The answer, of course, lies in the principle of special relativity.

According to Einstein, we are all constantly moving at the speed of light through the four dimensions of spacetime.

Now, as you and I are sitting on our respective asses scarfing potato chips and staring at the phosphorescent glow, we are not moving relative to each other. Our relative stasis means that the entirety of our spacetime vectors are directed into the time dimension. Maybe that sensation you feel isn't your bum falling asleep, but the rush from your lightspeed plunge through time.

A person who is jogging, however, is in motion through space. In other words, she has a space component as well as a time component in her spacetime vector. Since a portion of her lightspeed motion through spacetime is diverted towards her movement in space, she is moving more slowly through time than us fatasses. It follows that, because our greasy crumb-covered bodies are moving more quickly through time, we will age at a faster rate.

Thus people who jog on a regular basis actually experience less time than us lazy stationary cake eaters, and on average will live longer relative to us. QED.