Because of its established links with endurance-performance capacity,2 the ACE gene is certainly the most widely studied strip of genetic material in elite runners and other high-level athletes. One might expect the I allele of this gene to be considered prize DNA, the right genetic stuff for elite runners, but research does not support this idea.
In a study carried out with 76 elite Ethiopian endurance runners whose competitive distances ranged from 5K to the marathon, the distribution of ACE genotypes (II, ID, and DD) was not significantly different from that found in 410 nonelite Ethiopian endurance athletes, 38 sprint and power athletes from Ethiopian national teams, and 317 sedentary Ethiopian controls.7 From the standpoint of the performance-promoting ACE gene, the Ethiopian elites were just like everyone else (see following discussion of ACE gene frequencies in elite Kenyan runners).
Scientists have not been able to pinpoint a genetic difference in elite endurance runners that predicts success.
Dave Thompson/PA Archive/Press Association Images
Myth of the Genetic Edge in East Africans
In spite of the tenuous connection between genetic makeup and elite-athlete status, there is a widespread perception that elite East African endurance runners enjoy a kind of genetic advantage over sedentary individuals around the world and also over non–East African elites. This conception has been put forth on scientifically based websites and in the popular press.8
According to this thinking, elite Kenyan and Ethiopian runners have specific genes or optimal combinations of genetic material that promote superior running performances and are a fundamental cause of these runners’ success. These high-performance genes and genetic complexes are supposedly absent in non-African runners or perhaps are present in much lower frequencies. The hypothesis is that Kenyan and Ethiopian endurance-running supremacy can be explained primarily by genetic differences between African and Caucasian runners as opposed to training disparities or dissimilar cultural factors.
As noted in chapter 1, a finding that appears to support this genetic hypothesis is that the world’s best runners do not come from all parts of Kenya and Ethiopia but rather seem to emerge from discrete geographic regions and specific, somewhat small subpopulations within those two countries.9, 10 In Kenya a disproportionate number of international elite runners have grown up in the rural areas and are members of the Kalenjin tribe; as many as 70 percent of Kenyan elites are Kalenjin, even though Kalenjins make up just 4 percent of the total Kenyan population. In western Kenya, Kalenjins do not marry freely with members of other tribes, and as noted in chapter 1, the existence of small, somewhat isolated populations of people can lead to genetic drift, which may cause certain variants of genes, including those related to performance, to increase dramatically in frequency.11 If such genetic variants, or alleles, have a major impact on endurance-running capacity, the subpopulations may produce unusually high numbers of outstanding endurance runners.
This line of thinking is not without its perils. Research reveals, for example, that the top runners within the East African subpopulations that have produced an unusual number of world-class athletes are those individuals who have simply run the farthest to school.9, 10 When running is the form of basic transportation, baseline maximal aerobic capacity (O2max) is about 30 percent higher than when little running is done when going from place to place.12 The endurance platform from which these runners begin their careers may be loftier from the outset in East African athletes. What appears to be a genetically based phenomenon might rather be, at least partially, the outcome of an extremely high level of childhood activity.
Contentions about the genetic superiority of Africans when it comes to athletic endeavors are not confined to distance running. The stars of the 2008 Beijing Olympics were clearly Usain Bolt, a black Jamaican sprinter, and Michael Phelps, a white swimmer from the United States. Post-Olympic discussions of Bolt’s amazing success were focused primarily on his presumed genetic advantage, even though very little is known about the genes and gene combinations that are linked with top-level sprinting.13 In contrast, the commentary about Phelps centered on his diet and incredible training habits; genetic hypothesizing was completely absent.14 Scientific support for the idea that elite runners of African descent have an exceptional genetic profile is minimal. Propositions about genetic advantages for these runners as compared to Caucasians thus appear to have little or no scientific basis.
Research on the ACE Gene
As described in chapter 2, one of the best-known performance genes is the strip of genetic material that codes for the angiotensin-converting enzyme, or ACE; this gene is found on chromosome 17 in the human genome and has been linked with improved running economy and heightened endurance.15 The I allele of this gene, when present on both members of the chromosome 17 pair, leads to lower circulating concentrations of ACE, decreased ACE tissue activity, increased endurance performance.16-21 and superior average running speed during an intense 30-minute effort.16 Possession of the D allele has been linked with higher maximal running velocity16 and the attainment of elite-level sprint and anaerobic performances.22, 23 Thus, one might expect elite endurance runners to have an unusually high frequency of the I allele.
To determine whether superior endurance runners are more likely than others to have the I allele on chromosome 17, researchers from the International Centre for East African Running Science (ICEARS) at the University of Glasgow took DNA samples from 221 national-level Kenyan runners, 70 international Kenyan competitors, and 85 individuals drawn at random from the Kenyan population.24 The Glasgow investigators also assessed genetic composition at a site known as A22982GD that has been closely linked with ACE levels in subjects of African descent as compared with Caucasians.
