Investigate methods for measuring muscle and bone mass changes in astronauts and animals which occur during space flight

Sodium-22 is being used as a tracer for bone mineral metabolism studies. Dogs are being grown from puppies to adulthood on a diet containing a constant level of sodium-22 in order to uniformly tag the entire skeleton with a long lived radionuclide. This study is still in progress and the dogs are still growing. Potassium-40 measurements were made on people, who are replacing muscle mass lost due to leg injuries, in a second study. It appears that potassium-40 measurements provide an accurate and convenient method for determining relative changes in the muscle content of the leg.