The 85th Annual Meeting of the American Association of Physical Anthropologists (2016)


Sitting, squatting, and the evolution of human inactivity

DAVID A. RAICHLEN1, HERMAN PONTZER2,3, JACOB A. HARRIS4, THEODORE W. ZDERIC5, MARC T. HAMILTON5 and BRIAN M. WOOD6.

1School of Anthropology, University of Arizona, 2Department of Anthropology, Hunter College, 3New York Consortium for Evolutionary Primatology, 4Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, 5Texas Obesity Center, University of Houston, 6Department of Anthropology, Yale University

April 15, 2016 2:45, A 703/704 Add to calendar

The evolution of the genus Homo was marked by a shift towards a highly active lifestyle that included increased physical activity. Due to this evolutionary history, many suggest our bodies require aerobic exercise to prevent chronic diseases. However, a separate set of physiological changes occurs during inactivity and also leads to chronic diseases in sedentary populations. During periods of inactivity, Westerners generally sit in chairs, leading to a reduction in the muscle-activity-induced production of enzymes that hydrolyze lipids for energy, increasing cardiovascular disease (CVD) risk.

Here, we examined inactivity in a hunter-forager population, the Hadza of Tanzania, to better understand patterns of inactivity in a lifestyle similar to that of our ancestors. Using thigh-worn accelerometers (activPals), we found that Hadza subjects (n=28) engaged in similar amounts of sedentary time compared with Western subjects (mean=9.02±1.10 hrs/day). However, when inactive, subjects generally sat on the ground or rested in squatting postures. Using electromyography, we found that, compared with chair-sitting, these “active” rest postures require significantly higher levels of muscle activity in soleus (p<0.05) and tibialis anterior (p<0.05). We hypothesize that the use of resting postures that require low-level muscle activity leads to increased production of enzymes that hydrolyze lipids, and an associated reduction in CVD risk. Markings on fossil limb bones suggest these “active” resting postures are an ancient part of hominin behavior, and current CVD risk may be due in part to an inactivity mismatch, where styles of rest no longer resemble the patterns of inactivity used during human evolution.

This project was supported by NSF-BCS 1440867 (DAR), NSF-BCS 1440841 (HP), NSF-BCS 1440671 (BMW), and the L.S.B Leakey Foundation (BMW)