The International Olympic Committe (IOC) have revealed they will be forced to postpone high profile events such as the marathon, road cycling and the triathlon at this year's Olympic Games if pollution in Beijing does not improve.

The admission that the IOC will devise what a 'plan B' for some endurance sports comes a week after Haile Gebrselassie, the marathon world record holder, said he was unlikely to compete in the event at the Games because of worries over how the conditions would affect his asthma.

An IOC medical commission investigation into air quality in Beijing in August last year found that the health of athletes was "largely not impaired" by the conditions expected over the same period this summer.

The report also noted that competitors at the World Junior Athletics Championships in August 2006 reported no problems.

However, the commission has conceded there will be some risk to competitors in endurance events "that include minimum one-hour continuous physical efforts at high level - urban road cycling, mountain bike, marathon, marathon swimming, triathlon and road walk".

The risk is deemed high enough for the IOC to begin working on "procedures which will allow a 'plan B' to be activated for such events if necessary". Air quality and weather conditions will be monitored and events could be postponed but a change of venue is not mentioned as a possibility.

"It may be that some events will not be conducted under optimal conditions - which is the reality of sports competitions - and that we may not see records broken in Beijing," Arne Ljungqvist, chairman of the IOC medical commission, said.

"However, the Games are more about competing in the Olympic spirit than about breaking records. For a few sports where we do see a possible risk, we will monitor the situation daily during Games time, and take whatever decisions are needed at the time to ensure the athletes' health is protected.

"The IOC is confident that measures already put in place, plus those planned by Beijing organisers and city authorities, will continue to improve the city's air quality leading up to and during the Games."