For something so routine, walking is shockingly complicated. Bio-mechanists break a single step into several phases: First there is touchdown, when your heel strikes the floor. Next comes the single support phase, when you're balancing on that leg. After that, you roll onto your toes for takeoff and your leg goes into a forward swing.
All of this contains a mystery. Researchers have long observed that when we walk, our planted leg bounces twice before swinging into the next step. That is, the knee bends and extends once when the foot first touches down, then again just before takeoff. That first bounce helps our foot absorb the impact of our weight as we hit the ground. But the function of the second bounce, a feature characteristic to human gait, has never been clear.
In a Physical Review E paper published last month, scientists at the University of Munich may have found an answer. By modeling the physical forces that drive our double bounce, they deduced that it's an energy-saving technique for a species that has long prioritized endurance over speed—which may be a clue about why humans evolved such an odd gait. Now, they think their model can help improve prosthetic and robotic designs, and may even lend insight into the evolutionary pressures our ancestors faced.
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