Would you break your own toe to win a Paralympic medal? Would you sit on a sharp object or strangulate your testicles? It's cheating, but a scientist who will be monitoring athletes at the Paralympic Games says a third of competitors with spinal injuries may be harming themselves to boost their performance.

The practice, called "boosting", is designed to increase blood pressure and enhance performance.

It's banned by the International Paralympics Committee (IPC), but some researchers say these are the desperate acts of athletes trying to compete on a level playing field.

"There have been times where I would specifically give my leg or my toe a couple of really good electric shocks" says Brad Zdanivsky, a 36-year-old Canadian quadriplegic climber who has experimented with boosting in the gym.

Common boosting techniques Overfilling the bladder, by clamping a catheter

Sitting on a drawing pin

Use of tight leg straps

Twisting and/or sitting on the scrotum

Cracking or breaking a bone

"That would make my blood pressure jump up and I could do more weights and cycle harder - it is effective."

One British journalist with years of experience covering the Paralympics says he has heard of athletes using small hammers to crack or break a toe.

The point of these activities is to raise the athlete's blood pressure and heart rate.

Isn't high blood pressure bad? High blood pressure causes millions of deaths each year around the world, so it may come as a surprise to hear of athletes deliberately "boosting" theirs. But a raised heart rate and blood pressure are advantages during exercise, as they help deliver more oxygen to hard-working muscles, enabling the athlete to keep going. For most people, heart rate and blood pressure rise naturally when physical activity increases. But this is not always the case after a spinal cord injury, meaning competitors could tire sooner. In the world of elite sports, "boosting" could make the difference between winning and losing. But it also boosts the chance of a heart attack or stroke.

When able-bodied competitors engage in hard physical activities like running or swimming, blood pressure and heart rate increase automatically. Athletes with spinal injuries do not get that response. "Boosting" is a short cut to higher blood pressure and the improved performance that comes with it.

In medical terms it's defined as the deliberate induction of a dangerous condition common to quadriplegics called autonomic dysreflexia (AD). Many everyday activities that cause discomfort, even something as trivial as sunburn, can set off the condition naturally.

Zdanivsky turned to boosting when his spine was crushed in a car accident in 1994, because he didn't want the injury to curb his passion for mountain climbing.

"I tried several different ways of doing it. You can allow your bladder to fill, basically don't go to the bathroom for a few hours and let that pain from your bladder do it.

"Some people do that in sports by clipping off a catheter to let the bladder fill - that's the easiest and the most common - and you can quickly get rid of that pain stimulus by letting the urine drain out.

"I took it a notch further by using an electrical stimulus on my leg, my toe and even my testicles."

But boosting comes at a price.

"You are getting a blood pressure spike that could quite easily blow a vessel behind your eye or cause a stroke in your brain," says Zdanivsky.

Image caption Brad Zdanivsky is a passionate mountain climber

"It can actually stop your heart. It's very unpleasant, but the results are hard to deny. The saying is that winners always want the ball, so it doesn't matter if it's unpleasant, it gets results."

The IPC has been aware of the problem for many years. Boosting has has been banned since 1994.

But remarkably little scientific research has been done to assess how many athletes are willing to take these extreme measures to improve their performance.

A survey carried out by the IPC during the Beijing Paralympics indicated that around 17% of those who responded had used boosting. Some experts believe the real figure could be higher.

Could it be as high as 30%, I asked Dr Andrei Krassioukov, a professor of medicine at the University of British Columbia and an experienced researcher into spinal injuries?

"Correct. It is possible," he replied.

"I will tell you right now as a physician people want to feel better, first of all - they feel better with their blood pressure higher. But a second thing driving it is the desire to win, to have a fair playing field with other Paralympic athletes who have higher blood pressure."

While many athletes with spinal injuries will suffer from low blood pressure, there is considerable variation from one individual to the next.

Athletes' confessions in Beijing survey Participants were specifically asked the question: "Have you ever intentionally induced autonomic dysreflexia to boost your performance in training or competition?" Of the 60 participants who responded, 10 (16.7%) responded affirmatively while 50 (83.3%) responded negatively. All the positive responses were obtained from the male participants, with the majority competing in wheelchair rugby (55.5%), followed by wheelchair marathon (22.2%) and long distance racing (22.2%) Beijing survey for World Anti-Doping Agency

"There is still a disadvantage between paralympians who have normal blood pressure and those who don't and this puts a significant number of athletes at a disadvantage," Krassioukov says.

"As a physician I totally understand why these Olympians are doing this, but as a scientist I am horrified with these events."

He believes that changes to the system of classification would help - for example by changing the points system that aims to ensure that teams with a roughly equal level of overall disability compete against one another in wheelchair rugby and basketball.

Currently, the system takes no account of blood pressure and heart rate.

IPC Chief Medical Officer Peter Van de Vliet says he has no data that would support or disprove Krassioukov's estimate that up to 30% of paralympians with spinal injuries engage in boosting.

It's an unacceptable practice, he says, and the IPC has no sympathy with the idea that it levels the field of play.

Image caption Some wheelchair rugby players said they had tried boosting

The IPC has no plans to add physiological characteristics into their classification systems, he adds.

"Paralympic qualification for athletes with physical impairment is on the basis of a neuro-muscular-skeletal impairment rather than a physiological one," he says.

IPC rules on boosting The IPC forbids athletes to compete in a hazardous dysreflexic state

A hazardous dysreflexic state is considered to be present when the systolic blood pressure is 180mm Hg or above

An examination may be undertaken by physicians or paramedical staff... at any time

Any deliberate attempt to induce Autonomic Dysreflexia is forbidden... the athlete will be disqualified from the particular competition IPC position statement

During the Beijing Games, the IPC carried out about 20 blood pressure checks on athletes before events. They didn't find any clear evidence of people boosting.

The IPC says it will continue to monitor athletes closely before events at the London Games.

Anyone they suspect is boosting - symptoms include sweating, skin blotchiness and goose bumps - will be subjected to blood pressure checks.

If athletes are found to have a systolic blood pressure of 180mm of mercury or above, they will not be allowed to compete in "the particular competition in question". But they will not receive a long-term ban.

Brad Zdanivsky argues that checks like this will not be effective in cutting out boosting. He says you would need to test an athlete's blood pressure regularly over a sustained period to be able to know for sure whether any given reading was natural or "boosted".

"There is no real solution, it is an ugly can of worms that no-one wants to open it and talk about," says Zdanivsky.

He believes that only a tragic event will bring the problem out into the open.

"What's going to happen one day is that someone is going to have a stroke right on the court and then they are going to have to talk about it."

Matt McGrath's documentary Cheating at the Paralympics will be broadcast at 1832GMT on 23 August 2012 on the BBC World Service