Quantifying energy expenditure and physical activity in the context of dose response.

PURPOSE Methods for assessing physical activity (PA) and energy expenditure (EE) were reviewed to identify potential limitations to evaluating and interpreting dose-response relationships between PA and health-related outcomes and to suggest future research directions in this area. METHODS Literature describing PA and EE assessment methodology was reviewed according to the reported validity, reliability, and feasibility of the measurement in epidemiologic studies. A summary of this review is presented for techniques applicable to studying PA or EE among free-living individuals. RESULTS Several methods with varying degrees of precision and feasibility have been used to assess PA and EE in free-living populations. Lack of a gold standard field measure of PA may explain some of the variability in precision among these methods. The most accurate field measure of EE appears to be doubly labeled water; however, this approach has limited feasibility in terms of cost and use in studies of total EE only. Electronic motion sensors and physiologic measures related with EE are limited in their ability to discriminate specific types of PA and by inconvenient measurement procedures. Self-reported PA records and surveys are low-cost, relatively unobtrusive methods of assessing PA and EE in field settings and vary in terms of their format, mode of administration, and degree of detailing habitual PA levels. Disparity in the metric used to quantify PA and EE exists within the current literature, which limits the interpretation and comparison of observed dose-response relationships. CONCLUSIONS Efforts to develop equated methods of assessing PA and EE in free-living populations are needed before a systematic evaluation and interpretation of dose-response characteristics between PA and specific health-related parameters can be undertaken.