They’re among the most studied individuals on the planet, so unique in their circumstances that an exclusive branch of medicine has been devoted to them, indeed a new subcategory of physiology itself. Their experiences teach us about the fine delineations of human biology – as well as its inherent vulnerability. I’m talking about astronauts, whose explorations on behalf of humanity take them far beyond the landscape of earth and the natural conditions of human life. We read about their pioneering endeavors. We see the spectacular images, possible because of their labors. Yet, we know little of their experiences and the physical struggles they endure in the name of discovery.
To us, they might seem the epitome of vitality and enthusiasm as they wave their greetings from space or upon return from their voyages. Truly, these men and women must love what they do. They must value the extraordinary work of space travel – both its inquisitive human quest and the resulting technological possibility. They bring more than heart and soul to their endeavors after all. Their bodies bear the brunt of profound adaptation few of us can envision, harsh acclimatization unimagined until a few decades ago in human history. Truth be told, we’re only beginning to understand the multifaceted adjustment space travel induces – the short term challenges and sometimes permanent emblems of living beyond the bounds of human habitation.
Upon leaving earth and entering what’s known as microgravity, the body processes the cues of its new environment and the physical demands within it. Without substantial gravitational pull, fluids shift toward a concentration in the upper body, and in the early days of a mission diminish by almost a quarter of total volume. Blood flow slows as does the distribution of nutrients. It becomes more difficult for the body to regulate blood pressure and maintain a consistent heart rate. The heart muscle slowly weakens in the face of lesser demand.
Without the anchoring effects of gravity, a sense of balance is difficult to achieve. At least half of astronauts experience a period of spatial disorientation, nausea, and headache  in what’s known as Space Adaptation Syndrome. As circadian rhythms are thrown off, sleep becomes difficult and subject to frequent disruption. The immune system becomes depressed, although scientists are still searching for the exact cause . Research shows that in a zero-gravity situation, the body doesn’t turn on the majority of genes related to T-cell activation. (The only other physical condition with this significant an impact on T-cell process is HIV infection.)
In a feat of efficient adaptability, muscle and bone deftly respond to the decreased demands of the physical environment. Without the weight-bearing exertion induced by gravity, the body’s muscles devote fewer resources to producing muscle-building proteins. Experts have measured the loss at approximately 2% per week . Higher cortisol  levels measured during space travel also likely contribute to breakdown of muscle.
The orchestration of bone formation and break down also shifts in response to the lower physical demand. Bone producing osteoblasts curtail their activity while the natural break down and recycling activities of osteoclasts ramp up. Measurements vary from individual to individual, mission to mission; however, bone density loss has been calculated between .6-5% per month. Astronauts who live on the International Space Station for six months showed losses of up to 30% of their bone density.
In an attempt to ameliorate the dramatic impact of space travel on human strength and well-being, experts around the globe have designed an evolving series of interventions. In response to the immunosuppressive effects of space travel, astronauts go through a partial pre-flight quarantine lasting 7-10 days. During the mission, they exercise 2 ½ hours a day 6 days a week on a stationary bike, a treadmill (strapped to the machine), and the specially designed ARED (Advanced Resistive Exercise Device) that creates load in the microgravity environment using vacuum cylinders.
Because their workouts, however carefully crafted, don’t offer the same protective benefit to bones as it does to muscle, researchers and space physiology experts have recently experimented with the use of vibration plates  as a supplement to astronauts’ fitness regimen. Some NASA scientists suggest that in addition to vigorous, high load exercise, the “low magnitude, high frequency” stress we put on our musculoskeletal structures just in positioning activities like standing or sitting put growth-stimulating demands on our bones. The vibration plates subject the individual to the high frequency signal that mimics these gravity-related positioning demands.
Upon return from space, astronauts participate in 4-12 weeks of rehabilitation to counteract the muscle and bone loss experienced during their mission.
Although the general processes of bone production and break down resume upon return to earth (to a certain extent reclaiming most losses over several years) the thinning of trabecular bone (found in the vertebrae and around the meeting points of bone in joints and sockets) may not recover . Because trabecular bone is built upon an intricate lattice-like structure, damage to the fundamental structure undermines the overall strength of the bone and leaves the person more susceptible to fractures in his/her lifetime.
What can we learn from these brave individuals who knowingly choose to be thrust into an environment that will wreak havoc with their most essential functioning?
That our own plight, in a sense, isn’t so different.
While the astronauts orbit above us, most of us earthbound creatures exist – either by choice or circumstance (unwittingly or otherwise) – in conditions nearly as alien. We also live as fish out of water, physiologically disoriented and separated from the conditions we need to thrive. And when we peek into the life of a space voyager we see our own, as we too attempt to mimic ideal environmental conditions and give our bodies what they need to prosper. While we don’t have to contest with microgravity, air pressure and oxygen abundance, we’re faced with our own set of challenges (see food , fitness , stress , sun exposure , etc.). For without just the right conditions, profound, and in some cases irreversible, damage follows closely behind.
This world and all of its characteristics – was the cradle for our unique and elaborate development. Although modern life distances us from many of our most fundamental, primal conditions for flourishing, the roots of human vitality remain the same as many millennia ago. Our humanity offers us astounding cognitive and imaginative ability. Yet, the blueprint for our physical progress, our basic health and well-being – in which the grander dimensions of our humanity is fostered – is embedded still in our most primal patterns. (If you don’t know what these patterns are yet, you have some reading to do !)
What say you readers? What other morals are there to this story? Thank you for reading!