These lines of evidence suggest that other factors that influence [resting metabolic rate], among them [physical activity], might also be responsible for the observed secular trend in [body temperature].'.
The study finds that the average American has seen their resting metabolic rate decline by six percent since 1820.The level of 'moderate to vigorous' physical activity has declined by approximately 27 minutes per day during the time period as well.
'The researchers figured that falling body temperature and falling physical activity are related and could be linked by the human metabolism, which produces body heat and is, in part, powered by what people are doing in terms of physical activity,' the statement addedAdditional factors outside of lower physical activity can reduce a person's RMR and body temperature, adding complications to a person's estimate