How do the cells in your body get energy?

Cells get energy from the chemicals in food. Cells also produce ATP for energy used in cellular processes, such as cellular respiration. I hope I helped! :)

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)

No, when getting the flu vaccine no drugs should be being takin at the time.