CNN's Dr. Sanjay Gupta tries out a vertical treadmill used by NASA in research to cut astronaut's risk of bone loss

Dr. Sanjay Gupta
CNN Chief Medical Correspondent

This week, I did a series of pieces about how astronauts stay fit in space. Sure, it was fascinating to be strapped into a system of pulleys and harnesses that effectively simulate weightlessness. It was interesting to be pulled up to a vertical treadmill or eZLS – the enhanced zero gravity locomotion system. And, yes, I got to be an astronaut for a day, experiencing firsthand what it may feel like to exercise in space. (watch video)
 
I learned that exercise in space, especially for those long missions, is essential for astronauts, not something you might do occasionally. It has to be comfortable to do and it cannot interfere with the function of the spacecraft. (read more)  More than that, though, I learned how beneficial gravity is for us on Earth. Doctors call it axial load. You can think of it as a slight tension on our bodies, more importantly our ligaments, tendons and bones. Turns out, this slight pulling of gravity slows down the loss of bone mass, which in space accelerates 10 times faster than a post-menopausal woman.

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