Heredity, genes and sports performance
Heredity, Genes And Sports Performance: Dad, mum and you - how much do your genes really influence your performances?
When Nick's friends asked him to take part in a casual Saturday afternoon game of soccer, he didn't realize that kicking a ball around on a muddy field would change his life. But as he chased after that damned ball, while his leg muscles cried out in pain and his lungs heaved like circus tents in a storm, Nick realized that his body had gone all to hell - after just a few short years of scoffing up thick slices of Yorkshire pudding and slugging down pints of ale each night after work.
And Nick was not the kind of fellow to do things by halves. Just as he had eaten, imbibed, and lazed around really earnestly over the years, he began his new, fitter life by training with the steadfastness of a monk. Flab fell from his abdomen, muscles burst from his buttocks, sinews sprouted from his thighs, and his lungs expanded and deflated in a more relaxed manner as he cruised through his daily runs.
Nick even began to enter races, and his 10-K times improved steadily. His first competition took 47 minutes, but soon he was at 46 minutes, then 45, made a big breakthrough to 42, and - after a year of hard training - broke the magical 40-minute barrier with a euphoric 39:55. Soon he was running in the 39s regularly, and he even surged through a sizzling 38:30 one beautiful autumn day.
What happened next?
But then, sadly, the improvements in performance stopped. Nick waited, and trained, and raced, and waited some more, but when not a single additional second dropped from his race times, he began to fiddle with his training, added more speed work, carried out hill repetitions, took up weight training, bought books about Olympic athletes, and even went to Kenya on holiday in hopes of adding some East-African speed to his legs. The result? He continued to run his races in his usual 38s and 39s. Nick began to face the hard truth - that he just wasn't going to improve any further.
Now, Nick had entertained thoughts of running 10 kilometres in 35 minutes, and - if the truth be told - he had even had a secret longing which grew stronger each time he set a new PB. His hope was that he might be one of the lucky ones - someone to watch out for at races, someone who could be an elite athlete and actually win prize money from the sport. Since all of those hopes were now dashed, Nick did the only thing he could do. He began to blame his mum and dad.
Poor old mum, hobbling down the street to the market, and dad, puffing on his blasted pipe and reading the paper at the fireside, why hadn't they given him more of the right stuff? Why hadn't mum done more training as a schoolgirl, taken up marathon running as a young woman, set age-group records after menopause, and encouraged Nick to be more active? Why hadn't dad chucked away his god-awful pipe? Surely that foul device had clogged Nick' s lungs with smoke as a child, thwarting his aerobic development.
A chip off a bad block?
Nick continued to resent his parents' poor influences for some time, but then one day at a race in London, Nick - for no apparent reason at all - decided to line up with the elite runners at the starting line. If he couldn't run a great 10K, he wanted to at least feel what it was like to rub shoulders with the great runners. As he stared at the slim bodies and determined faces next to him, he had a sudden realization: all of the parental training and coaching in the world would not have helped him. He was stuck in bad stock: his parents had simply not given him the genes of a Gebrselassie or a Kiptanui. In fact, Nick' s soul - the soul of a running fanatic - was trapped in the body of a greengrocer. Nick returned to the middle of the pack of runners with a horrible realization: great athletes are born - not made.
But was he right? Is it true that the most important thing an aspiring athlete can do is to choose the right parents, as the great Swedish exercise physiologist Per-Olof Astrand once claimed?
Actually, no. Although athletic performance is influenced by genetics, scientific investigations have frequently found that it's even more dramatically shaped by training and motivation, not genes.
Looking at identical twins
Not surprisingly, many of these studies have focussed on what happens when twins embark on an exercise programme. The reason for using twins in the performance research is simple: if both twins and people plucked at random from the street begin a serious exercise programme, there will be a huge variation in response. Some individuals will improve their aerobic capacities by 50-60 per cent or more, others will achieve a more-usual gain of 20-30 per cent, and a few unfortunates will get an aerobic uptick of less than per cent.
However, if genes are important, identical twins should respond in a very similar fashion. If one member of a set of twins boosts maximal aerobic capacity (V02max) by 35 per cent, for example, the other should also raise aerobic power by about 35 per cent. If one twin lifts V02max by 10 per cent, his identical twin should also get about a I O-per cent gain. If performance is highly 'heritable,' eg, it can be passed on readily in genetic material, we would expect that identical twins would almost always respond to training in the same way.
On the other hand, if identical twins develop quite different performance capacities, it would be hard to argue that genes play a major role in determining the response to training. For example, if one twin gains 50 per cent and his identical twin increases aerobic capacity by only 10 per cent, we can figure that something other than genes is determining their performances. After all, their genes are identical, but their responses to training are quite different.
