Energy costs of light activities in lean and obese adults

Recent studies of the role of physical activity in weight regulation have differed dramatically with regard to the treatment of the data. Although it has long been assumed that the energy cost of a physical activity is proportional to body weight, little data exists for light activities. We measured the energy costs above resting metabolic rate for 5 activities requiring less than 2.5 metabolic equivalents (METS), including sitting with arm or leg movement, standing with arm movement, carpet vacuuming and sit/stand/move about a small enclosure in 17 healthy young adults (weight=55-182 kg). Body composition was measured by bioelectrical impedance (%fat=7-53%). Energy costs for individual activities were linearly correlated with body weight (r=0.72-0.91) and fat-tree mass (r=0.830.93), but less well correlated with body mass index (r=0.59-0.82) and fat mass (r= 0.53-0.80). Intercepts using body weight as the independent variable were small, but slightly positive (0.1-0.26 kcal/min) except for vacuuming (0.65 kcal/min). Results were similar for fat-free mass, except for vacuuming and sit/stand/move, which had negative intercepts (-0.37 and 0.52 kcal/min, respectively). These results support the assumption that energy costs of light physical activities are related to body weight, but also support the use of fat-free mass as a covariant for comparison of energy costs of light activities between individuals.