Interestingly, resistance training has been proposed as an aid to counteract quadriceps muscle atrophy in astronauts during extended missions in orbit. A study compared the "gold standard" squat using free weights and a non-gravity dependent flywheel resistance exercise device designed for use in space.

It was later found that the quadriceps muscle group showed greater results following flywheel squats compared with barbell squats. Collectively, the results of this study suggest that quadriceps muscle use in the squat is comparable, if not greater, with flywheel compared with free-weight resistance exercise. The data appeared to provide support for use of flywheel squat resistance exercise as a countermeasures adjunct during spaceflight.

Read the full study here.