"During the fast you lose muscle protein and you need to replenish it with exercise. Does anyone here exercise after the fast? When do you start exercising? What kind of exercising do you do? Do you Join the gym or do it at home?"
Muscle protein is not replenished by exercise after a water only fast, but by the protein (or more specifically, the amino acids) that you eat as part of the diet post-fast, and where exercise needs to be introduced on a gradual basis and within the capabilities of your body in doing so.
Your food reserves will need to be replenished as a priority and therefore the re-feeding period should only involve a minimal amount of activity. However. once these food reserves are replaced towards the end of this period, gradually build-up your exercise programme to achieve higher levels of fitness and bodily strength.
One of the most efficient exercises (according to NASA) is "rebounding", which is reported to be 68% more efficient than jogging, and the only "cellular" exercise in existence.
BODY PROTEIN DURING THE FAST.........
The body needs a tiny amount of glucose for some functions on a water only fast, so a very small amount of protein (18-24 grams), is catabolized (a process by which complex substances are converted by living cells into more simple compounds, with a consequent release of energy) to supply it --- from 1/2 to 1 ounce of muscle tissue per day.
Over a 30 day Water Fast a person generally loses a maximum of 1-2 pounds of muscle mass. The body conserves its protein as an evolutionary development, and that exists to protect muscle tissue and vital organs from damage during periods of insufficient food availability.