Human runners use hills to improve both cardiovascular capacity and muscle strength. Uphill climbs improve oxygen intake, and downhill descents increase muscle size and strength. As a runner moves downhill, the quad muscles absorb body weight and lengthen to control the descent. This type of muscle action is an eccentric contraction. Researchers have learned that, through training and over time, eccentric contraction creates a more efficient and less-injury-prone runner.

Does the same hold true for horses? James H. Jones, DVM, PhD, and his colleagues from the Japan Racing Association recently tried to answer this question by studying the cardiorespiratory responses of five Thoroughbreds as they worked on a treadmill set to varying speeds as well as degrees of incline and decline. They measured stride frequency, stride length, and cardiopulmonary and oxygen variables to determine how much energy the horses were exerting.

“Our hypothesis had been that the energy savings going downhill would be equal, but opposite of the energy cost going uphill,” he said.

However, the team found that “the amount of energy it took for a horse to travel downhill was only half of the energy used to go uphill,” Jones said. “This difference may be due to the eccentric contractions of the muscles reducing the cost of downhill locomotion