Mountain bikes may look good but not all meet the demands of rough terrain cycling, according to research by safety specialists at Nottingham University.

Commissioned by the Department of Trade and Industry, which was concerned that accidents involving mountain bikes increased by more than 300 per cent between 1989 and 1992, engineering and ergonomic experts from the university's product safety and testing group have completed a 15-month study of all the mountain bikes - properly known as all terrain bikes, or ATBs - on the market.

A testing programme involving 70 skilled ATB riders and around 500 recreational riders found that while many bikes look suitable for speeding up a Lake District fell - they sport chunky tyres, thick frame tubes and straight handlebars - they are actually extremely dangerous. Further examination involving laboratory simulations confirmed this finding.

Test bikes were fitted with up to 30 strain gauges at 15 points on the frame and forks.

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Some damaged easily, especially around the forks and tubes. Engineer Richard Cobb said: "Safe performance is not exactly associated with price, but it is true that certain of the cheaper ATBs would not withstand some of the expected impacts when ridden off-road." ATB-style bikes can be purchased for as little as Pounds 100 while the genuine article can cost as much as Pounds 5,000.

The more expensive bikes boast frames made from titanium alloys and carbon fibres, which are lightweight but strong. The less expensive bikes are made from heavier steel.

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Other differences, which can affect safety, include the quality of components like gears and the method of fixing the individual parts of the bodywork.

The researchers also examined rider behaviour. Ergonomist John Wilson, who headed the project, said that many cyclists attempted stunts that either they or the bike were unprepared for - such as jumping over rocks and boulders, or racing down steep slopes and uneven surfaces without the necessary protective clothing.

He added that ATB-style bikes - as opposed to the real thing - had been bought because of the fashion for healthy outdoor pursuits and the fad for chunky products like Doc Marten boots and four-wheel drive vehicles.

The DTI's early intelligence unit is currently examining the research work and may recommend the introduction of a British standard for off-road bikes. ATBs have only to conform to road bike specifications at the moment. These present no problems for ATB or even ATB-style bike manufacturers.

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Professor Wilson said that the reputable manufacturers and retailers are looking to improve safety through labelling and warning requirements for different levels of ATB.