Objective Assessment of Activity, Energy Expenditure, and Functional Limitations in Older Men: The Osteoporotic Fractures in Men Study

Approximately 20% of U.S. adults aged 70 and older report at least some difficulty in activities of daily living (ADLs) or instrumental ADLs (IADLs) (1). While the proportion of older persons reporting a disability may be decreasing over time (2), the size of the population aged more than 65 years continues to increase and will reach 88.5 million by 2050 (3), resulting in a significant number of persons at risk of becoming disabled and unable to care for themselves. Many studies have demonstrated that physical activity is associated with several health benefits, including a reduced risk of all-cause mortality and disability (4–8). However, most of these studies have used self-reported questionnaire data that are only modestly associated with objective measurements of total energy expenditure (9,10). In addition, self-reported activity questionnaires generally gather information regarding specific and predetermined types of activity performed (such as sports, housework, and walking), which are subject recall and other biases that are likely influenced by participant characteristics. On the other hand, objective monitors record data in real time that are then processed to estimate broad types of activity and energy expenditure. Thus, questionnaire and objective assessment of activity are measuring different factors, and objective activity monitors more accurately estimate total energy expenditure. Little is known about the relation between the key measures and activity monitors, namely, total energy expenditure and time spent at various activity levels, with health and functional status. Accordingly, we used data from the Osteoporotic Fractures in Men (MrOS) study to determine whether objectively measured total energy expenditure, time spent in moderate or greater activity, or time spent in sedentary behavior was associated with the risk of self-reported functional limitations in older men.