What factors affect the yield and composition of meat after cooking?

http://www.all-science-fair-projects.com/project488_39.html

. Procedure

1. Shape 120 grams of ground beef into a round patty 1.0 cm. thick. (This is a rather thin patty.)
2. Cover part of a broiler pan with aluminum foil and poke holes in the foil to let the fat drip through.
3. Turn on the broiler in the oven and place the broiler pan in the oven so the top of the meat is about 9 cm. from the coil. (This will probably be the second rack slot down.) Leave the door of the oven part way open.
4. Cook the patty until either medium or well-done.

   	Medium-done - broil until the center of the patty is a pinkish-brown color (about 10 min. - 5 min. on each side.)
   	Well-done - broil until the center of the patty has no evidence of pink (about 16 min. - 8 min. on each side)

5. Weigh the cooked patty immediately after cooking, place on a plate and cut in half.
6. Calculate yield percent as follows: (cooked weight/starting weight) x 100
7. Report yield and observe color and firmness. Tasting is not necessary and not advisable for the medium-done patties.