The ICEARS scientists found absolutely no association between running performance and I allele frequency or A22982GD status among the Kenyan subjects. Contradicting the idea that elite runners enjoy a genetic edge, the findings indicated that elite and national-level Kenyan runners were not more likely to carry the I allele or A22982GD when compared with the Kenyan population at large. A separate study also found no association between I allele frequency and being an elite endurance athlete.25 Finally, there is also no evidence that Kenyan runners have a higher frequency of the I allele compared with Caucasian competitors.
Research on mtDNA and Haplogroups
Mitochondrial DNA (mtDNA) analysis has been used with elite Ethiopian distance runners to determine whether they are genetically distinct from the general population.26 Variations in mtDNA could have a significant effect on endurance performance because mtDNA codes for the creation of the enzymes necessary for oxidative phosphorylation (the use of oxygen to create the energy needed for muscular work) within muscle cells. MtDNA is inherited directly and entirely from mother to child and will change only if mutations in the mtDNA occur. An extremely interesting consequence is that linked complexes of mutations may occur in different branches of descent from a single female ancestor (the so-called mitochondrial Eve). Each branch of this tree is referred to as a haplogroup.
If superior mtDNA is a reason for the success of elite Ethiopian runners, such individuals should be confined to one specific branch of the tree. However, the mtDNA analysis revealed that the elite Ethiopians were scattered throughout the tree; they had a wide distribution of haplogroups that was similar to the general Ethiopian population.26 Surprisingly, some of the elite Ethiopian runners shared a recent, common mtDNA variant with many Europeans. The similarity of mtDNA between elite Ethiopians and Europeans negates the ideas that elite Ethiopians are a genetically distinct, isolated population and that unusual patterns of mtDNA could be responsible for their success.
The notion that elite African runners are not a genetically distinct group is further supported by research on Y chromosome haplogroups. The Y chromosome, present only in males, contains a small amount of genetic material that may have relevance for physical performance. Y chromosomes are passed from fathers to sons, with n
o maternal contribution, and thus haplogroups may arise that are the branches created from one so-called ancestral Adam. As is the case with mtDNA, mutations in Y chromosomes cause entirely different branches to sprout from the overall genetic tree. However, the research with Y chromosome haplogroups in Ethiopian runners has revealed that the elites have the same distribution of Y haplogroups found in the general population.27
An interesting aspect of this study of Ethiopian Y chromosome haplogroups is that some of the Y chromosome haplogroups were present in significantly different frequencies in the elite runners compared with the population at large. As this book goes to press, frequencies of Y chromosome haplogroups in elite Kenyan runners are being studied. If the same specific Y chromosome haplogroups are found to be over- or underrepresented in elite Kenyan and elite Ethiopian runners, the obvious conclusion would be that the Y chromosome has a major impact on endurance-running performance in males, and that males who find themselves on the correct branch, or haplogroup, of the genetic tree have an inherent advantage over the endurance-running males on another branch. It should be noted, however, that there is currently no evidence that specific Y haplogroups are more common in elite African runners compared with relatively underachieving elite American or European runners.
Conclusion
The existing research indicates that elite African runners are not a genetically distinct group. It is highly unlikely that East Africa produces performance-optimizing genotypes that cannot be matched in other regions of the world. Overall, the hypothesis that the world’s best runners are genetically distinct from average athletes and even sedentary controls remains a very shaky and unproven proposition. In addition, elite athletes from non–East African countries have genetic constitutions that are very similar to the genetic makeups of nonelite athletes and sedentary individuals in those countries.
Part II
Biomechanics of Running
Chapter 4
The Body While Running
Emil Zatopek ran with the worst upper-bodyform imaginable: His head rolled from side to side, his torso tilted unpredictably, and he let out an earsplitting wheezing that earned him the nickname the “Czech Locomotive.” In spite of his seemingly dysfunctional form, the indomitable man from Koprivnice checkmated his opponents in four different Olympic competitions, bringing home a quartet of gold medals, including three from the 1952 Games alone.
When Tirunesh Dibaba runs, she appears to fly over the ground like a well-tuned jet plane, with silky-smooth movements of her appendages and an upper body always balanced and under control. Dibaba has two world records in her dossier, not to mention four world championships, three Olympic gold medals, and five world cross-country championships.
It would be impossible for the body movements of Zatopek and Dibaba during running to be any more different (see figure 4.1, a-b), and yet each athlete achieved a similar level of international success. Such a contradiction forces exercise scientists to examine how the body actually moves during running—and to investigate whether optimal motions can be identified.
Sport biomechanics—a discipline in which the laws of mechanics are employed in order to gain a greater understanding of athletic movement and performance—can help resolve such issues. The biomechanics of running is usually divided into two key components: kinetics and kinematics. Human kinetics, also called kinesiology or dynamics, is the study of the actions of external and internal forces on an individual’s body during movement, especially with regard to muscles, tendons, ligaments, and skeletal system. For running, kinetics can be described as the study of the forces and motions characteristic of the running gait. Human kinetics employs the sciences of biomechanics, anatomy, physiology, psychology, and neuroscience to understand how runners and other athletes move. For example, a kinesiologist might study the way in which the nervous system alters its control of the leg muscles in response to training or how force production by the hamstrings is changed after a program of hill work. The word kinetics comes from the Greek words kinesis (movement) and kinein (to move).
