Humans Walk Weird. Scientists May Finally Know Why

Walking is a lot of work. First there is touchdown, when your foot hits the floor. The single support phase occurs when you are balancing on that leg. Your leg goes into a forward swing after you roll on your toes.

Researchers have known for a long time that when we walk, our planted leg bounces twice before we swing into the next step. The knee bends when the foot first touches down and then again just before the plane takes off. The second bounce can help our foot absorb the impact of our weight.

Scientists at the University ofMunich may have found an answer to a question in a paper published last month. They deduced that the double bounce is an energy-saving technique for a species that has long prioritized endurance over speed. They think their model can help improve the designs of robotic and artificial limbs.

Daniel Renjewski says the foot is the key element. In the animal kingdom, the human foot is sort of odd. Few other animals have an angle between the foot and the leg like people do. Most animals walk on their feet while we walk on ours. Human feet are relatively flat, and our legs are heavy, which makes staying upright while propelling the body forward a mechanical challenge. The foot is planted for up to 70% of a step cycle to help us stay balanced. Less time allows us to propel ourselves forward. When walking to recirculate the leg you have to work harder. Renjewski says that it seems odd to aim for a gait that leaves little time to swing your leg forward.

How does the human race get around? Our understanding of how we walk has been limited for a long time because trying to model what all of the muscles, tendons, and joints are doing at any given time is difficult. Renjewski and his team found a way to reduce the human walking gait to a single equation.

The researchers reduced the foot-leg system to just four joints. As a graduate student, Lipfert collected information about the forces and joint positions of 21 people videotaped while walking on a treadmill, and they tried to describe the foot's stride as if it were a simple object rolling on the ground. It's easy to understand the movement of the foot.