Prosthetic leg can 'change gears' to make going up stairs easier

A robotic leg with motors that work like bike gears could let a wearer walk up stairs – which many people find impossible with unpowered prostheses. Most prostheses have no motors to actively assist walking, but instead are either passive or help only by altering the resistance of a joint's swing, controlled by a low-power microchip. The few actively powered prostheses on the market are relatively heavy and bulky, with short battery lives, and have achieved limited success.