Using Heart Rate and Accelerometry to Define Quantity and Intensity of Physical Activity in Older Adults.

Background: Physical activity (PA) prevents disease and promotes longevity; yet, few older adults meet the recommended daily guidelines. Wearable PA and heart rate monitors provide the opportunity to define age-related differences in the absolute and relative intensity of daily activities, and provide insight into the underlying factors influencing PA in older adults.
Methods: Participants in the Baltimore Longitudinal Study of Aging (n = 440, 52% male, aged 31 to 88 years) completed a clinical assessment and wore an Actiheart monitor in the free-living environment. The association between age and minutes per day in sedentary, light, moderate, and vigorous PA was assessed using relative intensity, as defined by heart rate reserve, and absolute intensity using activity count thresholds.
Results: In cross-sectional analyses, time spent in sedentary and light activities as defined by relative intensity did not differ across age (p > 0.05), whereas time spent in moderate and vigorous relative PA was higher for each 1 year increase in age (p < .01). Using absolute intensity PA thresholds, older adults registered fewer activity counts per day with more sedentary time and lesser amounts of light, moderate, and vigorous PA (p < .05). Persons with higher relative and lower absolute PA intensity had poorer functional performance and higher subclinical disease indicators. Conclusions: These findings suggest that time spent in moderate or higher intensity activities may not be lower with age after considering changes in physiology, functional ability, and subclinical disease burden and highlight the need for more age- and ability-specific PA research to inform future interventions and public health guidelines.