One person in 50 has a twin
Scientists interested in the genetics of performance are no slouches, so they usually include both 'monozygotic' and 'dizygotic' twins in their studies, as well as brothers and sisters. Somewhat surprisingly, it' s not hard to find twins for these studies. Although many people think that twinning is a fairly rare event, the truth is that about one out of every 100 births involves twins, which means that one person in 50 has a twin.
About 33 per cent of all twin pairs are identical (monozygotic), which means that they originated from exactly the same sperm-egg combination and have precisely the same genotype (their genetic constitutions are identical). On the other hand dizygotic (fraternal) twins, although born at the same time, come from different sperm-egg combos and are no more closely related genetically than 'normal' siblings. Dizygotic twins, brothers, and sisters share about 50 per cent of the same genes.
As a result, if genes really do determine performance, we wouldn't expect dizygotic twins and siblings to respond to training as identically as identical twins. However, fraternal twins and sibs should be more similar than people chosen at random from the overall population. To put it another way, monozygotic twins should have almost the same 10-K times, as long as their training is similar, dizygotic twins and siblings might have 10-K times a few minutes apart, and people chosen at random might have times ranging from 26:44 (the current world record) all the way up to 55-60 minutes. The less close the genetic relationship, the wider the variation.
Bear in mind, though, that we can't determine how much of any single person's performance is determined by genes, but we can assess how much of the VARIATION in performance within a group of people is attributable to genes. In other words, we can't tell Nick that, say, 40 per cent of his 10-K improvement from 47 to 38 minutes was the result of the DNA piloting his cells while the other 60 per cent resulted from his training, but we can estimate that 40 per cent of the variation in performance times in a population is due to genetic differences between members of the population. That's not very precise or individualised, but it does give us an indication of how important genes are in deciding what happens when people get serious about training. If 80 per cent of the variation was due to genetic factors, for example, we could sensibly conclude that the effects of genes far outweigh the effects of actual training.
The research results
So what have scientific studies actually found? Much of the best work has been carried out by Claude Bouchard, Ph.D., and his colleagues at Laval University in Quebec, Canada. In the early 1980s, Bouchard and co-workers decided to find out just how much variation in fitness could be present in a group of people who were training in a fairly similar manner. The goal was to eventually determine what portion of this variation was due to genetic factors and what portion was due to non-genetic influences such as nutrition, smoking habits, past exercise habits, age, socioeconomic status, etc.
In one of the first studies, 24 similar, initially sedentary subjects trained in exactly the same manner for 20 weeks. Although the training was identical, the people responded to training in disparate ways. Although the average gain in V02max was 33 per cent, one individual had gained 88 per cent, while another had increased aerobic capacity by only 5 per, cent - with exactly the same training programme!
Variation in actual performance, which was measured as the average power output a subject could sustain on a bicycle for 90 minutes, was also sizeable. Overall, performance soared by an average of 51 per cent after 20 weeks, and the biggest gainer was an individual who improved performance by 97 per cent, while the smallest improvement was made by a sad sack who advanced by just 16 per cent (less than 1 per cent per week).
These and later findings taught the Laval scientists that there are 'responders' and 'non-responders' within any population of people. The 'responders' make big improvements in aerobic power and performance as a result of their training, while the non-responders barely emerge from their sedentary physiological states, even after 20 weeks of vigorous work. Exercise scientists reckon that about 5 per cent of people in the population at large are high responders (they can improve by over 60 per cent), while about the same per centage are low responders (they improve by less than 5 per cent).
Are you a 'late bloomer'?
The Laval researchers also found that the time scale of training responsiveness varies a lot between people. Some are much better after just four to six weeks of training but may not improve after that, while others - the 'late bloomers' - are stagnant for six to 10 weeks and then really take off, improving their aerobic capacities by 20-25 per cent after 10 additional weeks of training.
How significant are genes in determining responsiveness and in deciding if you're a responder, a non-responder, a quick responder, or a late bloomer? To check that out, the Laval investigators placed 10 pairs of monozygotic (identical) twins on a 20-week training programme. The 20 subjects trained four to five times a week, 40-45 minutes per session, with average training intensity set at about 80 per cent of maximal heart rate. After 20 weeks, aerobic power burgeoned by 14 per cent, and 'ventilatory threshold' ;L - the exercise intensity at which breathing rate begins to increase fairly dramatically - improved by 17 per cent.
Identical twins respond identically
The most important finding, however, was that identical twins did in fact respond almost identically to the training programme. For example, one twin upgraded V02max by 10 per cent, while his identical twin improved by 11 per cent. Another gained 16 per cent while his twin settled for 14 per cent. Yet a third pair rested at 25 and 22 per cent. Overall, most of the variation in V02max was between, not within, sets of twins.
