Measuring Physical Activity With Ageing

Abstract Background: The world-population is not only ageing but also obesity rates in the elderly are increasing. The role of physical activity in the physiology of ageing and pathophysiology of elderly obesity is poorly defined although it is believed that physical activity declines with ageing. Increased illness burden, functional impairment, reduced quality of life and mortality in the elderly are related to physical inactivity. Physical activity may be divided into exercise activity and non-exercise activity. Non- exercise activity is all the movement an individual undertakes that is not planned, intentional exercise. Likewise the energy expended in physical activity consists of energy expended in purposeful exercise and the energy expended in non-exercise activity thermogenesis (NEAT). Since most elderly individuals who live in developed countries engage in limited exercise, the majority of physical activity and energy expended in physical activity in the elderly will be through non-exercise activity and NEAT, respectively. Because of the variety of non-exercise activities that free-living humans undertake, it has been challenging to obtain accurate measurements of either the amount or energetic cost of human non-exercise activity. Aims: The aims of this thesis are first, to ask if lean elderly individuals have decreased NEAT compared to lean young individuals. Second, I want to validate, in an elderly population, the Physical Activity Monitoring System (PAMS) that measures NEAT. Third, I want to explore the components of non-exercise activity and NEAT in lean elderly individuals. Fourth I want to compare non-exercise activity and NEAT between obese elderly and lean elderly individuals. Finally, I ask how non-exercise activity and NEAT are different between obese elderly and obese young individuals. Methodology: 10 lean elderly (76 ± 5 years, 24 ± 2 kg/m2) and 8 obese elderly (73 ± 3 years, 33 ± 3 kg/m2) subjects, and 10 lean young (38 ± 10 years, 22 ± 2 kg/m2) and 8 obese young (38 ± 7 years, 34 ± 2 kg/m2) subjects were recruited. Subjects received weight maintenance meals for the duration of the study. Subjects wore the PAMS for a total of 10 consecutive days and during this period they also had doubly labeled water administered in order to determine their total daily energy expenditure. For the subsequent three days the subjects were admitted to the General Clinical Research Center, Mayo Clinic, to have metabolic assessments (including basal metabolic rate, activity energy expenditure and thermic effect of food) performed. Duplicate whole body dual energy X-ray absorptiometry scans were also performed to assess body composition. Results: All subject groups were matched for fat-free mass. The lean elderly had on average 6 kg more fat mass (p = 0.04) compared to the lean young subjects, and the obese elderly had on average 18 kg greater fat mass (p