Background: With aging, daily physical activity (PA) becomes less frequent and more fragmented. Accumulation patterns of daily PAincluding transitions from active-to-sedentary behaviors-may provide important insights into functional status in older, less active populations. Methods: Participants of the Baltimore Longitudinal Study of Aging (n = 680, 50% male, aged 27-94 years) completed a clinical assessment and wore an Actiheart accelerometer. Transitions between active and sedentary states were modeled as a probability (Active-to-Sedentary Transition Probability [ASTP]) defined as the reciprocal of the average PA bout duration. Cross-sectional associations between ASTP and gait speed (m/s), fatigability (rating-of-perceived-exertion [RPE]), 400 m time (seconds), and expanded short physical performance battery score were modeled using linear and logistic regression, adjusted for chronic conditions. Further analyses explored the utility of ASTP over-andabove total daily PA. Results: In continuous models, each 0.10-unit higher ASTP was associated slower gait (β = −0.06 m/s, SE = 0.01), higher fatigability (β = 0.60 RPE, SE = 0.12), slower 400 m time (β = 16.31 s, SE = 2.70), and lower functioning (β = −0.13 expanded short physical performance battery score, SE = 0.03; p < .001). In categorical analyses, those in the highest tertile of ASTP were >2 times more likely to have high fatigability (rating of perceived exertion ≥10), slow 400 m time (>300 seconds) and reduced functional performance (expanded short physical performance battery score < 3.07) than those in the lowest tertile (p < .01). Further analyses demonstrated ASTP provided additional insight into functional outcomes beyond total daily PA. Conclusion: Fragmented daily PA-as measured by ASTP-is strongly linked with measures of health and functional status and may identify those at risk of high fatigability and reduced functional performance over and above traditional PA metrics.

To assess exposure of polyfluoroalkyl compounds (PFCs) among children, we measured the concentrations of perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonic acid, and 8 other PFCs in 24 pooled serum samples. The individual serum samples used to make the pools were collected from U.S. children who were participants in the 2001-2002 National Health and Nutrition Examination Survey. These children were from three major races/ethnicities (non-Hispanic blacks, non-Hispanic whites, and Mexican Americans), two age categories (3-5 and 6-11 years), and both sexes. PFCs were extracted from 100 microL of serum using online solid-phase extraction coupled to isotope dilution high performance liquid chromatography tandem mass spectrometry; detection limits ranged from 0.1 to 0.4 ng/mL In the final ANOVA models, race was the only significant demographic factor, and concentrations appeared to be lower for Mexican Americans than for the other two racial groups. For example, for Mexican American children 6-11 years old, the least-squares means (LSM) estimates were 30.45 ng/mL (PFOS) and 6.125 ng/mL (PFOA), while for non-Hispanic white children of the same age group, the LSM estimates were 42.45 ng/mL (PFOS) and 7.575 ng/mL (PFOA). However, after adjusting for the potential underestimation of variance associated with the sampling design, race did not remain a significantfactor. Nevertheless,these findings suggestthat human exposure to PFCs among the population groups of children examined may differ and stress the importance of identifying the environmental sources and routes of exposure to PFCs.

Key PointsQuestionIs the manner in which older adults accumulate physical activity throughout the day, beyond the total amount of physical activity, associated with their mortality risk?FindingsIn this cohort study of 548 well-functioning adults aged 65 years and older, more fragmentated physical activity, but not total daily activity, was associated with increased mortality risk.MeaningFragmented physical activity of bouts lasting less than 5 minutes may reveal compensatory changes resulting from impaired physical function and may be associated with increased mortality risk.