Which supplements do athletes take and why?

It was at the 1992 Olympics in Barcelona when the mutterings about a new "secret weapon" started.

Dozens of Great Britain athletes had been taking a new product that increased muscle mass and improved athletic performance – a "wonder pill" that didn't fall foul of any doping rules.

Now found in tubs and bags on many supermarket shelves and tagged in your social feeds, it is the supplement of choice for millions of people and one of the most scientifically researched.

But back then, when it came on the scene at the very top of British elite sport, there were suspicions and stigma around the use of any substance described as 'performance enhancing' – even if it was legal.

From the minute an athlete wakes, to the moment they go to bed, they are thinking about how they can optimise their performance and recovery.

Today, creatine is just one of a long list of supplements taken by elite athletes in this pursuit of marginal gains. Some help with muscle size and strength, while others correct deficiencies in the diet.

"There are various reports in the literature of some studies that say maybe up to 90% of athletes take supplements. I often jokingly say that means 10% are lying," says Prof Graeme Close, professor of human physiology at Liverpool John Moores University.

"The sports teams that I've worked in, I think that's probably closer to 100% of athletes will be taking some form of supplementation."

So, what do supplements actually do and why do athletes take them? And in the world of strict liability, where elite athletes are solely responsible for what they put in their bodies, how do they make sure they stay clean?

While experts like Close advocate for seeking to meet nutritional needs through food in the first instance, it may not always be possible or practical to do this - and that is where supplements come in.

Take, for example, creatine, which is found naturally in meat and fish.

"You would need the best part of a kilogram of raw chicken a day to get the amount of creatine you need," says Close. But it is unsafe to eat raw poultry because of the food poisoning risk from harmful bacteria.

Creatine is a natural compound in the body produced in the kidneys, liver and pancreas. It is a quick source of energy for muscles, which is especially important for short-duration, high intensity activities such as sprinting.

Its big break as a supplement came in the 1990s when two scientists who had been researching it for two decades shared their findings with Steve Jennings, whose Maxim sports nutrition company supplied products to the British Olympic team.