Figure 1. The Power Tower initiates negative geotaxis in Drosophila.

A. The Power Tower in its resting position. The lower tier of the Power Tower contains vials with the foam stopper pushed down to prevent any running. The vials on the top tier have the foam stopper up, which allows the flies to run. B. The rotating arm presses down on the lever, which elevates the Power Tower platforms. When the rotating arm releases the lever, the platforms drop, which knocks the flies off the sides of the vials onto the food. After the platforms drop, flies begin to climb. C. Flies in the exercised group go on the machine with their foam stopper up (right), while flies that are unexercised have their foam stopper pushed down (left).