zondag, augustus 01, 2004

Why Africa runs the world

Thursday, 29th July 2004 06.45pm

Kenyan men and women dominate the long-distance running scene, winning
many of the world records year after year. Their feats have inspired a
handful of researchers to try to define the Kenyan magic.
Meanwhile, scientists are unravelling why runners from the other side
the African continent are the world's premier sprinters.

Leading the charge in penetrating the Kenyan mystique has been Bengt
Saltin, a Swedish physiologist who heads the Copenhagen Muscle Research
Centre in Denmark. In the 1990s, Dr Saltin's group began comparing
Kenyan and Scandinavian runners by scrutinising their physiology and
"trainability" of novice runners.

A decade later, the scientists have ruled out most of the popular
explanations for Kenyans' domination of running. Altitude is not the
key, nor is the Kenyan diet. A hypothesis about running to school has
also been demolished. Kenyan children are no more physically active
their Danish peers. Do Kenyans try harder? Researchers found that Danes
actually pushed themselves harder on a treadmill test, reaching higher
maximum heart rates.

An important clue is the ability of Kenyans to resist fatigue. Lactate,
a substance generated by tired, oxygen-deprived muscles, accumulates
more slowly in their blood. Comparisons of lactate levels have
to Dr Saltin's group that Kenyan runners squeeze about 10 per cent more
mileage from the same oxygen intake than Europeans.

The Kenyan build also helps explain the runners' fuel efficiency.
Kenyans have thinner calves than Danes, which means on average they
400 grams less flesh in each lower leg. The farther a weight is from
centre of gravity, the more energy it takes to move it. Fifty grams
added to the ankle will increase oxygen consumption by 1 per cent, Dr
Saltin's team calculates. For a Kenyan running 1km, that translates
an energy saving of 8 per cent. "We have solved the main problem,"
declares Henrik Larsen of the Copenhagen center. "Kenyans are more
efficient because it takes less energy to swing their limbs."

Other scientists say the jury is still out. But "I think Saltin is
probably the most correct that anyone is at the moment," says Kathryn
Myburgh, a physiologist at the University of Stellenbosch in South

However, slim lower legs are not the whole story. Kenyan runners also
have a higher concentration of an enzyme in skeletal muscle that spurs
high lactate turnover and low lactate production. Dr Saltin says this
helps wring more energy out of the muscles' biochemical reactions.
Because intense training alters the body's biochemistry, Dr Saltin says
he cannot say whether the enzyme levels are due to genes or training.
But he says, "I think it's genetic."

Whereas east Africans dominate long-distance running, west Africans
surged to the fore in short-distance events. Little research has been
done on west Africans, but there's powerful circumstantial evidence for
some physical advantages, as presented by Jon Entine in his book Taboo:
Why Black Athletes Dominate Sports and Why We're Afraid to Talk About
It, which stirred wide public debate. Athletes of primarily west
descent hold all but six of the 500 best times in the 100m race.

Various studies have shown that west African athletes have denser
less body fat, narrower hips, thicker thighs, longer legs, and lighter
calves than whites. But the differences between east and west Africans
are even more striking. The fabled Kenyan runners are small and tend to
weigh between 50kg and 60kg, whereas west African athletes are taller
and a good 30kg heavier, says Timothy Noakes, an exercise physiologist
at the University of Cape Town.

There is also evidence of a difference in the types of muscle fibres
that predominate. Scientists have divided skeletal muscles into two
groups depending on their contractile speed: Type I, slow-twitch
muscles, and Type II, fast-twitch muscles. Endurance runners tend to
have mostly Type I fibres, while sprinters have mainly Type II fibres,
which hold lots of sugar as well as enzymes that burn fuel in the
absence of oxygen. In the 1980s, Claude Bouchard's team at Quebec's
Laval University took needle biopsies from the thigh muscles of white
French Canadian and black west African students. They found the
averaged significantly more fast-twitch muscle fibres - 67.5 per cent -
than the French Canadians, who averaged 59 per cent.

Researchers are only just starting the search for genes that influence
running performance. Dr Bouchard's group, for example, is collecting
samples from 400 runners and other top endurance athletes from the US
and Europe, but he says they have not yet spotted any running genes.

There are a couple of intriguing possibilities, though. In 1999 a team
headed by Kathryn North of the Children's Hospital in Sydney,
described two versions of a gene that affects production of
a protein found only in fast-twitch muscles. They found the less
efficient version of the gene in 18 per cent of a group of Caucasians.
In 2003, Prof North's group reported in the American Journal of Human
Genetics that only 6 per cent of a group of sprinters had the gene
defect; 26 per cent of endurance runners had it.

Other researchers are investigating the gene for angiotensin-converting
enzyme (ACE). The less active version of this gene is associated with
less muscle, less fluid retention and more relaxed blood vessels -
would enhance oxygen uptake - and appears to be more prevalent in
endurance runners.

None of the data negate the importance of cultural habits and training.
But as Robert Malina, an anthropologist and sports science expert,
retired from Michigan State University, observes, "Differences among
athletes of elite calibre in physique or the ability to fire muscle
fibres more efficiently - genetically influenced characteristics - are
quite small, but such variation might be very significant at high
of performance."

This article was provided by The American Association for the
Advancement of Science, and its journal Science www.aaas.org