Below Thermoneutrality, Changes in Activity Do Not Drive Changes in Total Daily Energy Expenditure between Groups of Mice

In this study we investigated the relationship between activity and energy expenditure (EE) in mice. By determining the relationship between activity and EE over a 24 hr period in an individual mouse, activity was calculated to account for 26.6% ± 1.1% of total EE at 30°C. However, when comparing across multiple mice, only 9.53% ± 1.1% of EE from activity appeared to be independent of other components involved in the thermogenic response, suggesting other metabolic processes may mask the contribution of activity to EE. In line with this concept, below thermoneutrality mice still expended a substantial amount of energy on activity; however, at 24°C, 20°C, or 5°C, no independent effect of EE from activity on total daily EE could be detected. Overall these results suggest that when studying mice at temperatures below thermoneutrality, activity is unlikely to explain differences in EE between groups of animals.