Movement and Energy Expenditure in Obesity

The authors quantitated the movement and energy expenditure of 20 healthy self-proclaimed “coach potatoes.” Ten lean (BMI = 23 ± 2 kg/m²) and 10 modestly obese (BMI = 33 ± 2 kg/m²) volunteers donned and wore a physical activity monitoring system (PAMS) for 10 days while continuing their normal occupations, hobbies, and day-time and night-time activities, and while consuming a diet designed to maintain a constant body weight. Energy expenditure related to purposeful exercise and that related to routine activities of daily living, non-exercise activity thermogenesis (NEAT), was determined. NEAT was further divided into energy expended in relation to posture (lying, sitting, standing) and energy utilized for movement (ambulation). The findings revealed that both groups slept (lying) for similar intervals, but that obese subjects sat 164 minutes per day longer and stood 152 minutes less per day than did control volunteers (Figure). This translated into a mean lower daily energy expenditure of 352 kcal. Neither supervised weight loss (8 kg) in 7 obese subjects nor weight gain (4 kg) in 10 lean volunteers altered the distribution times of posture and movement, suggesting that these activities were “intrinsic” to the individual rather than environmentally determined.¹ However, the mechanism(s) that regulates posture and movement distribution are not known. The investigators suggest that if an obese subject were to increase daily caloric expenditure by 350 kcal (without corresponding increase in calorie intake, of course), over the course of 1 year there would be a 15 kg weight loss!

The components of daily energy expenditure are depicted (above) and the differences between lean and obese subjects are shown (right). The pie charts show the cost of unplanned physical activity (NEAT).

Editor’s Comment: It has long been known by clinical observation that very obese subjects move imperceptibly when sitting (ie, they do not fidget) and choose to sit when others in the vicinity are standing; by inference they must be conserving every calorie. However, present data provide quantitative proof on this propensity even in only modestly obese individuals. The method for measurement of PAMS was designed by Levine and consisted of 6 sets of sensors embedded in special underwear, 4 “inclinometers” attached to the trunk and thighs, and 2 “triaxial accelerometers” fixed to the base of the spine.² Each subject wore this unit 23:45 hours daily (15 minutes for showering) for 10 days. These instruments recorded data every half-second providing information on body position and motion 1 728 000 times over 10 days per subject! Experimentally, injection of orexin into the paraventricular nucleus of rats increases NEAT, implying that posture and movement may be modulated by neural transmitters. Clearly, efforts to increase NEAT in our obese patients are worthwhile—primarily by substituting physical activity such as walking for television viewing and game playing.


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