When astronauts are in zero gravity, or micro gravity, their muscles relax and without enough exercise their body parts can go numb and stop working. A simple solution is to exercise by stretching out your muscles, and exercise a lot. I've created a stretchy tube with two blocks attached to it's ends to help astronauts exercise their arms. You are meant to hold each of the blocks with each of your hands and pull apart, so as to stretch your arms, and keep them healthy. The 3D design is hollowed out, so as to make it more stretchy and save materials.