Walking as a Contributor to Physical Activity in Healthy Older Adults: 2 Week Longitudinal Study Using Accelerometry and the Doubly Labeled Water Method

Background: Physical activity is recommended to promote healthy aging. Defining the importance of activities such as walking in achieving higher levels of physical activity might provide indications for interventions. Objective: To describe the importance of walking in achieving higher levels of physical activity in older adults. Methods: The study included 42 healthy subjects aged between 51 and 84 years ( mean body mass index 25.6 kg/m(2) [ SD 2.6]). Physical activity, walking, and nonwalking activity were monitored with an accelerometer for 2 weeks. Physical activity was quantified by accelerometer-derived activity counts. An algorithm based on template matching and signal power was developed to classify activity counts into nonwalking counts, short walk counts, and long walk counts. Additionally, in a subgroup of 31 subjects energy expenditure was measured using doubly labeled water to derive physical activity level ( PAL). Results: Subjects had a mean PAL of 1.84 ( SD 0.19, range 1.43-2.36). About 20% of the activity time ( 21% [ SD 8]) was spent walking, which accounted for about 40% of the total counts ( 43% [ SD 11]). Short bouts composed 83% ( SD 9) of walking time, providing 81% ( SD 11) of walking counts. A stepwise regression model to predict PAL included nonwalking counts and short walk counts, explaining 58% of the variance of PAL ( standard error of the estimate=0.12). Walking activities produced more counts per minute than nonwalking activities (