Your butt on chairs: How chairs shaped human physiology

Have you ever thought about how odd it is that we’re the only species on Earth that uses a tool for sitting? Think about it. When your dog or cat needs to sit, she just…sits. But before you can sit, you need to grab an assistive device. What?

Of course, we can sit on the ground if we want to–so why don’t we?

What did people do before chairs?

Old bushwoman, Kalahari, Botswana, Africa

Well, as you might have guessed, we did not always have chairs. Instead, we squatted. I mean, we probably sat on the ground, too–and rocks, and logs. But the squatting position would be useful when the ground was muddy, or full of creepy-crawlies. Also, sometimes the ground is COLD! The “resting squat” was likely a major component of daily life in pre-agricultural times, and remains so today in many cultures, particularly in the East (Sheridan 2020, Hewes 1955).

Most Westerners (specifically, adult Westerners) do not find this position to be very comfortable to hold for long periods of time; but if you grow up doing it, your hip, knee ankle joints become well-adapted to this position, and it is quite comfortable.

You see, during fetal development, grooves called squatting facets are formed on your tibia and talus where they meet to form your ankle joint (Sheridan 2020).

Images: Satinoff 1972

These grooves allow the foot to hyper-flex to help the fetus fit better inside the uterus (Dlamini and Morris 2005; Garg et al. 2015). It may also be a vestigial structure, originating in a time when it was necessary for an infant to be able to grip its mother’s fur with its toes while clinging close to her.


This ability to flex the ankle joint at a very acute angle positions the squatter’s center of gravity directly over your feet, creating a stable resting position. It also allows the person to rest on their own legs, with the back of their thighs resting on their calves such that most of their muscles can relax, engaging only slightly to maintain balance (Mays 1998).

Notice the acute angle at which the foot is flexed, and how this man is able to rest his thighs on the back of his own legs.


You may have noticed that small children, especially toddlers, often use a resting squat to examine a toy or object that is close to the ground.

The squatting position is also used throughout the world to facilitate defecation (Sikirov 2003; Sakakibara et al. 2010), as well as childbirth. And it might be something to try; a review by the Cochrane Collaboration concluded that use of the squatting position during the pushing stage of labor was associated with a reduction of the duration of the second stage, as well as reductions in other complications associated with decreases in the length of the pushing stage, perception of pain, need for assisted delivery, and hemorrhage (Gupta, 1999, Nilsen et al. 2011).

Enter: the chair

But, use it or loose it. The squatting facets fade away if you don’t continue to engage in habitual squatting. The bone remodels, the Achilles tendon tightens, and the ankle joint becomes less flexible (Barnett, 1954 Sertinoff 1972).

Behold, THE KLISMOS


The earliest evidence of chair use comes from the sculpture of a chair from the Cycladic islands in the Aegean Sea, dated to between 2,800 and 2,700 B.C. For the next few thousand years, sitting on something a proper chair, such as the Greek klismos, was largely for the wealthy elite. Everyone else sat on stools, which were low to the ground and still supported a squat-like posture. Habitual squatting continued to be used for toileting until the 19th century, but even today flushing squat toilets are widely used outside of the West.

In the archaeological records, the bone markers that indicate habitual squatting are commonplace until a steady decline begins around the end of the Middle Ages (Boulle 2001; Sertinoff 1972). 

Sedentary lifestyle

Sedentary trends began with the advent of agriculture and have been particularly pronounced since World War II (Dundes 1987). The period from the 1950’s onward has, in the West, been marked by a steadily increasing number of daily hours spent sitting in chairs. Reclining in a chair isn’t just different from a squat posturally. In a squat, core, leg, and foot muscles are slightly engaged to maintain balance. A chair requires much less core engagement.

Extensive amounts of time sitting in chairs has been well documented to be associated with increased noncommunicable diseases such as heart disease, diabetes, and cancer, largely through decreased energy use and insufficient cardiovascular conditioning (Owen 2008; Katzmarzyk et al. 2009). One study even found an increased risk of all-cause mortality associated with sitting for hours on end every day as is done in the West (Dunstan 2010).

man on office chair with back pain

But what about the effects on the skeletal system, and growth and development? Knee issues and back pain are a combined result of sustained sedentary posture placing disproportionate stress on certain structures in the body. But also, these things are affected indirectly by weight gain that results from the use of fewer calories. In other words, our knees and backs are very unintelligently designed, and gravity is the enemy of upright-walking apes who love bacon cheese steakburgers. (As I write this I am shifting in my seat in attempt to relieve my iliotibial band syndrome!)

