Body composition is associated with physical activity in daily life as measured using a triaxial accelerometer in both men and women

Background: Activity-related energy expenditure is the most variable component of total energy expenditure and thus an important determinant of energy balance. Objective: To determine whether body composition is related to physical activity in both men and women. Design: A total of 134 healthy participants were recruited (80 women, 54 men; aged 21 +/- 2 years; body mass index, 22.0 +/- 2.4). Physical activity was measured for a period of 2 weeks using a triaxial accelerometer for movement registration (Tracmor). Percentage body fat (% BF) was determined by underwater weighing and deuterium dilution according to Siri's three-compartment model. Results: The participant characteristics-body mass, height and gender together explained a substantial part of the variation in % BF (R-2 = 0.75, SEE = 4.0%). Adding physical activity to the model increased the explained variation in % BF with 4% (R-2 = 0.79, SEE = 3.7%, P < 0.001). Taking seasonality into account by adding the number of daylight hours as an independent variable further increased the explained variation with 1% (R-2 = 0.80, SEE = 3.7%, P < 0.05). In analogy, the association was evaluated for both genders separately. In women, % BF and physical activity were significantly associated (P < 0.001). In men, % BF was only associated with physical activity when seasonality was taken into account as well (P < 0.05). This probably resulted from men participating more in season bound sports, because an association was found without adjusting for seasonality when only men with a consistent year-round participation in sports were considered. Conclusion: Evidence was found for an association between body composition and physical activity in both genders. A consistent year-round degree of physical activity appears to be a prerequisite to reveal the association. Moreover, Tracmor-assessed physical activity improves the estimate of % BF when a participant's characteristics are taken into account.