When John Glenn returned to space, he was at age 77 the oldest person to contend with weightlessness.
Weightlessness is the state of gravitational forces toward zero gravity. With zero gravity, the force of the pull of the earth on the body is equal to the force pulling the body away from the earth. Space crews now and space travelers in the future will be exposed to the short- and long-term effects of this phenomenon.
With weightlessness, there are multiple effects, including:
- Decrease in heart rate
- Decrease in respiratory rate
- Loss of body weight
- Changes in bone calcium
- Redistribution of body fluids with greater amount in the upper body
- Decrease in muscle tissue
- Weakening of veins and arteries in the legs
- Underproduction of red blood cells leading to anemia
From long space flights, we have learned that the body in space needs a little over a month to get used (acclimated) to these changes. Intermittent physical exercise can markedly improve the situation.
Once back on earth, the majority of these changes vanish and most matters revert to normal But there is nonetheless an initial period of weakness and difficulty with balance back on earth that may last several days.
The loss of calcium from bone, however, is a more serious problem, particularly during and after long space flights. The physical stresses on bone and pressures from weight bearing that take place in the presence of gravity are quite clearly necessary for the normal formation, remodeling, and maintenance of bone. The impairment of these normal bone processes in space leads to liberation of calcium from the skeleton. The result is weakened, brittle bone that easily breaks. This process is quite similar to the osteoporosis that occurs on earth. And, just as with osteoporosis, full recovery of bone structure may not always be possible.
The physiologic changes encountered in space travel provide an example of how humans adapt to their environment. The human body was not designed to board a rocket for a long flight to Mars. Yet we adapt. Or, if need be, we adapt the conditions under which we live in space.
AeroSpace scientists are working on ways to travel better through space, including ways to prevent continued bone loss and ways to allow us to match the natural conditions on earth. Among the beneficiaries of this research and development was in October, 1998 be John Glenn.
For more information on the effects of weightlessness and space travel, check out this website, http://www.nsbri.org/