A butterfly's secret to long life  January 2013

Why humans don't gallop  January 2013

January 2013  
Why humans don't gallop
by Cameron Walker

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.