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Source: http://www.irishnews.com/lifestyle/2020/03/12/news/squatting-or-kneeling-better-for-health-than-sitting-scientists-claim-1862901/

12th March 2020

RESTING postures such as squatting or kneeling may be better for health because require more muscle activity than sitting on a chair, researchers claim.

The findings are based on data gathered from a hunter-gatherer population in Tanzania who wore devices that measured physical activity as well as periods of rest.

Anthropologists from the US found that despite being sedentary for almost 10 hours each day, equivalent to clocking a shift in the office at the desk, the Hazda people appeared to lack the markers of chronic diseases associated with long periods of sitting.

They believe this is down to the "active rest postures" used by the tribe.

Dr David Raichlen, a professor of biological sciences at the University of Southern California and lead author on the study, said: "One of the key differences we noticed is that the Hadza are often resting in postures that require their muscles to maintain light levels of activity – either in a squat or kneeling."

Prolonged sitting has been linked to an increased risk of cardiovascular disease and death, but according to the researchers, this contradicts the evolutionary aspect which favours strategies that conserve energy.

Brian Wood, an anthropologist at the University of California, said: "Preferences or behaviours that conserve energy have been key to our species' evolutionary success. But when environments change rapidly, these same preferences can lead to less optimal outcomes. Prolonged sitting is one example."

The researchers found that their test subjects had high levels of physical activity for just over an hour a day alongside several hours of inactivity, between nine to 10 hours a day.

But despite remaining in resting postures for long periods of time, the Hazda people did not show any signs of the health conditions associated with a sedentary lifestyle.

The researchers said is because the Hazda squatting and kneeling uses more muscle movement than sitting on a chair.

 

Sitting, squatting, and the evolutionary biology of human inactivity

David A. RaichlenHerman PontzerTheodore W. ZdericJacob A. HarrisAudax Z. P. MabullaMarc T. Hamilton, and Brian M. Wood
 
  1. Edited by C. Owen Lovejoy, Kent State University, Kent, OH, and approved January 27, 2020 (received for review July 12, 2019)

 
 

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Significance

Inactivity is a growing public health risk in industrialized societies, leading some to suggest that our bodies did not evolve to be sedentary. Here, we show that, in a group of hunter-gatherers, time spent sedentary is similar to that found in industrialized populations. However, sedentary time in hunter-gatherers is often spent in postures like squatting that lead to higher levels of muscle activity than chair sitting. Thus, we suggest human physiology likely evolved in a context that included substantial inactivity, but increased muscle activity during sedentary time, suggesting an inactivity mismatch with the more common chair-sitting postures found in contemporary urban populations.

Abstract

Recent work suggests human physiology is not well adapted to prolonged periods of inactivity, with time spent sitting increasing cardiovascular disease and mortality risk. Health risks from sitting are generally linked with reduced levels of muscle contractions in chair-sitting postures and associated reductions in muscle metabolism. These inactivity-associated health risks are somewhat paradoxical, since evolutionary pressures tend to favor energy-minimizing strategies, including rest. Here, we examined inactivity in a hunter-gatherer population (the Hadza of Tanzania) to understand how sedentary behaviors occur in a nonindustrial economic context more typical of humans’ evolutionary history. We tested the hypothesis that nonambulatory rest in hunter-gatherers involves increased muscle activity that is different from chair-sitting sedentary postures used in industrialized populations. Using a combination of objectively measured inactivity from thigh-worn accelerometers, observational data, and electromygraphic data, we show that hunter-gatherers have high levels of total nonambulatory time (mean ± SD = 9.90 ± 2.36 h/d), similar to those found in industrialized populations. However, nonambulatory time in Hadza adults often occurs in postures like squatting, and we show that these “active rest” postures require higher levels of lower limb muscle activity than chair sitting. Based on our results, we introduce the Inactivity Mismatch Hypothesis and propose that human physiology is likely adapted to more consistently active muscles derived from both physical activity and from nonambulatory postures with higher levels of muscle contraction. Interventions built on this model may help reduce the negative health impacts of inactivity in industrialized populations.

Footnotes

  • Author contributions: D.A.R., H.P., A.Z.P.M., M.T.H., and B.M.W. designed research; D.A.R., H.P., J.A.H., and B.M.W. performed research; D.A.R., H.P., T.W.Z., J.A.H., M.T.H., and B.M.W. contributed new reagents/analytic tools; D.A.R., H.P., T.W.Z., M.T.H., and B.M.W. analyzed data; and D.A.R., H.P., T.W.Z., J.A.H., A.Z.P.M., M.T.H., and B.M.W. wrote the paper.

  • The authors declare no competing interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.1911868117/-/DCSupplemental.

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