Physical activity in confined conditions as an indicator of free-living physical activity

The main determinants of daily energy expenditure are body size and physical activity. Activity energy expenditure is the most variable component of total energy expenditure. It was assessed whether the physical activity level in confined conditions is an indicator of free-living physical activity.

Activity energy expenditure was measured over 1 day in a confined environment of a respiration chamber (floor space, 7.0 m(2)), where activities were restricted to low-intensity activities of daily living, and over 2 weeks in a free-living environment using doubly labeled water. Subjects were 16 women and 29 men (age, 31 +/- 10 years; BMI, 24.2 +/- 2.7 kg/m(2)).

The free-living activity level of the subjects, as a multiple of resting energy expenditure, was 1.76 +/- 0.13. Activity energy expenditure in the chamber was 47 +/- 13% of the value in daily life, and the two values were correlated (r = 0.50, p < 0.001; partial correlation corrected for age, gender, and BMI: 0.40, p < 0.01). The chamber value explained 25% of the total variance in free-living activity energy expenditure.

The activity level of a subject under sedentary conditions is an indicator of activity energy expenditure in daily life, showing the importance of nonexercise activity for daily energy expenditure.