He was diagnosed with ADHD at age 9 for which he required daily doses of the drug Ritalin. But this did not stop him from pursuing his goals for swimming.
The most decorated Olympian of all time is not only one of the tallest swimmers in the pool at 6 feet 4 inches but also has an even bigger arm span at 6 feet 7 inches. His disproportionately long torso allows him to generate force from his body's core, allowing him to shunt great volumes of water behind him.
Phelps also has the legs of a man who's only 5 feet 10 inches, which provides him with more efficient kicking. This in turn helps him save energy by using fewer strokes than his other swimming counterparts.
He has a specially built Speedo suit that is woven specifically to reduce drag. His size 15 feet are so flexible he can lie flat on his back, arch his feet and curl his toes to touch the ground.
His unique physiological build also attests to his amazing stamina as he produces far less lactic acid than other athletes under aerobic strain, so he recovers faster.
After he set the 100-meter butterfly world record in 2003, Phelps' blood lactose level was an absurdly low 5.6 millimoles/litres of blood, half or a third that of other top swimmers. He can also tolerate high levels of blood lactose and swim at full pace on levels that is not possible for other athletes.
As he competed in heats and finals in Beijing, researchers say he swam enough laps to equal a runner having to finish eight 26-mile marathons.
