One has acquired more Olympic medals than any other athlete in history; the other was knocked out of the Games after just 250 seconds. But Michael Phelps and Ashley McKenzie, the 23-year-old British number one judoka, have one thing in common: both have attention deficit hyperactivity disorder (ADHD), as does another high-profile Olympian, British gymnast Louis Smith, who this week helped to win the first British men's gymnastics team medal for a century.
Suddenly, a condition that is hugely stigmatised and still controversial is unexpectedly in the spotlight. It raises several interesting questions. Does ADHD hinder or help sporting success? And can the Olympics offer a positive legacy for people suffering from it?
Phelps, the American swimmer with a record-breaking 19 Olympic medals to his name, is probably the most famous person in the world with ADHD.
For Phelps, a gangly, hyperactive child who was diagnosed with the condition aged nine, the swimming pool was a sanctuary, a place to burn off excess energy. His mother, Debbie, recalled a teacher once telling her: "Your son will never be able to focus on anything."
But the boy who was unable to concentrate at school would sit for four hours at swimming events waiting to compete in five minutes of races.
Smith has spoken of how gymnastics was an outlet for his tremendous energy and taught him discipline and manners. But McKenzie's story is perhaps most dramatic of all. Expelled from three schools and placed in a psychiatric unit at age 11 because his mother was unable to cope, McKenzie also served time in a young offenders' institute.
He credits judo with saving him from prison and in a recent BBC documentary called it a "mad booster" to his life, giving him "a pavement instead of walking on the road".
"I don't want to be looked at as 'he's got ADHD and he's the bad person'. I've changed now," he said.
But it is not as simple as sport rescuing him. McKenzie served three bans from judo for drinking and fighting, and on the last night of the Team Great Britain training camp he went out to celebrate his 23rd birthday and told a stranger at a bar: "I'm gonna smash your face in."
The disorder may give him energy, but his sporting career is actually a hindrance to tackling his condition: he cannot take the medication he needs to treat his ADHD because it contains substances banned by the sporting authorities – hence his struggle to control his behaviour.
More athletes will almost certainly be undiagnosed or keep it quiet, such as Adam Kreek, a Canadian rower who won gold in Beijing. Two years later, he began talking openly about his condition.
"I found that the disorder isn't a negative affliction, but it gives positive energy as well," Kreek, who is now a motivational speaker, said in 2010.
Diagnosed at the age of six, he believes anyone with the disorder can train their mind to channel their "incredible" energy. As well as a good diet and family support, he found "rowing to be an outlet to control my ADHD".
It can be a confusing condition because people may be fidgety and unable to focus and yet – as Phelps so spectacularly proved – are capable of concentrating intently on an activity they find rewarding.
Children with the disorder, says Andrea Bilbow, founder and chief executive of a British charity organisation Attention Deficit Disorder Information and Support Service, are often brilliant at computer games. Psychiatrists say that this "hyper-focusing" is a relatively common feature in individuals with ADHD.
Athletes like Phelps and McKenzie do not, however, get special powers from their condition. Bilbow believes it is actually significantly harder for people with the disorder to become elite athletes.
"Having ADHD doesn't mean you're going to be a great sportsperson," Bilbow says. "Your ADHD isn't going to get you there; it's hard work that will. ADHD is not a contributor towards success, but equally it is not a barrier to success."
People with the developmental disorder might find they have poor problem-solving skills and struggle with keeping time, organising and motivating themselves, says Bilbow. This may suggest that adapting to the discipline that athletic training demands is tough for those with ADHD. Yet Bilbow believes many with the condition find that sport gives them the kind of immediate rewards and sense of achievement they need to build confidence and resilience.
After his early exit in the judo, McKenzie has vowed to come back stronger in Rio in 2016. Bilbow hopes he can get the extra help he will need in the coming years. She works with parents whose children have ADHD and believes more of them could find sport a constructive way of managing the condition, rather than being preoccupied with academic success.
Her two sons, Max and Joe, both have ADHD. Max, who is 29, finds an outlet for his energy in elite kayaking and Joe, who is 25, is an Olympic volunteer. Her advice to parents? "Find your child's island of competence and invest in it heavily."
Bilbow has noticed that children with ADHD may have their sporting opportunities curtailed as punishment for their behaviour, as McKenzie found. She knows of a brilliant young footballer who was barred from representing his school because of his conduct in lessons.
Many teachers and schools, she says, still scoff at the disorder, believing there are only naughty children – and bad parents.
The concept of role models can seem an overused cliché, but the Olympians with ADHD may really inspire a generation of athletes who once would have been written off.
"Parents can be saying to kids who are having a miserable time in school: 'Look, Michael Phelps had ADHD and he worked really hard. Ashley McKenzie has been in a young offenders' institute but he didn't give up,'" says Bilbow. "That's the message we've got to give children." – © Guardian News & Media 2012