Studying how primitive man learned to walk upright, say researchers in the College of Engineering at Oregon State University, Corvallis, could lead to improved prosthetic lower limbs. Their findings outline a specific interaction between the ankle, knee, muscles, and tendons that improve understanding of how a leg moves forward to maximize motion with minimal energy.

Going forward, a more complete grasp of these principles could lead to walking or running robots or exoskeletons that are more agile and energy-efficient than anything that exists today. They explain that current robots don't walk like humans, as they lack an efficiency of motion and agility.

Researchers have long observed some type of high-power "push off" when the leg leaves the ground, but didn't really understand how it worked. This study concluded there are two phases to this motion: an "alleviation" phase where the trailing leg is no longer supporting the body mass, and a a "launching" phase where the knee buckles to allow a rapid release of stored elastic energy in the ankle tendons.

They calculated that muscles are insufficient for generating that powerful push off, so they looked for a power-amplifying mechanism. They explain that the coordination of knee and ankle is critical to swing the leg, but does not add large amounts of energy to the forward motion.

Current walking robots may use force to "swing" the leg forward from something resembling a hip point, but it's neither energy-efficient nor agile. And for more widespread use of mobile robots, energy use is crucially important, they say.