What effect does microgravity have on the human skeletal system and muscles?
Several studies have been done to assess the effects of microgravity on the human body with the goal of preventing muscle atrophy and a decrease in bone density that is common among astronauts. In space, bone density tends to decrease as the bone mineral turn-over rate decreases, and this results in a greater chance for broken bones upon return to Earth. Similarly, muscles undergo weakening in a microgravity environment. Muscles consist of one-celled fibers of various lengths that may be of two types: slow-twitch or fast-twitch. The slow-twitch fibers are responsible for continuous movement, total body support, and resistance to gravity. The fast-twitch fibers produce the force needed during rigorous or intense activity. In a microgravity environment, the leg and back muscles, which are used to resisting gravity, no longer have to provide support, and consequently the fibers become smaller, or atrophied. This decrease in muscle mass poses a major problem upon return to the 1G environme
