Science, July 30, 2004
Peering Under the Hood of Africaıs Runners
By Constance Holden
Kenyans dominate endurance running, and West Africans excel as sprinters.
With a physiological explanation in hand, researchers are now probing the
genetics of this geographic mastery In 1968, a Kenyan runner named Kip Keino
emerged as a shining star of the Mexico City summer Olympics, setting a
world record in the 1500-meter race. Year after year Keinoıs success has
been followed by equally dazzling feats by his compatriots: Kenyan men now
hold world records in the 3000-meter track race, the 15-, 20-, and
25-kilometer road races, the half-marathon, and the marathon. Kenyan men
have won 13 of the last 14 Boston marathons. Kenyan women are also rising
fast: They hold half of the top 10 marathon times and world records in 20-,
25-, and 30-km track races. What is even more remarkable is that most of
these athletes come from a small area in Kenyaıs Rift Valley, from a group
of tribes called the Kalenjin who number little more than 3 million people.
Theories abound about what Kenya-born writer and runner John Manners calls
³the greatest geographical concentration of achievement in the annals of
sport.² Is it the high altitude that fosters big lungs and efficient oxygen
use? Is it their maize-based diet? Or the fact that many children run to
school? A grueling training regimen, perhaps? Such questions have inspired a
handful of researchers to try to define the Kenyan magic. Meanwhile,
scientists are unraveling why athletes whose ancestors come from the other
side of the continent--West Africa--have emerged as theworldıs fastest
sprinters.
Fuel economy
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, Saltinıs group began comparing Kenyan and
Scandinavian runners by scrutinizing their physiological makeups and
assessing the ³trainability² of novice runners in both countries.
A decade later, the scientists have ruled out most of the popular
explanations for Kenyansı domination of running. Altitude is not the key to
the riddle, they have found,
because thereıs no difference between Kenyans and Scandinavians in their
capacity to consume oxygen. And the Kenyan diet is on the low side for
essential amino acids and some vitamins as well as fat, says Dirk
Christensen of the Copenhagen center: ³In spite of the diet, they perform at
high level.² The running-to-school hypothesis was demolished as well: Kenyan
children arenıt any more physically active than their Danish peers. Do
Kenyans try harder? The researchers found that the 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 longer.
Lactate, generated
by tired, oxygen- deprived muscles, accumulates more slowly in their blood.
Comparisons of lactate levels have suggested to Saltinıs group that Kenyan
runners squeeze about 10% more mileage from the same oxygen intake than
Europeans can.
Just as more aerodynamic cars get better gas mileage, the Kenyan build helps
explain their fuel efficiency. A recent British TV documentary described the
Kalenjin as possessing ³birdlike legs, very long levers that are very, very
thin [on which they]
bounce and skip² along.
Saltinıs group has quantified this observation. Compared with Danes, the
thinner calves of Kenyans have, on average, 400 grams less flesh in each
lower leg. The farther a weight is from the center of gravity, the more
energy it takes to move it. Fifty grams added to the ankle will increase
oxygen consumption by 1%, Saltinıs team calculates. For the Kenyans, that
translates into an 8% energy savings to run a kilometer. ³We have solved the
main problem,² declares Henrik Larsen of the Copenhagen center. ³Kenyans are
more efficient because it takes less energy to swing their limbs.² Other
scientists say the jury is still out on the Kenyan question. But ³I think
Saltin is probably the most correct that anyone is at the moment,² says
physiologist Kathryn Myburgh of the University of Stellenbosch in South
Africa, who is exploring the role of Kenyansı training.
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. Saltin says that this results in an
³extraordinarily high² capacity for fatty acid oxidation, which helps wring
more energy out of the musclesı biochemical reactions. Because intense
training alters the bodyıs biochemistry, Saltin says that he canıt say for
sure whether the ezyme levels are due to genes or training. But he adds, ³I
think itıs genetic.² Research in South Africa jibes with the Copenhagen
groupıs findings.
A team led by exercise physiologist Adele Weston of the University of
Sydney, Australia, compared black South Africans, whose running strengths
are similar to those of Kenyans, with white runners. The two groups had
similar VO2 max values--that is, when putting out maximum effort, they used
up the same amount of oxygen per kilogram of body weight per minute. But the
black runners were more efficient in their oxygen consumption, lasting on a
treadmill at maximum speed for twice as long as the whites. As with the
Kenyans, the black South African runners accumulated less lactate and had
higher levels of key muscle enzymes.
A little more twitchy
Whereas East Africans dominate long- distance running, West Africans have
surged to the fore in short-distance events. Little research has been done
on West Africans, but thereıs powerful circumstantial evidence for some
physical advantages, as presented by Jon Entine in his book ³Taboo: Why
Black Athletes Dominate Sports and Why Weıre Afraid to Talk About It.²
Athletes of primarily West African descent--which includes the majority of
U.S. blacks--hold all but six of the 500 best times in the 100-meter race,
³the purest measure of running speed,² says Entine, whose book set off a
broad debate on the subject.
