http://www.britannica.com/eb/article-9039306/harness-racing
Patricia: As a follow-on to my agreement with Robert’s answer, but more on a point of clarification and a little more technical. Harness racing: sport of driving at speed a Standardbred (q.v.) horse pulling a light two-wheeled vehicle called a sulky. Harness racing horses are of two kinds, differentiated by gait: (1) the pacing horse, or pacer, moves both legs on one side of its body at the same time; (2) the trotting horse, or trotter, strides with its left front and right rear leg moving forward simultaneously, then right front and left rear leg (on the diagonal).
The translation workplace 
peer agreement (net): +5