Discoveries

January 26, 2023

It’s Complicated

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Walking looks very simple. It’s not.

Part of the reason it’s complicated in humans is because of the shape of the foot – an oddity in the animal kingdom – and our strange gait.

When walking, people exhibit a “double-bounce” walking pattern: The first bounce helps the foot absorb the impact of the body’s weight as it hits the ground. The second one’s purpose, though, scientists haven’t understood – until now.

Recently, biomechanists determined that the second bounce is an energy-saving technique that allows humans to walk by prioritizing endurance over speed, Wired Magazine reported.

In their paper, researchers simplified the foot-leg system to just the four joints at the hip, knee, ankle and toes in order to model the physical forces that propel the double-bounce.

They used data collected from 21 people walking on a treadmill and described the foot’s heel-to-toe stride as if it were a simple object rolling on the ground.

The findings showed two competing factors that influence the foot’s movement: The force of the upper body holding it fixed to the ground, and the torque of the ankle attempting to rotate the leg into swing.

The team explained that as long as the force of the upper body is larger than the ankle’s torque, humans can stay upright. But the longer this occurs, the harder the ankle works to overcome it, resulting in generating enough power to thrust the leg forward – in the second bounce.

Researchers suggested that this energy-saving technique was evolutionarily advantageous to our human ancestors because it helped them walk for longer periods without getting tired.

They also believe that understanding the second bounce can help improve prosthetic and robotic designs, and provide insight into the evolutionary stresses our ancestors experienced.

This story originally appeared in the January 26, 2023 newsletter, The Morning After.