The formation of calluses on the tops of the feet, while in microgravity, are the result from the astronauts stabilizing themselves with the hand bars that are throughout the station. Callus itself is not a direct health threat to the astronauts, however it can lead to painful skin ulcers and infections.
Callus Voiding Grips are positioned directly on the feet to reduce friction and pressure from the hand bars; a lubricant can be applied between the grip and the feet to further reduce friction. The design of the grip allows for increased flexibility, while permitting perspiration to travel to the socks. Socks should be placed over the grip to prevent excessive movement of the grip.