The more you exercise and the harder you push yourself, the harder your body has to work. Your heart rate will increase to increase the flow of blood throughout your body. This keeps you functioning....
A theory is an idea that has not or can't be proven. Its an attempt to explain how something works, but it could be wrong.add some theorems are pretty definitive, such as Pythagoras's Theorem...
if electricity didn't exsist, neither would we. apparently atoms are jopined up by electrical field. if this is not true, we would simply be living off candles and writing letters instead of light...