– Xochielt Sanchez
Answer by Clayton C. Anderson:
That's an easy one to answer… and trust me, Garrett was hugely excited to grow any amount of inches in space!
On earth, our bodies are "slaves" to the force of gravity each and every day. I am six feet tall, and the gravitational tug keeps me that way, acting through my center of gravity all the way to the earth's center, keeping my spine in order, compressing my vertebrae/disks ever so slightly, allowing me to walk erect. In space, we are under the influence of micro-gravity, where the gravitational force is reduced considerably… on the order of 1/100,000! So, that "tug" is much, much less.
Our bodies are quite flexible. Muscles, ligaments, joints… they all have a margin of flexibility. When we live and work in micro-gravity, the reduced pull on our spine allows us to "grow" a little bit. It varies with each astronaut, but I grew almost two inches while living on board the International Space Station (ISS) for 5 months in 2007 and again for 15 days in 2010. The muscles stretch and the disks expand, ever so slightly, leading to a bit of increased height, but also –more often than not– increased back pain. As the back/spine muscles stretch, the body is placed into a configuration it is not used to, so think of the pain as similar to what happens when you strain a muscle on earth.
In order to combat this sensitivity, my Russian crew mates and I would simply compress our spines by pushing with our arms on the ceiling and our feet against the floor. Doing so for about 3-5 minutes went a long way to relieving any pain we (or at least I) experienced. While sleeping, the pain could also be present. If it was bad enough to wake me up, I would unzip the front of my sleeping bag about half-way down to my feet. Then, since I didn't weigh anything, I could bend my knees and rest them in the "V" of the sleeping bag's zipper, putting my body in the "fetal position" I loved so much as a baby.
This helped to stretch the muscles in my lower back very gently, bringing additional relief. So compressing and stretching the spine muscles and joints gently over time went a long way toward eliminating any soreness.
Keep lookin' up!