It is the excitement of this unpredictable and dangerous challenge that motivates the predominantly young male participants

Research team

But some suffered potentially fatal injuries, including spinal cord damage, air and blood trapped in the lungs and the loss of a kidney.

Doctor Lee Jeys, who led the study, said mountain bikers should use protective equipment to guard against serious injury.

He told BBC News Online: "One thing we wanted to alert colleagues to is to make sure that if they are confronted with an injury from a mountain bike they should prepare for significant trauma.

"We do not want to put people off mountain biking, but we do want to get people to make sure they are protected."

Mountain biking has become increasingly popular over the last 10 years.

Surgery

It was an Olympic sport in Sydney last year and the British Cycling Federation estimates 10,000 people compete on a regular basis.

In 1998 off-road cycling was the third most popular leisure activity in the US, with 8.6m "off-road" bikers - double the number in 1993.

The area around Shrewsbury is a centre for mountain biking.

The 84 patients studied were aged between eight and 71, though the average age was 22. They had received 133 injuries between them.

Three-quarters were male and injuries were most likely to occur in the later summer months.

Half the injuries were fractures, mostly of the collar bone and shoulder.

'Dangerous'

A quarter of the patients required surgery, several patients needing more than one operation.

In the research paper, published in the British Journal of Sports Medicine, the authors wrote: "To date, no deaths have been recorded in our series, but, given the nature of the forces involved and the energy imparted on impact, future mortality in this continuing analysis is expected.

"Off-road cycling often involves travelling at speed down steep often unpredictable inclines and through loose narrow tracks covered in loose stone.

"It is the excitement of this unpredictable and dangerous challenge that motivates the predominantly young male participants, and it is not surprising therefore that both the experienced and the inexperienced rider will frequently fall.

We'd remind all mountain bikers to always wear a helmet as a bare minimum

British Cycling Federation

"Such accidents may be high energy in nature and may result in serious injury."

Previous studies in the US and New Zealand have shown few head injuries amongst mountain bikers because most wear helmets.

But the Shrewsbury study found 10% of injuries were to the head and neck.

A spokesman for the British Cycling Federation said: "We'd simply remind all mountain bikers to always wear a helmet as a bare minimum.

"We'd also recommend that riders never venture off-road alone and always tell someone where they are going.

"Finally, we'd advise all cyclists to join one of the national cycling organisations."

Research is being carried out into the effectiveness of body protection, though the BCF said it could be impractical for some forms of mountain biking.