What exercise can you do in zero gravity?
There are several exercises that can be done in zero-G, any of which you can do here on Earth.
"Isometric" exercises, in which you use one muscle in opposition to another, require no equipment and can be done anywhere. Here's an example; press your two hands together. Push HARD. Relax. Push; relax. This is an "isometric" exercise, meaning "same movement". Here's another; Place your left hand on the inside of your right knee, and the right hand on your left knee. Use your arms to push your knees apart, and use your legs to pull them together. Or, reach down and grab your chair, and PULL yourself down into the chair. (Please DO NOT do this one in the seat of a fighter jet, as you might accidentally grab the alternate ejection seat handles!)
Other exercises that can be done on Earth or in zero-G involve flexing against a bungee cord or large rubber band, or using a resistance device like a rowing machine or a stationary bike.
No. Gravity is a force with unlimited reach. Gravitys grip-force decreases with an increase in the distance between bodies. In a nutshell, there is no zero gravity, but there is very close to zero gravity. In the deep space between and at extreme distances from any galaxies we find what is effectively zero gravity.