Physical Activity and Total Daily Energy Expenditure in Older US Adults: Constrained versus Additive Models.

PURPOSE To examine the shape of the relationship between physical activity (PA) and total energy expenditure (TEE) and to explore the role of energy balance status (negative, stable, positive) in influencing this association. METHODS Cross-sectional. Participants were 584 older adults (50-74 yrs.) participating in the Interactive Diet and Activity Tracking in AARP study. TEE was assessed by doubly labeled water and PA by accelerometer. The relationship between PA and TEE was assessed visually and using non-linear methods (restricted cubic splines). Percent weight change (>3%) over a six-month period was used as a proxy measurement of energy balance status. RESULTS TEE generally increased with increasing deciles of PA averaging 2354 (SD = 351) kcal/d in the bottom decile to 2693 (SD = 480) kcal/d in the top decile. Cubic spline models showed an approximate linear association between PA and TEE (linear relation p < 0.0001, curvature p = 0.920). Results were similar in subgroup analyses for individuals classified as stable or positive energy balance. For those in negative energy balance, TEE was generally flat with increasing deciles of PA averaging 2428 (SD = 285) kcal/d in the bottom decile to 2372 (SD = 560) kcal/d in the top decile. CONCLUSION Energy balance status appears to play an important role in the relationship between PA and TEE. When in a positive energy balance, the relationship between TEE and PA was consistent with an additive model, however, when energy balance was negative, TEE appears to be consistent with a constrained model. These findings support PA for weight gain prevention by increasing TEE; however, the effect of PA on TEE during periods of weight loss may be limited. An adequately powered, prospective study is warranted to confirm these exploratory findings.