Dogs do it. Horses do it. So why don't humans? When animals need to get somewhere in a hurry, they gallop, but people rarely use this gait—similar to skipping, with the same foot remaining in front throughout the movement. To figure out why, researchers sent volunteers down a 30-meter runway at a run and at a gallop. Sensors placed along the track measured the force of their legs against the ground, while a motion-capture system—similar to what's used in digital animation—recorded their movements in three dimensions; researchers made an animated model (above) for each trial in order to calculate the forces involved . A separate experiment tested how much energy each gait required through 4-minute intervals on a treadmill. In an upcoming issue of The Journal of Experimental Biology, researchers report that galloping makes the hips move and absorb forces differently than a run does , and eats up more energy as a result. The front leg pushes the body up into the air while braking against forward motion, acting like the pole in the pole vault; the back leg does the opposite. A horse can shift energy between its front and back legs and their large tendons, making the gait much more efficient than a trot—the quadruped equivalent to a run. Hip strain itself might also prevent two-leggers from taking up galloping as a workout; treadmill gallopers reported that the gait was challenging and uncomfortable for hips and thighs, and several stopped galloping before the 4 minutes were up.
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