Muscle and Bone Physiology

Therefore over a period of time in microgravity the musculo-skeletal system adapts and changes; however this change is not uniform throughout the body and the way any region the musculo-skeletal system changes depends mainly on whether it is normally required to support the body’s weight on earth. On earth in a 1G environment, the bones and muscles of the legs and lower body are normally required to maintain an upright posture and therefore have to work against the force imparted by gravity on the body’s mass. This means that the musculo-skeletal system of the lower body tends to adapt to the removal gravity by losing mass and becoming thinner and less dense, as the additional tissue is surplus to requirements in space. Bones and muscles in the arms and upper body are not affected as much by space and microgravity due to the fact that they are not normally weight bearing on earth, and it has been reported that in some cases cranial bones in the skull increase in thickness due to raised pressure in the skull due to the redistribution of blood and fluid in a headward direction.

The changes seen in the musculo-skeletal system of astronauts over time in microgravity are often similar to changes seen on earth. For instance patients who are immobilized and may have to spend large amounts of time in bed lose muscle and bone mass in a similar way to astronauts. Osteoporosis is a pathology commonly seen in post-menopausal women on earth, which causes the bone to become weak and brittle; symptoms very similar to osteoporosis are often seen in astronauts returning after time in space. These are just two examples of microgravity induced changes mimicking terrestrial problems, however there are many more and this link between space and terrestrial medicine is what makes microgravity such a valuable tool in our ability to understand and combat common terrestrial pathologies. In time research into the space equivalents of many terrestrial illnesses will enable us to gain a far greater understanding of their mechanisms and eventually help scientists develop better treatment and rehabilitation programs.

The microgravity of space is a unique environment that cannot be consistently reproduced on earth for longer than about half a minute; and the advantages that can be gained from research in space are potentially huge. All the physiological changes to bone and muscle seen in space happen far quicker than they would on earth. Therefore studies that would take years on earth could in theory take weeks or moths in space; this combined with the fact that pathologies such as osteoporosis can be induced in space but not on earth mean that more accurately controlled trials can be achieved over a wider variety of subjects; in effect we can choose groups to study muscle and bone wastage in rather than make do with the people who already have this problem. An additional and possibly more exciting benefit is the fact that space represents a whole new environment, one which we are not evolved to live in; this means that understanding how space affects the human body has the potential to lead to new discoveries in the field of physiology and medicine that would not be possible outside the microgravity environment.

In the next decade with the ongoing development of the International Space Station, researchers from around the world will have a platform from which to investigate how bone and muscle are affected by weightlessness. This will allow a greater understanding of our musculo-skeletal physiology which could lead to new treatments for terrestrial pathologies that could change the lives of people of people with currently untreatable musculo-skleletal disorders in a way that would never have been possible on earth.