Research Shows That They Burn Little Energy and Bob Around Less Than Westerners : African Women Use Heads and Graceful Skill to Bear Burdens

NAIROBI, Kenya —  One of Africa’s most arresting sights is that of a woman walking demurely down a dirt road with what looks like a neck-wrenching load on her head.

In Ghana, women glide through Accra’s central market with such improbable burdens on their heads as a cage full of live chickens, a card table piled with glassware, a 100-pair-high stack of blue jeans.

In southern Sudan, Dinka women walk for miles with only a ring of palm fronds padding their shaved skulls from the weight of 80-pound clay pots brimming with sorghum beer.

Here in Nairobi, girls skip home from school, holding hands with each other, bundles of books on their heads.

Ease Is Not Illusory

As remarkable as the loads themselves, and the fact that they rarely fall off, is the seeming ease with which African women carry them.

That ease is more than seeming, according to researchers in biomechanics. It is real.

A study here found that African women can carry up to 20% of their body weight on their heads without increasing their rate of energy consumption.

The study was conducted at the University of Nairobi, and the findings published early this year in Nature, a leading British science journal.

It shows that a 130-pound African woman can walk with a 26-pound load on her head and burn up no more energy than if she were carrying nothing at all. The load, in effect, moves for free.

Male Researcher Failed

But it doesn’t work for everyone. Harvard physiologist Norman C. Heglund, one of the five experts on animal and human locomotion who worked on the study here, tried his head.

Like the Kenyan women in the test, he loaded a bag of sand on his head, put on a gas mask to gauge his oxygen consumption and mounted a motorized treadmill.

He found that the more sand he carried, whether on his head or in a pack on his back, the more energy he burned. Two other control carriers, a man and a woman who had not grown up carrying things on their heads, also consumed more energy as they carried more weight.

Besides besting a Harvard expert in biomechanics, African women are far more efficient carriers of loads than are army recruits. Studies of recruits with 75-pound packs on their backs found that they have sharply higher rates of energy consumption than African women with similar loads on their heads.

While these African women burn no energy whatever in toting 20% of their body weight atop their heads, recruits with similar loads on their backs increased their energy consumption by 13%.

Lessons for U.S. Army

All this has not escaped the U.S. government. Heglund says U.S. Army researchers from Washington called him last summer for his thoughts on how the African women do it.

Heglund speculates that the women, who begin carrying what he called “pretty darn decent loads at the age of 12,” have made physiological adaptations to carrying the weight.

He also speculates that they have developed balancing techniques that allow them to carry their loads smoothly. Non-jerky locomotion, Heglund says, wastes little energy.

African women, as it turns out, have little energy to waste. According to a recent United Nations report, women do about 70% of the farm work on this continent.

Rural women often work 14- to 16-hour days. At the beginning and end of the daily routine, an African woman fetches wood and water. These loads usually are carried home on her head.

Bone Support Suggested

“It could be that they have adapted their spines to support the loads through bones rather than with muscles,” said Heglund, who holds engineering and biology posts at Harvard.

Arguing for the bone-support theory, Heglund said, is the research finding here that African women can stand quietly with up to 70% of their body weight on their heads with no measurable effect on their energy consumption. This means a 130-pound African woman can stand around with 91 pounds on her head with “no metabolic cost.”

“For a Westerner to consider carrying 70% of his body weight on his head is inconceivable,” Heglund continued.

Besides the possibility of bone support through adaptation, Heglund and his fellow researchers suspect that African women--through long practice--have devised an energy-efficient method of movement that keeps the loads on their heads from bobbing around.

“The primary work of walking is that your center of mass goes up and down,” Heglund said. He speculated that the load on an African woman’s head may not go up and down as on the head of an “untrained” person.

Back, With Instruments

Heglund plans to return to Kenya this month to resume head-carrying research with University of Nairobi physiologist Geoffrey Maloiy, who led the original experiments here.

He will bring along an accelerometer, a device that measures up-and-down and back-and-forth movement. The accelerometer will be attached to the loads when the women go on the treadmill.

One practical result of the research, Heglund suggested, is that it may be possible to devise spring-loaded, special-suspension backpacks that could ease the work of soldiers or hikers.

To work properly, the backpacks would have to convert the jerky walk of a soldier into the smooth movements of an African woman.