Although Alberto Minetti, a biomechanicist from the Institute for Advanced Biomedical Technologies in Milan, Italy, had spent years investigating human locomotion, he never bothered with skipping--until he studied galloping horses. When Minetti analyzed the motion of a galloping horse's front and back limbs separately, he found an uncanny similarity to skipping. In each gait, both limbs leave the ground. Then the trailing and leading feet land in rapid succession and push the body into the air again. As it turns out, though, says Minetti, while the mechanics of the two gaits are so alike, their effects on the body are very different.
In horses, galloping is a fast and energy-efficient gait. In humans, however, skipping is slow, jarring, and a waste of energy (the knees don't help generate any force). But skipping, while inefficient here on Earth, seems to have advantages elsewhere. "The Apollo astronauts practiced with several gaits on the moon--walking, loping, hopping, and skipping," Minetti says, "but skipping was the preferred gait." Skipping seemed to provide the right balance of exertion and stability in a low-gravity environment like the moon.