For some people, walking around the block wears them out. For others, running a 10k is energizing. Some can swim a mile; others can dog-paddle 25 meters.
The amount of oxygen you carry in your blood and the amountDara Torres, for example, carries in her blood is about the same. It's how we stay alive (and don't have to be very fit either). Yet, Dara, at the age of 41, made the US Olympic swim team - for the fifth time.
Physical exertion depends on oxygen delivery and the more you train, smartly, the better you get. Dara Torres' delivery of oxygen to her working muscles is like Federal Express: quick, efficient, dependable. If you dog-paddle 25 meters and have to quit, your delivery system is more like the Pony Express. If you want to get more out of your life, change the Pony Express to Federal Express, train (read more about Dara' traininghere).
Training is exercise but exercise is not necessarily training. Training is goal driven, specific, measurable, consistent. Exercise is physical activity.
See the difference? What's keeping you from training?