What is the average top speed of a American quarter horse?

For generations of horses now the American Quarter Horse has been bred for speed and sprinting. This breed has what is known as "quick twitch muscles". This makes for a good sprinter, Excellent corner turner, and 'stop on a dime' ability. The quick twitch muscles are different in the way the electricity is fired into the muscle itself. And it is what makes this breed one of the most versitile on earth.