Our bodies are Electromagnetic Spiritual Energy!!! Gravity is Electromagnetic" Energy. Only Electromagnetic "Gravitational Resistance" Energy makes "Muscle" in our bodies. So if it is exercise equipment "you can use without Gravity resistance"; (if you could use it in outer space) it does not make muscle. At the most it may firm your muscle some, but not "Make Muscle". If you trained using Gravitational Iron Weight Resistance you would build muscle. Then, if you switched to an Isometric Tension Bow, Spring, Rubber Band, Gas Shock or Shake Weight resistance exercise equipment, you would LOSE all the muscle you made training with Iron Weight Gravitational Resistance.