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How they spend their inactive time is different from in industrialized societies.


Images of three young men squatting.

Enlarge / These positions are commonly seen when Hadza individuals are inactive.

People have taken various measures to keep from being sedentary, including activity monitors, standing desks, and smartphones and watches that prod us to get out of our chairs. All of that effort is based on a growing body of studies indicating that too much time seated is associated with a variety of health risks. Other work has suggested that it takes very little time out of our seats to ensure better health.

It’s a somewhat odd set of findings, given that many other mammals have lifestyles optimized for sloth (including, obviously, the sloth). That has led to the idea that humanity’s recent evolutionary history—one in which we spent millions of years as hunter-gatherers—has optimized us for an active lifestyle. The sedentary lifestyle of developed economies isn’t bad for us in itself; instead, it simply represents a mismatch to our metabolism.

But is there any evidence that this is the case? A group of researchers have worked with some modern hunter-gatherers and found that the answer is both yes and no. While the hunter-gatherers are even more sedentary than those in an industrialized nation, they tend to spend more of that time squatting and kneeling—activities that involve more muscle activity than sitting in a chair.

Fitbit meets the Hadza

How do you find out how hunter-gatherers spend their time? In the case of the new research, you ask them to wear an activity tracker. Twenty-eight members of Tanzania’s Hadza people agreed to wear the device for a bit over a week, during which time they gathered about 97 percent of the food they ate from the surroundings, mixing small and large game with berries and tubers. Afterward, software was used to track their activity at 15 second intervals.

The big surprise of the study: there really wasn’t that much activity. The typical Hadza adult spent nearly 10 of their waking hours without having any detectable motion. That’s more than the Netherlands and US, which are closer to nine hours, and over a full hour more of sedentary time than the average Australian. The Hadza had, on average, somewhat longer stretches of inactivity and made more transitions between upright and resting than Europeans, but there was a lot of variation among individuals, so these latter differences weren’t statistically significant.

There are, however, two big differences between the hunter-gatherers and those in industrialized societies. The first is that when they’re active, the Hadza typically are very active, easily exceeding the US recommendations for physical activity per day. The second is how the Hadza spend their time when they’re not active.

The researchers set up cameras where the Hadza were living and took hourly images during waking hours. These were used to determine what those wearing activity trackers were doing while at rest. If they were inactive, their posture was registered.

It was very rare to see any of the Hadza sitting on a log or rock as if it were a chair; instead, roughly half their time was spent sitting on flat ground. But they also spent time in positions that are rare in industrialized societies: kneeling and squatting. These two positions added up to over a third of the Hadza’s sedentary time. The researchers used electrodes to track the muscle activity in the legs of individuals while they were in these positions and found that they involved more muscle work than simply sitting in a chair.

The big picture

These positions don’t involve as much muscle activity as walking; they’re closer to a more active form of sitting. Still, the authors hypothesize that this may help explain some of the measures of heart health, which are better in the Hadza than they are in industrialized societies.

While that’s plausible, there’s a number of reasons to be skeptical of the bigger picture here. With the vast majority of their food coming from the surrounding countryside, the Hadza are going to have a very different diet than those in industrialized countries. And as noted above, the Hadza tend to be more active as well. Both of these could contribute significantly to the better indications of heart health seen in the Hadza.

The other issue is whether the indications of reduced heart health seen in sedentary industrialized societies can be attributed to a mismatch between our activity and our evolutionary history. Heart issues tend to become problems later in life, and estimates are that most hunter-gatherers simply don’t live to the sort of age where heart health becomes a problem. There very well may be other health benefits that could be seen earlier in life, and those could be the subject of evolutionary selection. But the researchers involved in this study don’t test any of them.

Still, the research provides a potentially useful contribution to the discussion about how best to limit the effects of a sedentary lifestyle. It suggests that there may be more to it than simply a lack of activity. And if the results can be confirmed in additional hunter-gatherer populations, maybe we’ll ultimately see some squatting desks appear on the market.

PNAS, 2020. DOI: 10.1073/pnas.1911868117 (About DOIs).

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