They’re supposed to be about making parasports fair, but the category system central to disabled sports and the Paralympics, which classifies athletes according to their impairment, is increasingly under fire.

French swimmer Theo Curin, whose lower legs and hands were amputated after a bout of meningitis as a child, is sitting out the Tokyo Games over his unhappiness with the system and how athletes are assessed.

“Overnight, two people who swim with both their hands appeared in my S5 category. You don’t have to be very smart to understand that having two hands in swimming helps a lot,” the 21-year-old said.

“There are a lot of flagrant inequalities that annoy me and are really ridiculous,” he said.

Ten types of impairment are accepted at the Paralympics, broadly covering physical, visual, and intellectual disabilities. But within each impairment category there are a vast range of abilities, so athletes are further divided by class in a system designed to ensure people compete against others with approximately the same capabilities.

In swimming, for example, each class has a prefix – S for freestyle, butterfly and backstroke, SB for breaststroke, and SM for individual medley – followed by a number.

Physical impairments cover numbers 1-10, with the number lower the more severe the impairment. Vision impairments go from 11-13, while 14 indicates intellectual impairment.

The system is complicated and time-consuming, and some athletes feel it is failing.

Curin was supposed to be in the pool at Tokyo’s Aquatic Centre this year, as one of France’s top para-athletes, with nearly 150,000 Instagram followers. He made his Paralympic debut in Rio, aged 16, and just missed out on a spot on the podium.

But instead of chasing a medal in Japan, he’s making a film and preparing to swim across South America’s Lake Titicaca.

“I decided to put aside Paralympic swimming so long as these problems with classification continue,” he told AFP. “They’ve left me a bit disgusted with the Paralympic movement,” the three-time World Championship medalist said.

‘Incentive to cheat’

Curin is not the only one who feels the system is flawed, with particularly fierce debate surrounding classification in the pool.

US swimming star Jessica Long, who won her 14th Paralympic gold on Saturday, has said “the incentive to cheat is huge” given the increasing fame and financial rewards enjoyed by successful para-athletes.

“I can’t watch this sport that I love continue to get destroyed like this,” she told Sports Illustrated last year.

The International Paralympic Committee defends the system, asserting that “sporting excellence determines which athlete or team is ultimately victorious”.

“Disappointingly, what we have witnessed in recent years is a small number of athletes... struggling to come to terms with increased competition,” it said.

“Rather than embrace the improved competitive nature of their Para sport, they have instead questioned the classification of their competitors, despite the fact that international classifiers have found their rivals to be in the correct class.”

But critics of the system point to what they say is the arbitrary and unscientific nature of the assessments involved.

The exams are “done by eye and based on the feeling of the observers”, French swimmer Claire Supiot told FranceInfo. She was reclassified earlier this year from S8 to S9, making “the road to the podium significantly harder”.

There are also allegations of athletes trying to game the system, trying to be placed in a more severely impaired class to gain an advantage.

In 2017, a former classifier told the Guardian newspaper on condition of anonymity about athletes taking hot or cold showers, rolling in the snow or bandaging their limbs to appear to have more limited ability during exams.

Curin went through two rounds of exams, the first of which – a medical examination – produced a provisional classification at the lower end of S4.

But after a second round in which he was observed in the water, he was given a final class of S5.

That, he said, penalises him unfairly, “because I know how to properly work with my disability”.