Carrying the Load: A Weighty Matter
Marcie Myers had been studying the way women carry loads for a decade when a student collaborator made an illuminating observation: load bearing is both physical and psychological work. In an instant, Myers saw her research from a fresh vantage.
Throughout the world, women from developing cultures spend much of their day encumbered by heavy loads — from food to toddlers — doing work that supports the whole clan. Life is not that different in the developed world. “Think of the women you know,” suggests Myers, co-chair of St. Kate’s biology department and research director of the Women’s Health Integrative Research (WHIR) Center. “How many of them carry both the literal and metaphorical loads for their families?”
The loads we carry and the way we carry and think about them is a product of our evolutionary history. This work plays an important role in our health, our sense of purpose and even our longevity. It’s written in our bones — and shapes our psyches. Based on research looking disproportionately at men, a currently popular idea is that humans evolved to run. By contrast, the work of Myers and her collaborators has shown that the form and physiology of modern women was most likely shaped by thousands of years of carrying heavy loads for long distances.
“It’s untenable that women carrying kids, food and fuel for the whole gang, were running out and about in the hot sun,” says Myers. Women’s bodies have adapted to accommodate the loads they need to carry, and those changes — from reproductive hormones to social networks — have impacted human evolution.
“A couple of million years ago, our human ancestors began migrating throughout the world,” Myers explains. “We simply would not have made it out of Africa if women were not good at carrying loads. We carried the food; we carried the water. By definition we carry the offspring.”
And there are evolutionary reasons why the carrying is best done slowly. The more a load carried on the back weighs in relation to a woman’s size, the farther forward she will lean while walking to compensate. The more intense an activity, the higher a woman’s heat load, the more her hormones suppress her fertility. This is good if the load she is carrying is a pregnancy, nursing baby or child who cannot walk with the group, but potentially problematic to her society.
“When our early human ancestors moved from place to place, the whole group had to move at the pace suited to load-carrying females,” says Myers. “If they walked too fast the women would have overheated and then not reproduced enough to maintain
Three KidCarry studies
In the 2010 study KidCarry I, Myers and a team of student researchers compared the way men and women carried Jordy, a 22-pound manikin designed with toddler proportions. In KidCarry II, they examined the impact load bearing had on women’s walking speed, which correlates directly to their reproductive need to discharge heat from their bodies. KidCarry III examined commercially available baby carriers.
After finishing the first study, Myers and her student collaborators — by then, all seniors — traveled to Ithaca, New York, to present to the National Council on Undergraduate Research.
Reviewing the data the night before, the team was still trying to explain a puzzling result: Even though loads slowed everyone down, when asked to walk at “comfortable” and “brisk” speeds, the women in the study chose faster speeds than the men. Never mind that the task of carrying the toddler model was a significantly harder task for the smaller women.
“’You know, this looks like a psychological thing,’” Anna Myhre ’12 ventured. In a culture that tells women going full tilt is a virtue, it made sense to her.
“It contradicted what we had thought,” Myhre recalls. “I thought the context had to be considered. These were contemporary women who probably felt a time pressure.”
To Myers, the implications were clear: “Anna’s insight helped us see the balanced strategy the women were using in choosing their speed. Loaded women were walking faster than loaded men because of their facility with carrying, but also because of their psychological propensity to just get things done.”
There is psychological literature tying the heaviness of the load a woman carries to the “weightiness” of her endeavors, Myers says. When factors force us to lighten our loads, we can struggle to retain a sense of purpose.
In Namibia, for example, women typically must spend precious time and calories carrying water home from distant sources. However, when cities installed water pumps to ease this burden, many of the women became depressed. They were no longer walking for hours in companionship with their female friends, doing important work for their families.
“So you fixed the water problem and released the women from one burden on their time and energy,” says Myers. “But what replaces the lost sense of community and a job well done?”
Following a talk Myers gave earlier this year, art history professor Amy Hamlin approached with a personal observation. As a graduate student, Hamlin enjoyed the gravitas the enormous art books she carried lent to her studies. But she still flinches at the physical burden.
“Amy made a brilliant connection, suggesting that young girls in traditional cultures might be helped to transition from carrying siblings, firewood and water to carrying books,” says Myers. “Still ‘weighty’ work, still in community.”
The Benefits of a Brisk Pace
In all humans, stores of calcium are directed to bones that are used to bear weight. So for postmenopausal women the task of carrying food, water and goods has a protective effect.
“Evolutionarily speaking, we think grandmothers helped their kids and grandkids thrive by ‘sharing the load’ in terms of carrying food and kids,” says Myers. “It’s one reason grandmas live so long after they stop having babies.”
Closer to home, she and her contemporaries have a ready example in their own aging mothers. Like their ancestors, modern women are trained neuromuscularly by carrying children, oversized handbags and backpacks to slow down. Yet the slower an older woman walks the greater her risk of falling and statistically the closer she is to dying.
Over a lifetime of carrying loads, our brains, bones, and muscles get tuned to a slower rate of walking” Myers explains. “Even when unencumbered, older women have trouble quickening their pace.”
In her role at St. Kate’s WHIR Center, Myers is exploring ways to encourage middle-aged and older women to set down their “loads” and take up the weighty work of recapturing the brisk pace that will protect their longevity and quality of life.
Backpacks and Back Pain
Research published in 2012 in the Archives of Disease in Childhood found that more than 60 percent of teens surveyed carry backpacks weighing more than 10 percent of their body weight; nearly one in five carry more than 15 percent.
The findings echo Myers’s research: People compensate for heavier backloads by leaning forward, at a tremendous cost to their health. One in four of the students reported suffering significant back pain.
Broadly speaking, KidCarry III made clear, the more evenly a load is distributed around the waist the less the bearer has to strain to carry it. Digital textbooks, advocated by the U.S. Department of Education, could lessen the load for students. So too could storing academic tomes and musical instruments at school.