The accumulated experiences of staying in space for several months and the future possible interplanetary flights of the duration of a few years have made rise to important and hard questions regarding the human physiology and the study of zero-gravity body workouts. It is the Physiologist and the Sport Doctor’s ability to respond adequately to the astronauts needs. From the management of physical conditions in the spaceship, even after years in the space, to a prompt readjustment of the Earth conditions. During the time in space the body goes through many different alterations – which are similar to those that an elderly or disabled person experiences. Thus, the body needs the ability to readjust to the gravity force on earth.
Effects of zero gravity
Gravitational force on Earth, of which living beings are subject to, regulates in a significant way the functionality of all our body’s systems. The functioning of the cardiovascular and respiratory system, the distribution of body fluids in the various tissues and in the blood vessels, the bone structure and its ability to maintain the high mineral content, the muscle composition, the complex control of body movements, all of these have been for millennia influenced by gravitational force. Therefore, staying for long periods of time in space, in conditions of zero-gravity, causes a series of imbalances within the body.
Bones and the mineral metabolism
On land, the bones are constantly subject to the descaling and calcification processes. These are regulated by numerous factors, such as: muscle contraction and exercising. The maintenance of the upright position on earth is the result of continuous contractions of muscles, which prevent the body from falling forward. The muscles used for this are called spinal erectors (spinal muscles, the front of the thigh and the back of the leg.). Continuous muscle contractions, which are completely unnoticed, are necessary to hold the upright position. By causing continuous bone stress, the stress represents the stimulus for deposition of calcium. Physical activity more or less intense and the interaction of the daily life are a second vital stimulus. In space the upright position does not exist, same as long periods in bed or due to lack of physical movement (elderly, disabled, etc.) Bone loses its ability to regenerate, and the decalcification process (osteoporosis) prevails over the deposition of calcium minerals. After returning from space it can be months before the bone mineral content can recover fully, and this is not at all certain that it can happen after staying in space for long periods.
Muscle contractions, physical exertion, exercise, the movement against resistance, the same continuous contractions to stand upright allow the muscle to remain efficient. An increase in physical activity, the normal load to which the muscle is subjected, represent the stimulus to increase the muscle volume (muscle hypertrophy). In space, the absence of gravity does not require the maintenance of an upright position and muscle contraction takes place with minimal effort, unless in particular and rare situations. This entails a reduction in muscle mass of 20-30% already after a few weeks of permanence at a greater altitude, as well as the muscle mass tends to shrink on earth with advancing age, with a sedentary lifestyle and with disability conditions of any type. A loss of strength and more specifically of explosive strength (maximum strength), which requires a fine coordination of activation of more muscles, is associated to the reduction of muscle mass. After a year in space the reduction of strength and muscle power reaches 40-60% of pre-flight value. The recovery time, to return to normal state, seems to be longer if the duration of the flight is longer. Recent studies indicate that after 450 days of a flying in space, you need a period of one year for complete recovery even though the astronauts are perfectly fit and healthy. It is still uncertain what could happen in multiannual flights.
Heart and circulation
When standing on the ground, the force of gravity moves a considerable mass of blood in the lower limbs. In space there is a tendency for blood mass to accumulate in the large thoracic vessels. This situation, due to an innate reflex mechanism, causes an increase in diuresis. This is abundant for a few days, and consequently results in a decrease of blood mass, which subsequently settles at lower values of 10-20% with respect to what is found on earth. However, this does not cause any damage to the body. Heart and circulation appear to quickly adapt to the new condition of increase in gravity in around ten days. In fact, the pressures in the circulatory system are the same as that on earth, the heart rate remains substantially equal, and the work of the heart muscle, contrary to other muscles, is unchanged. The problem arises upon return to earth. In the first few days, upright posture is hampered by the phenomenon called “orthostatic hypotension”. The rise from suddenly standing on the earth, causes the blood to move in significant amounts in the lower limbs. This then lowers the amount of blood thrust towards the brain, this then leads to a sense of fainting that forces the person to again assume the horizontal position. This phenomenon is gradually reduced and disappears in the astronaut after about ten days.
Through pioneering research of YoYo ™, inventors Dr Hans Berg and Dr Per Tesch of the Karolinska Institute of Stockholm describe the effectiveness of the inertial flywheel technology. They found that fly-wheel technology provides a valuable tool for astronauts to maintain their physical and athletic condition. Because this technology does not rely on gravity, on hydraulics, or an external power source, technically it is the perfect equipment for exercising in space.