In continental Europe all harness races are conducted between trotters. A trotter's forelegs move in unison with the opposite hind legs -- when the right foreleg moves forward so does the left hind leg, and vice versa. In Australia, Canada, New Zealand, the United Kingdom, and the United States, races are also held for pacers. Pacers' forelegs move in unison with the hind legs on the same side.
Standardbreds have shorter legs than thoroughbred race horses and longer bodies. They also are of more placid dispositions, as suits horses whose races involve more strategy and more re-acceleration than do thoroughbred races.