitudinal associations of objectively measured physical activity and sedentary time with leg muscle strength, balance and falls in middle-aged women.Higher baseline moderate-to-vigorous physical activity (MVPA) may be beneficial for muscle strength and balance at baseline but increasing MVPA in the medium term has little effect on change in LMS or balance outcomes in middle-aged women.Higher baseline light physical activity (LPA) was associated with an increased risk of falls.The detrimental association of LPA with falls may be due to a greater exposure to environmental hazards in midlife, which needs to be clarified in future research.