Chronic adaptations to aerobic exercise

     Generally speaking, as you train aerobically your body reacts in two different ways: acute and chronic. Acute being short term adaptations and chronic being long term adaptations. Acute responses happen in your heart, your lungs and your muscles. Acute responses generally involve more blood circulated throughout the body and in return the expenditure of carbon dioxide, more oxygen pumped throughout the body and more turnover with muscles involved within the exercise. More long-term adaptations involve these processes becoming better and more efficient. As long-term training occurs your body becomes more adapt at breathing patterns pertaining towards the event. Running breathing patterns differ from swimming breathing rhythm. The more you conduct a specific activity the better your body becomes at those specific breathing patterns. Your cardiac output (amount of blood pumped per min) will improve, increased stroke volume (how much blood is pumped per beat), and a lower resting heart rate (body becomes more efficient pumping blood thus the lower heart rate). More blood means more myoglobin which means more oxygen. For full disclosure when I say long term adaptations, I mean consistent running for a range of 6-12 months. If you can remember back to resistance training neural adaptions occur first. Same with aerobic training. For aerobic training the body needs to be in a constant state of activation, so the firing of motor units is more offset providing the body with consistent movement. To put it in perspective it is like going to the gym with an extremely light bench press and performing an extreme number of repetitions. In that scenario you want those chest muscles to continuously fire into to lift the weight. Same principle applies towards aerobic training. The brain signals that power motor units will fire in such a way to enable continued power towards the muscles. Metabolically, as you train aerobically the body becomes more adaptive to utilizing fat as a fuel source instead of carbohydrates. This allows the body to perform at prolonged activities at the same intensity.

    Muscular wise muscular fibers become more adaptive by increasing the number of capillaries within the muscle to respond to the increased need for oxygen. Additionally, the size and number of mitochondria's increase due to the increased energy requirement. As you can imagine with the increased number of capillaries and mitochondria the muscle fiber does experience some hypertrophy. Key word is some as type 1's do not experience the same hypertrophy as type 2 muscle fibers. Even when the aerobic effort involves predominately type 2 muscle fibers in events such as the 400m-800m sprint (I say sprint loosely has these are events that are brutal) type 2's do not experience the same hypertrophy as anaerobic training would. As long-term adaptations occur reduction in the concentration of glycolytic enzymes can reduce the overall muscle mass of those fibers. Ever see a jacked marathoner? That's why. The main adaptation is the increased oxidative capabilities of the muscle fibers. Type 1's are already have high oxidative properties; type 2's undergo transitions from type 11x to type 11a.