That's an unfortunate fact of life. None of us is going to look like Arnold Schwartznegger unless we exercise like him. Weightless life in space is more akin to time spent as a couch potato. When astronauts return and reload muscles B particularly with activities, such as walking down stairs or down a hill, that simultaneously stretch and contract muscles, the result is microscopic tears in the membrane of the muscle cells. Excessive cell tearing also is a factor in the progressive, debilitating disease Duchenne's muscular dystrophy, he said.
B rushes in to promote healing or wreak destruction.
Inside muscle cells, the normal, low levels of calcium signal muscle contraction. In studies first done in sea urchins and fibroblasts, Dr. McNeil documented that when extracellular calcium rushes in through a tear in the cell membrane, it can either help form the cell-saving patch or destroy the cell, possibly by prompting the cell to contract to death. There is complete restoration of the surface covering of the egg within seconds. The cell-saving patch results from a fusion of vesicles, little spherical structures that normally nourish the cell, and the initial onslaught of external calcium. The patch then fuses with the cell surface.