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Updated: Oct 15, 2025
Infrared Thermography for the Detection of Changes in Brown Adipose Tissue Activity
Published on: September 28, 2022
Historical body temperature records as a population-level 'thermometer' of physical activity in the United States
Andrew K Yegian1, Steven B Heymsfield1, Daniel E Lieberman1
1Department of Human Evolutionary Biology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA.
Abstract:
Over the past two centuries profound technological and social changes have reduced overall levels of physical activity (PA). However, just how much population-level PA levels have declined since the Industrial Revolution is unknown because methods for measuring PA, such as accelerometry and the doubly labeled water technique, were developed only within the last few decades. Here, we show that historical records of resting body temperature (TB) can serve as a 'thermometer' of population-level PA, enabling us to use the well-documented secular decline in TB in the US1 to approximate PA decline in the US since 1820. Using cross-sectional data relating TB to resting metabolic rate (RMR) and RMR to PA, we estimate that RMR has declined by ∼6% and moderate to vigorous PA by ∼27 minutes per day since 1820 in the US.
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