2016 Rio Olympic Games in Brazil Aug 05-21,2016 - Olympic swimmers at the very peak of their fitness as they compete for once-in-a-lifetime glory

Burning hundreds of calories and working virtually every muscle in the body, swimming is one of the most physically-demanding disciplines at Rio 2016.

It was one of the original nine sports at the very first modern Games in 1896  and athletes now compete across four strokes - freestyle, breaststroke, butterfly and backstroke.

As water is 12 times denser than air, the sport requires physical strength as well as stamina, meaning athletes must be at the very peak of their fitness to compete in the Olympics.

Synchronised swimmers must also be able to hold their breath for between two and three minutes, and are not allowed to touch the bottom of the pool during their routine. 

Swimming makes intensive use of the body's energy supplies, with a normal-sized person moving at a fast pace burning around 800 calories an hour.

Team USA's Michael Phelps claims to consume 12,000 calories a day, the equivalent of eight whole chickens.

The 18 times gold medal-winner starts the day with a hearty breakfast consisting of three fried-egg sandwiches, three chocolate chip pancakes and a five-egg omelette. 

And that is in addition to three sugar-coated slices of French toast and a bowl of maize porridge