Figure 4.1 Kinematic analysis of successful runners like (a) Emil Zapotek and (b) Tirunesh Dibaba reveals significant disparities in running form.
PA Archive/Press Association Images
Rogan Thomson/Action Plus/Icon SMI
Kinematics is the branch of biomechanics that analyzes the body’s motion during running without taking into account the body’s mass or the various forces acting on it. This discipline includes the study of the movements and positions of muscles, joints, and various parts of the body such as the feet, legs, pelvic area (core), and torso. For example, kinematics is employed to study the timing and extent of pronation (inward rolling of the foot) and supination (outward rolling of the foot) during the stance phase of gait and also the magnitudes of hip, knee, and ankle flexion and extension during running.
Both approaches are extremely valuable. Kinematic analysis can be very useful for studying a runner’s form and ultimately improving it. Kinetics helps coaches and runners understand a broad range of important running phenomena including muscle actions in response to fatigue, the relative activities of various muscle groups as maximal running speed is improved, and the ways in which foot-strike pattern shapes work output by various muscles of the legs.
Kinematic View of Running Form
A kinematic approach reveals that running is a highly repetitive movement. About 85 to 95 times per minute, each leg passes through a stance phase, during which the foot is in contact with the ground, and a swing phase, during which the foot is free from the ground and the leg swings forward from the hip preparing for subsequent foot strike and initiation of another stance period. One gait cycle (figure 4.2, a-d) begins at the moment when a foot strikes the ground, continues through stance, progresses through swing, and ends when the foot hits the ground again.
Figure 4.2 A gait cycle begins when the foot (a) strikes the ground, (b) continues through stance, (c) swings, and (d) makes contact with the ground again.
Since running movements are so repeatable, they would appear to be well suited for optimization, the establishment of specific patterns of motion that would be relatively uniform among runners with similar training backgrounds and that would improve both performance and injury prevention.1 Many runners and coaches believe that there is a right way to run from a kinematic perspective—and a variety of wrong ways associated with poorer performances and an increased risk of injury.
Scientific research has struggled in its attempt to identify biomechanical optima, however, and endurance and middle-distance runners with similar training backgrounds and performances often display wide variation in kinematic variables. One study found that support time, the duration of time a foot spends on the ground during the stance phase of the gait cycle, averaged 179.9 milliseconds in a group of 54 elite female runners but varied considerably between runners: up to 6 percent quicker than average for some competitors and 7 percent longer than usual for others.1 This is a substantial difference: A runner with a support time of 170 milliseconds would spend 4 fewer seconds anchored to the ground for each 200 steps than would a runner with a support time of 190 milliseconds, a time that would produce a considerably higher velocity for the 170-millisecond athlete if stride length were relatively equal. Support time is a biomechanical variable intimately connected with stride rate—the briefer the support time, the faster the stride rate—and thus maximum running velocity; there is an expectation that support time would be quite uniform across runners of high competitive ability. Research rejects this hypothesis but does reveal that support time is quite malleable, with explosive training providing an important way of upgrading, or shortening, the stance phase of running gait and boosting maximal speed.
Similarly, the extent of knee flexion during the swing phase of gait should be a factor linked with running performance. Reduced flexion straightens the legs during the swing phase and thus expands the length of the leg lever (see figure 4.3). A lever is simply a rigi
d object that moves about a fixed point, or fulcrum. In the case of a human runner involved in the swing phase of gait, the leg is the rigid object and the hip is the fulcrum. The beauty and advantage of levers is that a heavy object, such as the leg and its attached foot, can be moved relatively easily by applying a relatively small force near the fulcrum. However, the force required to move the leg increases as the leg straightens and lengthens and thus a highly flexed knee should be most economical during swing. It saves energy because less force is required to pull the leg forward.
Somewhat surprisingly, though, maximal knee flexion varies considerably among elite runners of comparable ability: The average maximal flexion is 127.9 degrees, but the observed range in maximal flexion is from approximately 109 to 140 degrees.1 Knee-flexion angle is measured between the shin and an imaginary straight line that runs straight down the thigh and through the knee. When the leg is fully extended and perfectly straight at the knee, knee-flexion angle is 0 degrees.
Figure 4.3 Knee flexion during the swing phase of the gait cycle is linked with economical movement and superior performance.
These studies reveal that there is wide variation in kinematic variables among runners, even in well-trained elite competitors. One purpose of carrying out such research is to determine how kinematic variables influence performance. If a kinematic study determines that a decrease in duration of stance is linked with improved running economy and faster 5K performances, for example, researchers can then explore the factors and training modes that reduce stance time. Kinematic variables respond to training, and thus to the development of muscular strength and neural coordination, although they are also dependent on individual characteristics such as skeletal structure, flexibility, joint stiffness, and muscle length.
Running Science Page 5