Asafa PowellAsafa Powell

The banned drug oxilofrine that top Jamaican sprinters Asafa Powell and Sherone Simpson have tested positive for is a stimulant used to boost the body’s ability to burn fat.

The substance helps athletes boost their power-to-weight ratio with more lean muscle and less fat, and so increase their speed.

It may also increase the rate at which the heart reaches its maximum performance during exercise, meaning a greater supply of oxygen can get to the muscles earlier.

Oxilofrine is an agent that stimulates part of the nervous system and was previously used to treat low blood pressure.

More recently, it has started to appear in combination with caffeine in dietary supplements marketed as weight loss products.

However, the superiority of using oxilofrine over an exercise warm-up to achieve this appears unconvincing.

Simpson, 28, who finished equal second in the 100 metres at the 2008 Beijing Games and won a gold medal in the 2004 Athens 4x100 metres relay, denied knowingly taking the banned substance.

“This is a very difficult time for me,” she said in a statement.

“As an athlete, I know I am responsible for whatever that goes into my body. I would not intentionally take an illegal substance of any form into my system.”

There have been no previous findings in Britain but competitors in cycling, athletics, weightlifting, rugby union and American football have been banned in the last three years.

They include American Amy Dodson, one of the world’s top amputee runners, who received a six-month ban in 2011 and US cyclist Flavia Oliveira who was suspended for 18 months in 2009.

Both said they had unknowingly ingested the stimulant via an over-the-counter supplement.

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