We know that one of the things that distinguishes elite athletes is their tolerance of pain. Ask Manteo Mitchell, the US runner who refused to slow down despite feeling his leg break halfway through an Olympic relay race this month. No pain, no gain, right? But what if gain required hammering a nail into your foot, or electrocuting your testicles?
The extreme lengths some athletes go to to win have emerged days before the start of the Paralympic Games. According to a scientist who works with disabled competitors, as many as a third of those with spinal injuries may be hurting themselves in an attempt to reach a level playing field with their rivals.
Brad Zdanivsky, a 36-year-old Canadian quadriplegic climber, told the BBC World Service that he had experimented by at first ignoring the will to urinate and, later, by "using an electrical stimulus on my leg, my toe and even my testicles".
Tanni Grey-Thompson, the veteran British wheelchair racer, says she had heard of an athlete who tapped nails into his feet. One other reported method involves breaking toes with hammers.
The technique is known as boosting and, crucially for athletes who do it, it doesn't actually hurt, although it can be uncomfortable and potentially dangerous. The aim is to increase blood pressure, which aids circulation and gives a short-term boost in performance during training or competition.
Able-bodied athletes, or Paralympians with a naturally higher blood pressure, automatically achieve the effect after they start to exert themselves, but many athletes with paralysis are at a disadvantage unless they can find an alternative method. A self-inflicted injury can induce an effect called autonomic dysreflexia, which can provide the solution.
Boosting is banned by the International Paralympic Committee (IPC), but it can be hard to detect and there are no reliable statistics on the number of athletes who do it. Around 17 per cent of 60 Paralympians surveyed in Beijing in 2008 admitted to boosting, but Dr Andrei Krassioukov, an associate professor at the University of British Columbia in Canada and a spinal injuries expert, said the figure could be closer to 30 per cent.
A spokesman for the British Paralympic Association told us yesterday: "Autonomic dysreflexia (AD) occurs in a proportion of athletes with high spinal cord injury. The intentional induction of AD is termed "boosting" and it is considered to be dangerous to the health of an athlete to compete in a dysreflexic state. Athletes who are susceptible to this condition may be tested by the IPC prior to competition to ensure they are not in a dysreflexic state."
The body, which is sending almost 300 athletes to the Games, added: "ParalympicsGB has included education about this for all our athletes and we do not perceive this to be an issue with any British athletes."
Zdanivsky, whose spine was crushed in a car accident in 1994, admitted boosting could be risky. "You are getting a blood pressure spike that could quite easily blow a vessel behind your eye or cause a stroke in your brain," he said. "It can actually stop your heart. It's very unpleasant, but the results are hard to deny... so it doesn't matter if it's unpleasant; it gets results."