The table below shows that horses have a huge advantage over us-humans, which allows them to use oxygen in an efficient way. Despite the physiological advantages horses have got, humans have got a biomechanical advantage over horses. There is a U-shaped relationship between the energy and speed in walking and trotting horses . This relationship allows horses to travel very economically at their optimal speeds but slows them down when they walk and run. In humans, energy is independent of running speed compared with horses. It makes humans not economical at their optimal running speed when all muscles try to perform at the same level.