Comparing Physical Activity Levels and Metabolic Quotients to Quantify the Physical Activity Transition in Rwanda

Although humans used to be physically active hunter-gatherers and subsistence farmers, there has been a recent and ongoing global physical activity transition as billions of people adopt industrial lifestyles primarily in urban areas. In order to analyze how to quantify the magnitude of this physical activity transition in a natural experiment, we compared two different metrics of physical activity metabolism among intensive subsistence farmers in northern Rwanda (Burera District, Northern Province) and urban professionals in the country's main city, Kigali.

We used the doubly labeled water (DLW) method to measure body composition, daily energy expenditure, and estimate activity energy expenditure in 36 individuals (n = 19 rural, n = 17 urban). We then used two metrics to compare activity energetics between the groups: Physical Activity Level (PAL), the ratio of total to resting energy expenditure, and Activity Metabolic Quotients (AMQ), a size-normalized measure of the daily metabolic demand from physical activity.

While PALs suggest that Rwandan farmers are 1.5 times more active than urban office workers on average (PAL: 2.41 vs. 1.56), AMQs indicate that the rural farmers actually spend 2.6 times more energy on physical activity than urban office workers (AMQ: 1.85 ± 0.09 vs. 0.72 ± 0.05, p < 0.0001).

Metrics based on total daily metabolism such as PAL and TMQ captured some of the differences in physical activity metabolism between the farmers and office workers but severely underestimated the magnitude of the difference as illustrated by AMQ. We find that rural Rwandan farmers have some of the highest physical activity metabolic rates ever measured in humans, emphasizing the magnitude of the physical activity transition and suggesting that subsistence farming can demand much higher energy expenditures compared not just to industrial lifestyles but also to hunting and gathering.