While the valid measurement of physical activity is generally difficult, measurement in older adults is particularly challenging given the relatively low levels of both total activity and intensity of the activities in which they participate. Self-report has shown limited validity when compared to direct measures of energy expenditure such as doubly labeled water, and there may be particular issues of concern with this methodology in older populations (e.g. impaired cognition). For the assessment of current physical activity levels in older adults, objective monitoring may be particularly advantageous, and if proven valid, will aid in future studies attempting to delineate the associations between physical activity and health. The primary hypothesis of the proposed study is that multiple sensor physical activity monitors will have greater precision than self-report when compared to direct measures of physical activity energy expenditure (doubly labeled water and indirect calorimetry). Additionally, single sensor monitors, either alone or in combination with selected self-report items, will have greater precision than self-report alone. Men and women (n=60), aged 65 or older, will be enrolled in this study. During ten days of energy expenditure measurement via doubly labeled water, subjects will wear a pedometer, a uniaxial accelerometer, and a multiple sensor monitor (accelerometer, galvanic skin response, temperature), and complete three self-report questionnaires for the assessment of physical activity. Single and multiple sensor monitors will also be worn in conjunction with a 24-hour stay in a whole room calorimeter in a smaller sample (n=20) to more precisely evaluate their measurement properties. Correlation, limits of agreement, and regression analyses will be used to determine the validity of the measures either independently, or in combinations, compared to the physical activity energy expenditure measurements. The proposed study will give insight into the most precise and accurate method of measuring current energy expenditure due to physical activity among older adults. This methodology can then be incorporated into future studies examining the associations between doses of physical activity and various health outcomes. ? ?
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