Yun Seong Song, an assistant professor of mechanical and aerospace engineering at Missouri S&T, wants to make walking up and down stairs easier, so he created a device that recycles the energy we use to climb and descend.

The steps could be useful during post-surgical recovery. They could also help elderly people navigate their homes more safely and avoid falls.

“When walking down, the spring in the stairs acts as a cushion and brake,” says Song. “The gentle downward movement alleviates work by the trailing ankle, which is what keeps you balanced and prevents you from falling too fast on normal stairs. When going up, these springs help you by giving back the energy that was stored.”

The spring-loaded stairs compress when someone comes down the stairs, saving energy otherwise dissipated through impact and braking forces at the ankle by 26 percent. When going up, the stairs give people a boost by releasing the stored energy, making it 37 percent easier on the knee than using conventional stairs. The low-power device can be placed on existing staircases and doesn’t have to be permanently installed.

Each stair is tethered by springs and equipped with pressure sensors. When a person walks downstairs, each step slowly sinks until it locks into place and is level with the next step, storing energy generated by the user. It stays that way until someone walks upstairs. When a person ascending the stairs steps on the sensor on the next tread up, the latch on the lower step releases. The stored energy in the spring is also released, lifting up the back leg.