Physiological Effects of Microgravity

Abstract

The microgravity state as a research environment is also of interest to life sciences, i.e. the whole body of researches in medicine, biology, zoology and botany, studying the influence of gravity on living organisms, including the human being. In this chapter we limit ourselves in giving some general considerations on research in human physiology during space flights and in microgravity. The main physiological effects caused by microgravity are presented, grouped in four classes: (1) perturbations of sensorial systems related to balance, orientation and the vestibular system; (2) modifications of bodily fluid distribution and their impact on the cardiovascular system; (3) effects on metabolism and bodily functions; and (4) the adaptive processes of muscular and skeletal systems and their pathological consequences. Bone demineralisation, one of the most debilitating effects of microgravity, is addressed in more details. An application of space medicine research for osteoporosis prevention is presented in the last appendix.

Appendix 13: An Application of Space Medicine Research

A spin-off of research on prevention of astronaut bone demineralisation consists in the preparation of a programme of simple physical exercises that is prescribed to women after menopause to avoid fractures due to osteoporosis. Statistically, a woman out of ten will suffer during her life from a femur neck fracture. This frequency is doubled after menopause. After the age of 60, 20% of female patients will decease and half of surviving will be handicapped. It is therefore of paramount importance to understand the functioning mechanisms of osteoporosis and bone fragilization.

On the other hand, preventing consequences of fractures due to osteoporosis, if possible at all, has an obvious economical character, as post-menopause fractural osteoporosis is an important and costly public health problem.

Weightlessness is creating a fast evolution model of bone loss, space research in microgravity on bone pathology can contribute to better understand fundamental mechanisms of osteoporosis. Programmes of preventive physical activity based on acute osteoporosis as observed in microgravity are derived from astronaut training programmes.

So, some French specialists recommend the following types of exercises (always under medical supervision!). Exercises with vertebral extension are recommended, those with flexion are to be avoided. Exercises should be done while under load (walking, running, stair climbing) and should not be necessarily done every day. A programme of moderated exercises (jogging, exercises while standing, lying down or sitting during an hour, twice a week) would already yield an increase of minimal content of vertebral bone. An hour of walking per day during two years would reduce by half the frequency of osteoporotic fractures.

Thus, one very logically recommends to sport to stay in good health!