Various studies have shown that West African athletes have denser bones,
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, thin, and tend to
weigh between 50 and 60 kilograms, whereas West African athletes are taller
and a good 30 kilograms heavier, says Timothy Noakes, a prominent exercise
physiologist and researcher at the University of Cape Town.
The differences donıt stop with body shape; there is also evidence of a
difference in the types of muscle fibers that predominate. Scientists have
divided skeletal muscles into two basic groups depending on their
contractile speed: type I, or slow-twitch muscles, and type II, fast-twitch
muscles. There are two kinds of the latter: type IIa, intermediate between
fast and slow; and type IIb, which are superfast-twitch. Endurance runners
tend to have mostly type I fibers, which have denser capillary networks and
are packed with more mitochondria. Sprinters, on the other hand, have mostly
type II fibers, which hold lots of sugar as well as enzymes that burn fuel
in the absence of oxygen. In the 1980s, Claude Bouchardıs team at Quebecıs
Laval University took needle biopsies from the thigh muscles of white French
Canadian and black West African students. They found that the Africans
averaged significantly more fast-twitch muscle fibers--67.5%--than the
French Canadians, who averaged 59%.
Endurance runners have up to 90% or more slow-twitch fibers, Saltin reports.
Bouchard, now at Louisiana State University in Baton Rouge, says his team
looked at two enzymes that are markers for oxidative metabolism and found
higher activity of both in the West Africans, meaning they could generate
more ATP, the energy currency of the cell, in the absence of oxygen. The
study suggests that in West Africa there may be a larger pool of people
³with elevated levels of what it takes to perform anaerobically at very high
power output,² says Bouchard.
Although training can transform superfast-twitch type IIb fibers into the
hybrid type IIa,
it is unlikely to cause slow- and fast-twitch fibers to exchange identities.
Myburgh says
there is evidence that, with extremely intensive long-distance training,
fast IIa fibers can change to slow type I fibers. So far, however, there is
no evidence that slow-twitch fibers can be turned into fast-twitch ones. As
an athlete puts on muscle mass through training, new fibers are not created,
but existing fibers become bigger.
Running ACEs
The differences in physique and muscle makeup that underlie the dominance of
Kenyan endurance runners and West African sprinters doubtless have a strong
genetic component. But researchers are only just getting off the starting
mark in the search for genes that influence running performance. Bouchardıs
group, for example, is collecting DNA samples from 400 runners and other top
endurance athletes from the United States and Europe, but he says they
havenıt spotted any running genes yet. There are a couple of intriguing
possibilities, though. In 1999, a team headed by Kathryn North of the
Childrenıs Hospital at Westmead in Australia described two versions of a
gene that affects production of -actinin-3, a protein found only in
fast-twitch muscles. They found the less efficient version of the genewhich
results in poorer energy conversion--in 18% of the members of a group of
Caucasians.
In 2003, Northıs group reported in the ³American Journal of Human Genetics²
that only 6% of a group of sprinters had the gene defect; 26% of endurance
runners had it. The authors surmise that -actinin-3 helps muscles generate
³forceful contractions at high velocity.²
Alejandro Lucia Mulas of the European University in Madrid is taking DNA
samples from Eritrean runners to explore another candidate: different
versions of the gene for angiotensin-converting enzyme (ACE). Lucia says the
less active version, or I allele, of this gene is associated with less
muscle, less fluid retention, and more relaxed blood vessels--which would
enhance oxygen uptake--and appears to be more prevalent in endurance
runners.
And in Scotland, sports physiologist Yannis Pitsiladis has launched a major
onslaught on the Kenyansı secrets with the International Centre for East
African Running Science. Headquartered at the University of Glasgow, the
virtual center will bring together research on demography, diet, and
socioeconomic factors as well as genes. Pitsiladis says he has spent the
last 3 years in East Africa collecting DNA samples from their ³living
legends² and now has DNA from 404 Kenyan and 113 Ethiopian athletes. His
team has found a higher prevalence of the I allele for the ACE enzyme in
male marathoners compared with men from the general Ethiopian population.
But Pitsiladis thinks his numbers may lack significance given the
variability of the trait in African populations. ³At the moment there is no
evidence² that East Africans have a genetic advantage in running, he says.
None of the data negate the importance of cultural habits and training. But
as Entine quotes anthropologist and sports science expert Robert Malina, who
is retired from Michigan State University, ³Differences among athletes of
elite caliber are so small that if you have an advantage that might be
genetically based ... it might be very, very significant.²
Next monthıs Olympic games in Athens should demonstrate yet again that West
African runners are built for speed and Kenyans built to endure.
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