Blog written by Dr. Joan Vernikos, InnovaSpace Advisory Board Member, former Director of Life Sciences NASA,
Founder of Thirdage llc, Culpeper VA, USA
The influence of gravity in human health on Earth has been grossly underestimated. Only through the experience of human spaceflight some 60 years ago did it become apparent that changes induced by living in the microgravity of space were not simply due to inactivity, as was originally thought. Unlike other variables like heat, cold or altitude, there is no evidence that the human body adapts to living with less or no gravity.
In fact, the longer humans are in space the faster the degenerative changes seem to occur, despite significant exercise and attempts at other countermeasures. With durations lasting six or more months and better diagnostic techniques, it can be seen that living in space accelerates tenfold the rate of decrease in bone density, when measured over the same time in the average population on Earth.
On Earth the effect of gravity is fairly straightforward. It pulls in one direction only, downward, towards the center of the Earth. Unlike plants, humans have the choice of orienting themselves relative to the force of gravity in every conceivable way and mostly in intermittent patterns. They also reduce gravity’s effects on the body during sleep at night or in continuous bed-rest when they are lying in bed. They can also enhance its force with various activities such as walking, running, jumping, bouncing on a trampoline or riding on a centrifuge. How we sense and use gravity determines our health and fitness. The most evident is that of loading, which imparts weight to the body when gravity is pulling in the head to foot direction (+Gz). We are aware of exertion against the force of gravity during normal activity of moving and walking. Gravity is obviously involved in postural and other changes in movement and direction, such as giving cues about our spatial orientation relative to gravity’s vertical pull. Without regular exposure to these +Gz forces, as occurs during spaceflight and prolonged bed-rest, significant cardiovascular, musculoskeletal, metabolic, neural and primarily neuro-vestibular mediated functions are compromised.
Metabolism is changed, with fat accumulating to replace lost muscle and fatty oxidation with a reduced capacity to use fats for energy. In addition to metabolic changes, intermittent exposure to centrifugation mimicking alternating standing and sitting, draws fluids to the feet resulting in secondary increased heart rate, blood pressure, stroke volume, baroreflex sensitivity, increased blood volume and an altogether better functioning cardiovascular system. Centrifugation, as with an intense exercise bout, would probably lead to an endothelial ‘nitric oxide dump’ that would benefit blood vessel responsiveness. Both in space and ageing, endothelial lining atrophies with resulting vascular weakness. Centrifugation has also been found to improve parasympathetic nervous system function as well as brain blood flow and oxygen saturation, all desirable features of improved health and brain function.
A gravity stimulus may be provided in the form of a rotating short-arm centrifuge. Accepting that ageing is primarily a Gz-deprived condition, then it follows that gravity therapy would be a logical treatment during ageing or as a preventive measure in other degenerative conditions or injuries.
If these are caused or worsened by gravity-deprivation then it stands to reason that gravity replacement or treatment should provide relief. These include:
However, relatively little is known about how much and when such artificial gravity is optimal in humans. Studies in animals - rats, mice, rabbits, chickens –were exposed to 2G, 24h/day for 20 days with a short daily stop for cleaning and feeding. Such chronic exposure to 2G resulted in reduced food intake, loss in body fat, increased muscle and bone mass and strength, reduced insulin levels and insulin resistance. On the other hand, human studies have followed the exercise once-a-day custom, and used centrifugation only once a day at levels varying from 0.5 to 1G, however, these once-a-day protocols have proven to be only partially beneficial.
A twice or three times a day G-exposure would come closer to the ideal G stimulation we are exposed to as we move around and change posture throughout the day. In research that I and my colleagues conducted (published 1996) involving volunteers deconditioned by lying in bed continuously, we tested the effect of the 1Gz stimulus of standing up for 15 minutes every two hours throughout the 16-hour day. This schedule was completely effective in maintaining aerobic conditioning, blood volume, cardiovascular responsiveness, and preventing calcium loss from bone, whereas standing up for this time period every 4 hours was found to be less effective.
Clinical applications of Gravity therapy could include, but are not limited to :-osteoporosis, accelerated repair of bone fracture from sports injuries, in the elderly or paraplegics, less insulin resistance in diabetics, increased muscle mass in conditions of muscle wasting, joint deterioration aggravated by weight bearing and potentially certain forms of pulmonary edema or concussion.
What is undoubtedly true is that for many of us our modern lifestyle does not provide the level of activity of our parents and grandparents. We have struggled for decades to exercise more and eat less, but one thing hasn’t changed: we still spend hour after hour each day virtually immobile in our chairs. Our lives have become sedentary and the way we live affects, not only our physical health, but our emotional and mental wellbeing. From the more complex perspective of exercise equipment or centrifuges, to the more everyday and accessible activities that everyone can incorporate into their daily lives, such as simply standing up every 15 minutes or taking the stairs instead of the elevator, using gravity in our favour and as a therapy will become more and more important as we age, helping to maintain the balance and strength we need to continue performing basic life functions.
“There is much that is not known about how gravity is sensed and translated into input to every system in the body. This includes its required threshold, frequency, intensity, duration and direction. Space provides the ideal environment to tease out these aspects of gravity. This is crucial so that we may understand the requirements for replacing gravity in the countermeasure formula for exploration missions as well as expanding our knowledge in basic human physiology on Earth.”