Another interesting area to look is the pelvis, which facilitates the birth of babies. A 2012 comparative study conducted by the National Institutes of Health found that that a sample of 98,359 mothers who gave birth between 2002 and 2008 labored for a median of 2.6 hours longer (first time moms) and 2.0 hours longer (experienced moms) than a sample of 39,491 who delivered between 1959 and 1966 (Laughon et al. 2011). The results remained significant even when the authors controlled for factors known to affect length of labor, such as maternal age and obesity. Recent trends towards longer and sometimes more difficult labor may, in part, be influenced by trends towards an increasingly sedentary lifestyle, where a large percentage of daily life spent sitting in chairs can lead to weak pelvic floor muscles. Since it is known that a weak pelvic floor is associated with less-than-ideal positioning of the fetus for birth (Phillips and Monga, 2004), habitual squatting may contribute to optimal positioning of the fetus for birth, as may running by way of pulling the coxxyx (tailbone) back, and thus widening the pelvic outlet. Moreover, strength and tension in the pelvic floor muscles help provide control and traction during the pushing stage of labor.

Weak pelvic floor muscles are also known to contribute to prolapse of the uterus and bladder and urinary incontinence that sometimes precipitate from childbirth (Hagen and Stark 2013). Exercises that involve squatting and a generally more active lifestyle strengthen the pelvic floor muscles and assist in the retention of normal organ positioning, much in the way that a more active lifestyle would make use of the gluteal muscles.

So should I get a standing desk or what?

I mean, if you want. It is important to remember that biological imperatives are not moral imperatives, so you should do what you want with your body! But, one of the things that this evolutionary perspective does for us is tell us that the statue-like lifestyle we live today is just not what our bodies are adapted for, and that if we want our bodies to continue to work well in the long run, it might be a good idea to work with our biology as much as we can, not against it. Contrary to popular beliefs, though, we didn’t evolve to be persistence runners, and standing desks haven’t been shown to make much of a difference. The key variable, here, seems to be movement. You don’t need to hit the gym 6 times a week or run a 10k in order to reap the benefits of movement. Just, you know…move! More and more research is supporting the idea that being active can help maintain a healthy cardiovascular system and increase lifespan.

Sources:

Barnett C.H. “Squatting Facets on the European Talus.” Journal of Anatomy 88.4 (1954): 509-13.

Boulle, Eve-Line. “Evolution of Two Human Skeletal Markers of the Squatting Position: A Diachronic Study from Antiquity to the Modern Age.” American Journal of Physical Anthropology 115.1 (2001): 50-56.

Dundes, Lauren. “The Evolution of Maternal Birthing Position.” American Journal of Public Health 77.5 (1987): 636-41.

Dunstan et al. “Television Viewing Time and Mortality: The Australian Diabetes, Obesity and Lifestyle Study (AusDiab)” Circulation. 2010;121:384-391.

Gardosi, J., Noreen Hutson, and Chris B-Lynch. “Randomised, Controlled Trial Of Squatting In The Second Stage Of Labour.” The Lancet 334.8654 (1989): 74-77.

Hagen, Suzanne, and Diane Stark. “Conservative Prevention and Management of Pelvic Organ Prolapse in Women.” The Cochrane Library 7.12 (2011). Cochrane Database of Systematic Reviews.

Hewes, Gordon W. “World Distribution of Certain Postural Habits.” American Anthropologist 57.2 (1955): 231-44.

Katzmarzyk, Peter T., Timothy S. Church, Cora L. Craig, and Claude Bouchard. “Sitting Time and Mortality from All Causes, Cardiovascular Disease, and Cancer.” Medicine & Science in Sports & Exercise 41.5 (2009): 998-1005.

Laughon, S. Katherine, D. Ware Branch, Julie Beaver, and Jun Zhang. “Changes in Labor Patterns over 50 Years.” American Journal of Obstetrics & Gynecology 206.5 (2012): 419.

Nilsen, Evenise, Hugo Sabatino, and Maria Helena Baena de Moraes Lopes. “The pain and behavior of women during labor and the different positions for childbirth.” Revista da Escola de Enfermagem da USP 45.3 (2011): 557-565.

Owen, N., A. Bauman, and W. Brown. “Too Much Sitting: A Novel and Important Predictor of Chronic Disease Risk?” British Journal of Sports Medicine 43.2 (2008): 81-83.

Sakakibara, Ryuji, Kuniko Tsunoyama, Hiroyasu Hosoi, Osamu Takahashi, Megumi Sugiyama, Masahiko Kishi, Emina Ogawa, Hitoshi Terada, Tomoyuki Uchiyama, and Tomonori Yamanishi. “Influence of Body Position on Defecation in Humans.” LUTS: Lower Urinary Tract Symptoms 2.1 (2010): 16-21.

Sertinoff, Merton I. “Study of the Squatting Facets of the Talus and Tibia in Ancient Egyptians.” Journal of Human Evolution 1.2 (1972): 209-10.

Sheridan, Susan Guise. “Pious Pain: Repetitive Motion Disorders from Excessive Genuflection at a Byzantine Jerusalem Monastery.” Purposeful Pain: The Bioarchaeology of Intentional Suffering. Springer Nature Swizerland, 2020.

Wells, Jonathan C.K., Jeremy M. DeSilva, and Jay T. Stock. “The Obstetric Dilemma: An Ancient Game of Russian Roulette, or a Variable Dilemma Sensitive to Ecology?” Yearbook Of Physical Anthropology 55 (2012): 40-71.