In 2009, Usain Bolt reached the top running speed recorded by a human, of 44.72 km/h (27.78 mph) at the World Championships in Berlin.

However, he was not being chased by a bear. If he had been chased by a bear at the World Championships, we can assume his speed would have been even higher. There is science to back up this assertion. Individuals chased by bears (or other frightening predators) release adrenaline, which is a natural performance enhancing drug. In fact, artificial adrenaline is banned, because it boosts athletic performance.   

The adrenaline produced by flight from bears is natural and organic, and would not result in disqualification. However, we do not advocate adding bears to athletic competitions.