The answer to this is; the fuel we consume (food) is converted into energy to power body function. We are basically a fuel cell producing energy; the resulting by-products are CO2 and of course body waste.
It is important to exercise our joints and muscles generally but, specifically our lungs and chest, they are interdependent, as we move around through the course of the day we are building up our aerobic strength, strengthening both lung function and muscle tone. Our connective tissue also becomes healthier and suppler and less prone to injury both from tearing and straining. — Read Article