AREAS OF INTEREST: FAST TWITCH, SLOW TWITCH, FAT THEORIES, FAT CELLS. by: Tom Seabourne Ph. D The number of muscle fibers and type (fast twitch or slow twitch) in your body was determined during the 2nd trimester of your mother's pregnancy. Each of your muscle fibers is composed of 75 percent water, 20 percent protein, 5 percent phosphates, calcium, magnesium, … [Read more...] about YOU CANNOT CHANGE YOUR MUSCLE FIBER TYPE, SO YOU SHOULD PRAY FOR GOOD GENETICS