As a flight surgeon and specialist in space medicine, I have awaited my own space flight experience with great anticipation. I have spent years practicing the craft of space medicine, studying the world’s literature and debriefing crew members following their flights. The prominent topics on my mind have been the specific physiologic problems associated with living in weightlessness – bone and muscle loss from disuse atrophy, cardiovascular deconditioning, neurovestibular reprogramming, etc. I have often said that humans essentially become extraterrestrials in space due to the global multi-system changes that define adaptation to weightlessness. Many physical and laboratory norms shift, and medical problems may present differently against this backdrop. But after 100 days on orbit, what has struck me most is the constellation of fundamental changes in behaviour and motion associated with deep adaptation to weightlessness. Learning to live and work here prompts a metamorphosis of sorts in habits, body awareness, motion control, and hygiene. This is in concert with a remote, expeditionary lifestyle with somewhat sparse provisions, which rather reminds me of being at sea. In some ways we degenerate as compared to what people expect. Let me paint a picture.
The neutral body posture assumed in weightlessness represents the sum resting flexion force of the major postural muscles. Put simply, you assume a posture somewhere between standing and fetal. You have to make a conscious effort to ‘stand straight’, and it is actually uncomfortable to be restrained out of this position for long periods. Shrug your shoulders and let them fall a little less than half-way, then keep them there. That’s us, a posture your mother would never approve of. As for your feet, as my Air Force buddies often remind their Army counterparts, we don’t walk; we fly. The calluses on the soles of your feet slough, part of the process we call the mid-mission molt, giving the word tenderfoot a new meaning after return to earth. Inflight, you go around in stocking feet or barefoot (my preference), and the prehensile nature of the toes rises to the surface. Your feet are used to stabilize the body, allowing you to fix yourself into position to optimize your work envelope, and toe holds are a key part of this. Calluses develop on the upper surface of the feet due to contact with foot restraints, particularly the dorsal aspect of the 1st metatarsal-phalangeal joint.
In weightlessness, every structural surface is used for work and stowage. The concept of walls and ceiling is a very gravocentric construct which we don’t have up here; we change this orientation frequently, sometimes appearing to be hanging from surfaces in the camera views. It has been surprisingly easy and natural to develop the three dimensional spatial awareness to work and move through the ISS, changing orientations quickly and frequently in the course of normal work. And finally, opposite our terrestrial counterparts, up here we locomote with our hands and arms, carrying big loads with our feet and legs.
Add a few behavioral changes that abound up here – letting hair grow, playing with food, and singing primitive chants – and I give you Cosmopithecus
. The physiological changes I mentioned are certainly prominent but reside at a deeper level, most below a threshold of appearance or detection without medical imaging, biochemical analysis, or provocative physiologic testing. On the surface that extraterrestrial I have been describing for years is a hunched over, fast flying, spatially versatile creature that functions naturally in 3 dimensions. The pace of work here is quite brisk, and as you might guess the pressure to execute the plan without errors is high. The picture painted is the sum of several forces that result in an efficient worker in the weightless environment. And if there is any doubt, it is tremendous fun up here!