IT IS one of the fastest-growing sports in Scotland, but it is now emerging as one of the most dangerous.
A dramatic rise in the number of serious mountain bike accidents has sparked two safety reviews involving accident and emergency doctors and the Forestry Commission.
At one hospital alone, at least 10 casualties are treated every weekend as a result of cycling enthusiasts - many inexperienced - losing control and crashing into trees or rocks.
Scotland has become one of the world's top mountain biking destinations and it is estimated that tens of thousands take part in the sport every week.
But the Forestry Commission has ordered an inquiry after the upsurge in accidents at its Scottish properties. At the same time, doctors in Fort William, where the mountain bike World Cup will be held later this month, are carrying out an investigation into the rise in injuries.
Borders General Hospital - close to the commission's downhill resort at Glentress near Peebles - says it is now dealing with more than 10 mountain-bike-related casualties every weekend.
Injuries range from serious lacerations to major fractures and head and spinal injuries. Last month, a 45-year-old GP from Jedburgh broke his neck when he went over the handlebars of his bike at Glentress.
A similar pattern has also emerged at Belford Hospital, near Fort William. A spokeswoman said: "Staff have noticed they are getting more and more mountain-bike-related injuries. As a result they have taken someone on to conduct an audit of outdoor sports injuries."
Mountain biking has emerged from a minority pursuit into one of Britain's fastest-growing outdoor adventure sports. Tourism agency VisitScotland estimates that more than a million mountain bike excursions are now taken every year in Scotland.
The commission has seven sites - called the Seven Stanes - in southern Scotland, but has also opened trails at Aonach Mor near Fort William, Laggan near Aviemore, Fochabers in Morayshire and the Black Isle.
Safety campaigners say mountain bikers should be compelled to wear helmets and undertake basic safety training before being allowed to tackle potentially dangerous runs.
Scottish Cycling, the body that promotes the sport in Scotland, said the rising number of injuries was a "great concern".
Spokesman Colin Renton said: "Greater numbers of people are getting involved in mountain biking with very different skill levels.
"If you are a beginner skier you wouldn't tackle a black run. The basics should be taught before people are allowed on serious mountain biking tracks."
The safety review is being undertaken by John Ireland, a commission official involved in mountain bike trail construction for more than 20 years.
He will research whether sufficient safety information is being given to cyclists before they set out, and whether trails could be constructed or managed in a better way.
Cycling expert Richard Moore is concerned about how easy it is for inexperienced riders to take on difficult runs.
"The problem is that anyone can go and use the tracks, and you still see people going down them without proper helmets or proper bikes," he said. "There is no restriction on anyone using these trails."
Paul Taylor, a married father with two daughters, had only been mountain biking on downhill trails for three months when he attempted a jump and fell and broke his back. The 35-year-old former distillery worker from Carron, near Aberlour, is now paralysed from the chest down after the accident on a Forestry Commission run near Fochabers last year.
Taylor, who had to be airlifted off the hill to hospital, said riders should be forced to wear proper protective gear and be given more explicit warnings on the potential risks.
He said: "I was used to riding mountain bikes on trails, but not taking on big jumps and purpose-built drops.
"I tried to make it as safe for myself as I could by wearing a proper cross-country safety helmet - ordinary cycle helmets won't do. But when I came off, my head was OK but I injured my spine.
"Of course, it was my decision to take the jump, but there should be more warning signs and an escape route if you change your mind at the last minute."
In setting up mountain biking centres in the Borders, Dumfries and Galloway and the Highlands, the commission has played a central part in turning Scotland into one of the top five locations in the world for mountain biking.
Its Glentress Forest and Innerleithen sites, near Peebles, are now Britain's number-one destination for the sport, with visitor numbers doubling from 160,000 in 2003 to 330,000 last year. Across Scotland, more than 20,000 riders take part in the sport every week.
An A&E source at Borders General Hospital confirmed there had been growing numbers of mountain bike accidents in the last two years, mainly from Glentress and Innerleithen. "Before then we used to mainly get mountain bike injuries during the summer, but now it is right through the year," she said.
"People are wearing helmets, but even this is not giving them enough protection when they are hurtling down a track."
The commission believes the rise in accidents reflects the phenomenal growth in popularity of the sport, but it wants to make sure its safety precautions are as good as possible.
Alan Stevenson, head of recreation, said: "The review will build up our understanding of good practice and identify any weaknesses in the system."
Information leaflets ask riders to make sure they have proper helmets and appropriately maintained bikes, and are experienced enough to tackle the trails. "Trail-head signage is also very important, but the problem is that many people don't read it," Stevenson said.
However, the commission is not in a position to compel riders to comply with safety measures, he insisted.
"But if the review suggests there are improvements to be made, we will take action on it."