However, this does NOT mean that genetics are the most important factor which determines performance. All the twin studies demonstrate is that genes are important; they do influence the way people respond to training. They don' t tell us that genes are more important than training and other factors. We only know that genes do play some role and that identical twins will be more alike than dizygotic twins and siblings, who in turn will be more alike than non- ' related people. That's hardly earth-shaking news.
And, in fact the twin research offers some 'twists' which suggest that genes play a 'supporting' - but not 'lead' - role on the performance stage. For example, 82 per cent of the variation in V02max in the Laval twin study was due to genetic differences, but only 33 per cent of the difference in ventilatory threshold was attributable to genes. Somehow, genes were playing a strong role in setting aerobic capacity, but the environment (lifestyle factors and past differences in training) was considerably more important in fixing ventilatory threshold. That' s a key finding, since ventilatory threshold - and a closely related variable called lactate threshold - are often found to be the best predictors of actual endurance performance, better than aerobic capacity, anaerobic power, or efficiency of movement.
Married couples are equally similar
And there are other findings which put a dent in the idea that genes are paramount in shaping performance capability. For example, the Laval researchers found that spouses were as similar in their response to training as were brothers and sisters, even though the spouses were totally unrelated genetically. In other words, if Joe and Jean are married and begin training with Joe's brother John, Joe's gain in V02max is just as likely to be the same as Jean'.s as it is the same as John's! That' s hardly a ringing endorsement of the idea that genes play the crucial role in determining performance. In general, studies carried out with brothers and sisters suggest that genes explain only 20 per cent of the variation in observed performances. Training and lifestyle account for the other 80 per cent - or four times as much!
In addition, investigations which put mothers and their children on a training schedule have found that genetics explain just 28 per cent of the variation in V02max, even though a mum and her offspring share about 50 per cent of the same genes. That means that 72 per cent of the variation is due to training and other factors.
Sorry, dads, but the news is even worse for you. Investigations of fathers and their children have been unable to suggest that genetics plays any role at all in explaining variation in aerobic capacity, even though dad and son/daughter are 50-per cent alike! In other words, a father and his son are no more likely to respond to training in a similar manner than are two people selected at random on the street.
Why mother is best
Again, these findings hardly support the idea that great athletes are born, not made. But let's digress for a moment and consider why your mum is more important than your dad in determining how you'll turn out as an endurance athlete. The answer to this question rests inside tiny structures inside muscle cells called mitochondria, which provide most of the energy required for your endurance performances. The little mitochondria have their own genes, and all of the mitochondria in your body come from your mother, not from your dad, because your mum's egg contained mitochondria, while your father's penetrating sperm was mitochondria-free. As your foetal cells divided and formed muscle, nerve, and bone cells, they took with them mum's mitochondria. If she gave you good little mitochondria, you have a decent chance of becoming an endurance athlete; dad's mitochondria just don't count.
As you've guessed by now, genetics don't play the dominant role in producing top-level performances, but in addition to mother's mitochondria, there are some anatomical and physiological attributes which are highly heritable - and which can help you get to the finish line of a race more quickly. For example, your heart's 'coronary network' (the distribution and size of blood vessels within your heart) is genetically determined, as is the branching pattern of blood vessels which lead into your lungs. Total heart size is mildly heritable, and the volume of the heart's left ventricle - the key internal chamber which sends blood to your muscles - may be strongly determined by genes.
Muscle proteins, including key energy-producing enzymes, are also dictated by genes, as is muscle-fibre composition. If your mother and father had a high percentage of Type I muscle cells (the kind which have excellent aerobic potentials and promote superior endurance), your legs will probably also be biassed toward Type I cells, and you'll probably be a pretty decent marathoner. In fact, some studies have shown that muscle composition - or more specifically, the percentage of Type I fibres - can explain up to 90 per cent of the variation in race times observed during the 26.2-mile race. Metabolism of fat is also at least partially genetically determined.
However, the bottom line is that your genetic endowment is really just the stage upon which your training, nutrition, and motivation act out their important roles and produce your ultimate performances. Even mum's mitochondria and the genes which control heart size, muscle composition, and fat metabolism are only up to explaining about 30 per cent of the variation in performances in Great Britain, the United States, Timbuktu, and any where else. The rest of the variation - about 70 per cent - is due to the environment, e.g., training and lifestyle factors.
So, the next time you line up at the start of a race, remember that genes have indeed played a role in determining how long it will take you to get to the finish line but that your training and nutritional practices have had an even larger impact! That's good news, because it means that your destiny as an endurance athlete is to a great extent under your own control.
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