Top marathon runners tend to be lean and light, star swimmers are gangly things with huge feet and gold medal weightlifters are solid blocks of muscle with short arms and legs. So does your physique - and indeed the way your body works - fit you for a particular sport, or does your body develop a certain way because of your chosen sport?

"It's about 55:45, genes to environment," says Mike Rennie, professor of clinical physiology at the University of Nottingham Medical School in Derby who cites the case of identical twins from Germany, one of whom was an endurance athlete, the other a power sportsman, "They look quite different, despite being identical twins."

A five footer has little chance of becoming an elite basketball player, but being six foot nine with the springiest tendons in the land doesn't automatically propel you to Olympic gold.

Craig Sharp, professor of sports science at Brunel University, made this point at a recent Royal Institution event at which the limits of human performance were debated. "Unless you have tactical sense where needed, unless you have access to good equipment, medical backup and the psychological conditions to have the winning attitude and be able to drive yourself through pain, and of course, superb technique, all the physical side will be in vain."

Jonathan Robinson, an applied sports scientist at the University of Bath's sports development department, underlines the importance of technique. "In swimming, only 5-10% of the propulsive force comes from the legs, so technique is vital." To illustrate his point, he cites triathletes, who are all extraordinarily fit, yet who may fail to reach competition standard if their swimming technique is poor.

But having the right physique for the right sport is a good starting point. Seventeen years ago, the Australian Institute of Sport started a national Talent Search Programme, which scoured schools for 14-16-year-olds with the potential to be elite athletes. One of their first finds was Megan Still. In 1987, she had never picked up an oar in her life. But she had almost the perfect physique for a rower. After intensive training, she won gold in women's rowing in the 1996 Atlanta Olympics.

Other countries have followed the Australian example. The explosion of genetic knowledge has meant that there is now a search, not just for sport appropriate physique but also for "performance genes". Several are implicated. For instance, the ability to use oxygen efficiently is key to gaining the winning edge. The EPOR gene initiates the process of red blood cell production and then switches off, but one mutation means that it carries on working, leading to an abnormal amount of red blood cells. Finnish researchers identified an entire family with this EPOR mutation, several of whom were championship endurance athletes, including the great cross-country gold medalist skier, Eero Mantyranta. This mutation was definitely performance-enhancing. Craig Sharp believes that elite athletes of the future may well come from among such physiological "outliers", people who naturally possess extremes of normal physiology which also happen to be performance-enhancing. "It's a question of finding them," he said at the RI.

The drive to pick elite athletes based in part on body shape or characteristics has had a difficult history, with work bedevilled by the race issue. Competitors of African origin hold most of the leading times for top running events, even though only one in eight of the world population is black. And Kenyans from the Kalenjin tribe hold 40% of the top honours for distance running.

These Kenyan runners tend to have slim legs, with high calf muscles (a genetic trait), which is a very efficient anatomy for a runner. But, they also live above 2,000ft, which helps to increase the body's amount of red blood cells as well as its cardiovascular capacity, which are both vital for long distance running. And since runners are national heroes, and running requires no more equipment than a pair of shoes, there are considerable rewards for training intensively.

In truth, there is more genetic variation between individuals than there is between races. All we may be seeing is encouragement for those of a similar skin colour to train hard and be the best.

But, so far, what do we know about the different physiological types suited to particular sports?

Rowing

The perfect male rower is an extraordinary physiological specimen. He is tall, heavy but with very low body fat (10% in men), with broad shoulders and long, powerful limbs. His heart is capable of pumping 40 litres of blood a minute. Rowers have the highest absolute maximum oxygen uptakes of any athletes and the highest intakes of air, up to 300 litres per minute.

Shooting

You might think a sport that requires you to lie down, doesn't require fitness. But perfect shots have very good cardiovascular fitness and a low heart rate, which they can slow further. Within seconds of firing, they can (without knowing it) drop their heart rate by 20 beats and fire exactly between heatbeats. Pistol shooting also needs strong upper body musculature.

Swimming

The perfect swimmer is tall, with very long limbs, particularly arms. Top-class swimmers have big feet, which provide a huge propulsive advantage. They have big hands to act as paddles, narrow hips to reduce drag and broad shoulders to maximise arm power. Sprint swimmers are more mesomorphic, with high power energy systems.

Sprinting

dThe perfect 100m sprinter is tall, with a strong mesomorphic body shape. Top sprinters have slim lower legs and relatively narrow hips which gives a biomechanical advantage. They have a high percentage of fast twitch fibres (more than 80%). They use muscle fuel so fast that they are practically running on empty by the end of the race.

Marathon running

The perfect marathon runner has a light frame, slim legs and is of small to medium height. They have high percentage of slow twitch fibres and very high maximal oxygen uptake. They can withstand dehydration, and training gives their muscles a high storage capacity for the premium muscle fuel, glycogen.

Gymnasts

The perfect female gymnast is small and slim, with a high strength to weight ratio and an even musculature. Unusually, she will have grown steadily, rather than in spurts, during her early adolescence. She has a narrow body to permit speedy rotation and superb balance. Gymnasts of both sexes require both high power and high capacity energy systems and, overall, are the fittest of all athletes.

Weightlifting

The perfect weightlifter has a strongly mesomorphic body type, and is very well muscled. Good weightlifters are not tall and tend to have relatively short arms and legs, which makes them more effective levers. They have cardiovascular systems able to stand sudden surges in blood pressure). High percentage of fast twitch fibres.

Morphs and muscles

Body type: ectomorph, mesomorph, endomorph?

Mesomorphs have well-defined muscles and large bones, with a low, narrow waist. Men are rectangular, and women are hourglass-shaped. Ectomorphs are skinny, lightly muscled with thin wrists and ankles. Endomorphs are round and soft, with relatively short limbs, high waists, small hands and feet. Most people are mixtures of body types, but those who are strongly mesomorphic tend to do well in sports such as weightlifting, while running is where ectomorphs are found to excel.

Body physiology: high power or high capacity?

To determine your physiological type, it is useful to think of your muscles as being powered by batteries (in reality, they are fired by three different types of cellular fuel). Some people's muscles have a much greater capacity to deliver big bursts of power for short periods, while others are better at delivering a smaller amount of energy over a sustained period. The former group are suited to power events and the latter are better adapted to endurance sports.

Muscle composition: fast twitch/slow twitch?

Muscles are made up of two different types of fibre. The "fast twitch" fibres deliver extreme amounts of power for a few seconds, whereas "slow twitch" fibres deliver prolonged contraction over many minutes or hours. The ratio of fast to slow fibres in each person is inherited. Those with more slow twitch fibres favour endurance events. Individuals with fast twitch fibres favour sprint events or those requiring sudden power, such as weightlifting.