Trends in spontaneous physical activity and energy expenditure among adults in a respiratory chamber, 1985 to 2005.

Abstract

Fidgeting, a type of spontaneous physical activity (SPA), has substantial thermogenic potential. This research aims to examine secular trends in SPA and energy expenditure (EE) inside a respiratory chamber. From 1985 to 2005, healthy adults (n=678; mean age: 28.8 years; men: 60%; 522 Indigenous American, 129 White, and 27 Black) had a 24-hour stay in the respiratory chamber equipped with radar sensors. Body composition, glucose tolerance, fasting insulin, insulin action (hyperinsulinemic-euglycemic clamp), and insulin secretion (intravenous glucose tolerance test) were measured as covariates. SPA, adjusted for age, sex, race, and body composition, declined (r=-0.30, p<0.0001), with a concomitant rise in the energy cost of SPA (r=0.30, p<0.0001). The 24-hour EE adjusted for covariates increased (r=0.31, p<0.0001), which was reflected in increases in EE during sleep (r=0.18, p<0.0001) and during the awake, fed condition (r=0.28, p<0.0001). The secular trends in SPA or 24-hour EE were unchanged with adjustment for measures related to glucose metabolism. Secular trend analyses showed a decline in fidgeting. However, this decline in SPA was partially counterbalanced by an increase in energy cost of this activity and a rise in EE. Nevertheless, our results support public health efforts to promote small but sustained changes in these behaviors.