A young British woman developed a potentially fatal blood clot from exercising too much, doctors said.

Danielle Yallop, 24, had to have emergency surgery to remove a rib after being struck down by a deep vein thrombosis that was caused by her fitness regime, Manchester Evening News reported Thursday.

Yallop, who worked out at the gym five times a week, had noticed a lump under her arm shortly after traveling on a long-haul flight to the U.S.

She was given blood clot-busting drugs and surgeons had to remove her rib to ease the pressure on her arteries.

Professor Mo Baguneid, a specialist at The Alexandra Hospital, near Stockport, northern England, where Yallop was treated, said it was impossible to say how much exercise is safe.

"A lot of the time it's caused by upper arm exercise -- some people are more prone to it but it can affect anyone," he said. "We call it Effort Thrombosis because it's due to exercise. The only advice I could give people is to build up gently and not to over-do it in the gym."

He added, "It's becoming more of a common problem. I've treated three in the past two months -- they were all young people under the age of 30 -- not the type of patient you would expect for this condition."

Yallop, who works in soccer giant Manchester United's marketing department, said, "It won't stop me from exercising, that's a big part of my life, but I think I'll probably take it a bit easier because it was pretty scary to get a blood clot."

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