Peering Under the Hood of Africa's
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 masteryIn
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 Keino's 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
Kenya's Rift Valley, from a group of tribes called the Kalenjin who
number little more than 3 million people.
abound about what Kenya-born writer and runner John Manners calls
"the greatest geographical concentration of achievement in the
annals of sport." 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?
Kenya's Kip Keino in 1972.
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 the world's fastest
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, Saltin's group began comparing Kenyan and
Scandinavian runners by scrutinizing their physiological makeups and
assessing the "trainability" of novice runners in both countries.
A decade later, the scientists have ruled out most of the popular
explanations for Kenyans' domination of running. Altitude is not the
key to the riddle, they have found, because there's 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: "In spite of the diet, they perform at high
level." The running-to-school hypothesis was demolished as well:
Kenyan children aren't 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 Saltin's group that Kenyan runners squeeze
about 10% more mileage from the same oxygen intake than Europeans
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 "birdlike legs,
very long levers that are very, very thin [on which they] bounce and
Saltin's 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%, Saltin's
team calculates. For the Kenyans, that translates into an 8% energy
savings to run a kilometer. "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 on the Kenyan question. But "I
think Saltin is probably the most correct that anyone is at the
moment," says physiologist Kathryn Myburgh of the University of
Stellenbosch in South Africa, who is exploring the role of Kenyans'
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 "extraordinarily high" capacity for fatty acid
oxidation, which helps wring more energy out of the muscles'
biochemical reactions. Because intense training alters the body's
biochemistry, Saltin says that he can't say for sure whether the
ezyme levels are due to genes or training. But he adds, "Ithink it's
| Triumph of fast twitch. Carl
Lewis, a U.S. sprinter with West African roots, winning the
400-meter race at the 1992 Olympics in Barcelona.
Research in South Africa jibes with the Copenhagen group's
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
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 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. 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, "the purest measure
of running speed," says Entine, whose book set off a broad debate on
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.
differences don't 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
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 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.
| Out of East Africa.
In less than 2 decades, Kenyans came to dominate
the top 20 performances in six races ranging from 800 meters
to the marathon.
CREDIT: HENRIK B. LARSEN, J. COMP.
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 "with elevated levels of
what it takes to perform anaerobically at very high power output,"
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
| Road Test. Masks monitored
Kenyans' oxygen use.
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. Bouchard's 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 haven't spotted any
running genes yet.
There are a couple of intriguing possibilities, though. In 1999,
a team headed by Kathryn North of the Children's 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 gene--which results in
poorer energy conversion--in 18% of the members of a group of
Caucasians. In 2003, North's group reported in the American
Journal of Human Genetics 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 "forceful contractions at
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 Kenyans' 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 "living legends" 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. "At the moment
there is no evidence" 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,
"Differences 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."
Next month's Olympic games in Athens should demonstrate yet again
that West African runners are built for speed and Kenyans built to