AstroFit.

WILLIAM J. EVANS AND GERALD SECOR COUZENS Because everything is weightless in space, astronauts' muscles shrink by about 2 percent to 3 percent per week and calcium is leached from their bones at an accelerated pace. The combined effect, weakness and loss of mobility, mimics what happens during the aging process here on Earth, especially for sedentary people. The process hampers astronauts' activities in space and makes it hard to recover on Earth. As head of the Nutrition, Physical Fitness, and Rapid Rehabilitation Team of the National Space Biomedical Research Institution, Evans has developed a program called AstroFit to prevent these problems in astronauts. It could also help keep any body strong. This guide outlines the 90-day program of exercises for building muscle mass and enhancing balance and prescribes a diet that's protein-rich and controls blood sugar. Evans' E-Centrics weight-training exercises are different from most, in that he focuses on the motion of lowering weights after a lift. Whereas most people who use weights lift them slowly and lower them quickly, Evans advises the opposite. Astrofit may be designed for astronauts traveling to Mars, but Evans asserts that it's good for everyone, especially people over 50 who are trying to restore bone and muscle mass. Free Pr, 2002, 307 p., b&w illus., hardcover, $24.00.