THIS SUMMER, top athletes from around the world will converge on London to try (among other things) to run, swim, cycle and walk faster than ever recorded. To jump longer and higher, to throw further and to lift heavier weights.

The Olympics offers a gripping four-yearly showcase of human athletic performance. But what is it about elite athletes that allows them to compete at that extreme level? And why will most of us sitting on the couch watching them never make it to the winners’ podium?

The making of an elite athlete can include genetics, a bit of luck and the unavoidable slog of training for many years, and science is helping where it can.

For some sports, such as running at elite level, genetics can play a role, particularly when you compete at the extremes of the more “explosive” events, such as the 100m sprint, and endurance events, such as the marathon.

“There are two types of muscle fibre: fast twitch and slow twitch, and to be a good sprinter, primarily you need a lot of so-called fast-twitch muscle fibres in your leg muscles,” explains Colin Boreham, professor of sports science at University College Dublin. He competed as a decathlete for the British team alongside Daley Thompson in the 1984 Olympics in Los Angeles.

“Fast-twitch muscle fibres not only contract twice as fast as the slow-twitch fibres when you require them to do so, but also they don’t rely on oxygen for their energy, so they tend to tire rather quickly,” he adds.

The leg muscles of elite endurance runners would be richer in slow-twitch fibres, he says. “Slow-twitch fibres have the machinery to produce their energy aerobically – they have more capillaries surrounding them to deliver blood and oxygen, they have more mitochondria [energy-producing structures in cells] and more myoglobin, which transmits the oxygen to the mitochondria. All of this makes them more aerobic – so while they don’t contract as quickly as fast-twitch fibres, they do contract for longer before they fatigue.”

Whether you are a fast or slow twitcher is mainly genetic. “You are born with it by and large,” says Prof Boreham. “If you do a lot of training you can gradually change the fast fibres to the slow type. This may take several years of chronic training six or seven days a week, hours each day.

But you can’t do it the other way around, you can’t change slow to fast – so for sprinters or middle distance runners who do a lot of training, as the years go by they tend to go up a distance. And probably one of the reasons is that the muscle-type profile in their legs is changing slightly.”

However, Boreham, who directs the Institute for Sport and Health at UCD, also notes that there is no single gene that determines speed, endurance or flexibility, and several other factors also come into play in selecting a champion.

“You need the right environment to spot talent and develop it,” he says. “You could have the right genes to be a fabulous rower an indoor track cyclist or fabulous swimmer, but if you don’t live in the right country with the right economic circumstances, you are not going to make it.”

And even if everything else lines up, there’s no way around the need to train if you want to compete at that level.

Dr Giles Warrington, a lecturer in sport at Dublin City University’s School of Health and Human Performance, offers the example of swimmer Michael Phelps, who has won 16 Olympic medals.

“Phelps is perfectly shaped for [swimming],” he says, describing how his height, “wing span”, relatively long torso and short legs, size 14 feet and hyperflexible elbows and ankles suit the task. “But does he still need to train? Yes, for six or more hours a day.”

It typically takes athletes many years of training and deliberate practice to get to the level where they can consistently compete successfully at international level, he adds.

“If you take the example of Sonia O’Sullivan, her training age would have been about eight to 10 years when she was at peak condition, when she was competing at the very highest level.”

And training is becoming more scientific and evidence-based, according to Warrington, who is head sports physiologist and sports science adviser to the Olympic Council of Ireland.

He explains that advances in sensor technologies mean researchers and coaches can gather data as athletes train without impinging on performance. Then the data can help inform and tailor the ongoing training programme. “For a lot of sporting events, the difference between success and failure is marginal, you might be talking hundredths of a second, which is statistically non-significant, but there is a performance difference.

“If you were purely looking at it as a study you might discount it, but if you were giving an athlete half a metre they might take that.”

Dr Ian Kenny, a lecturer in sports biomechanics at the University of Limerick, also highlights how more “user-friendly” monitoring technology can help in field-based assessments when his group works with athletes such as rugby players. Athletes are brought into the lab to analyse how their muscles react to fatigue, and field-based monitoring is carried out as players train.

“We are able to assess or track someone’s movements in the lab or field without wires attached, so they are not in an environment which makes them think they are being imposed upon or tested overly,” says Kenny.

“We can use GPS technology to track types of movements, whether it’s walking or running, and the intensity and endurance of athletes when they are on the pitch. That will help inform the coaches whether to rest them or to work them harder from week to week. It allows you to build up a structured programme that will help them better achieve their potential.”

Usain Bolt: The perfect athlete?

Usain Bolt (lpictured) was, it seems, born to run. And he has crashed through world records over short distances: here is someone who can run 100m in 9.58 seconds.

Part of his ability is down to the composition of his leg muscles. We are born with a certain make-up of muscle fibres in our legs, which include “fast-twitch” fibres, which can contract rapidly but tire easily, and “slow-twitch” fibres, which contract more slowly but can go for longer. Fast-twitch muscles are the ticket for sprinting.

“The average man and woman have about 50 per cent fast and 50 per cent slow fibres in the big thigh muscles,” explains former Olympian decathlete Prof Colin Boreham. An Olympic sprinter such as Usain Bolt would certainly have 80 to 90 per cent, and maybe even 95 per cent fast muscle.”

But Bolt is unusual in that he is an extremely tall sprinter, at around six feet five inches. “Sprinters tend to be on the shorter side, under six feet,” says Boreham. “Having shorter [legs] gives them an advantage at the start, they can get their legs moving quickly over that critical first 30 to 40m. But even though Bolt is taller, he is so powerful he can get his legs running as fast as competitors.”

Had Bolt not trained as an elite athlete, he would likely still be able to run short distances faster than most people.

“He is supremely talented, he would still be very fast with no training at all,” says Prof Boreham. “He would probably be able to run 100 metres in, I would guess, around about 10.6 or 10.7 seconds.”

But years of training have sped up Bolt’s sprint times over that distance by about 10 per cent, says Boreham. “He is the perfect athlete.”