Inclines, Declines, and Horse Energy Exertion

Horses' oxygen consumption and cardiac output decreased by an average of 24% and 9%, respectively, when going downhill.

Photo: iStock

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.”

Specifically, while the horses’ stride length and frequency remained unchanged, their oxygen consumption and cardiac output decreased by, on average, 24% and 9%, respectively when going downhill.

A similar previous study showed that horses, unlike humans, go slower when traveling downhill. The authors of that study speculated this was due to the horse’s larger body mass. They could use their legs to slow when heading downhill, while humans presumably take advantage of the gravitational potential energy to run faster.

“That is speculative, but sounds reasonable,” Jones said.

Further research is needed to determine if eccentric training induces skeletal muscle changes in horses similar to those in humans.

The study, “Cardio respiratory function in Thoroughbreds during locomotion on a treadmill at an incline or decline,” was published in the American Journal of Veterinary Research

About the Author

Katie Navarra

Katie Navarra has worked as a freelance writer since 2001. A lifelong horse lover, she owns and enjoys competing a dun Quarter Horse mare.

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