Tips on Horse Breeds
Different breeds are intrinsically suited to the type of work that they do. They are not limited by their will, or their desire, but rather by their physiological make-up, which is breed (i.e. genetically) determined to a large extent. Quarterhorses make good sprinters because they typically possess many power-lifter type muscle fibers, and thoroughbreds make excellent cross-country horses because they possess 'marathoner' muscle fibers.
For more information, please read the story What Makes a Quarterhorse Different from a Thoroughbred?