I KNOW nothing about the technique of horse-racing, and there may be subtle reasons, or prosaic ones such as not desiring to break the horses' legs, why jockeys should not let their horses go too fast downhill. If, however, they were human and not equine runners, I should certainly say go faster downhill and slower uphill; at a guess, but I have not tried to work it out, I should say let them exert total energy at the same rate throughout the race. They would require less energy to run at the same rate downhill and more energy to run at the same rate uphill; so at a constant rate of energy expenditure they should go faster downhill and slower up.