Do you ever drive past and look at people running along and think “How do they make it look so easy? How come their not puffing and panting? How can they run for 2 hours and I can only run for 2 minutes? ” The key is oxygen!
When we are exercising our muscles require oxygen (delivered via the blood flow) to work. Therefore it’s our body’s ability to uptake and deliver oxygen to the muscles so we can continue exercising. A fitter person can extract oxygen from the blood much more efficiently than an unfit person. By undertaking an endurance training program your muscles develop a greater ability to uptake and deliver more oxygen therefore you can work for longer durations and at higher intensities.
There are two reasons which effect oxygen transport in the body and therefore affect your endurance performance. One reason for this limitation to endurance performance is the steps involved in the oxygen delivery from the air to the muscles and the other is the steps involved in the extraction and utilization of oxygen by the exercising muscles.
So the reason why those people you see running around the parks barely look like they are raising a sweat (and their breathing rate) is simply because they can use oxygen better! The key to improving oxygen uptake and delivery to your exercising muscles is endurance training and lots of it.