Cardiovascular exercise frequently referred to as "cardio" or "aerobics" creates a continuous durational challenge on the heart. Usually done without rest. This mimics prolonged stress in a native environment. The heart feels like its under constant threat and attack. "Cardio" exercise is a waste of time and effort. The birth of long distance running, began with the ancient Greek long-distance messenger, Phidippides. He ran 26.2 miles from Marathon to Athens to tell of the victory of the Greeks over invading Persians. On his arrival, all he could master from the long distance he had run was "Nike!" (meaning Victory) then collapsed and checked out (died).
Forcing the body to perform the same continuous cardiovascular challenge, by repeating the same movement, at the same rate, thousands of times over without variation and without rest is unnatural. When looked at from an evolutionary perspective, this type of demand could have rarely happened. The problem has been the belief that the aerobic metabolic pathway can be isolated from the rest of metabolism. Metabolism is an uninterrupted whole that is intrinsically tied together. The aerobic machinery is fueled by the substrate pyruvate, which can be produced only through anaerobic pathway. Forced, continuous, endurance exercises induces your heart and lungs to "downsize" because smaller allows you to go further more efficiently with less rest and less fuel. What's with increasing durational capacity through downsizing? Instead of building heart strength, it robs it of vital reserve capacity. Heart attacks don't occur because of a lack of endurance. They occur when there is a sudden increase in cardiac demand that exceeds your heat's capacity. Giving up your heart's reserve capacity to adapt to unnatural bouts of continuous prolonged duration only increases your risk of sudden cardiac death.
Understand that your aerobic system performs at its highest level when recovering from lactic acidosis. After high-intensity workout, when your metabolism is attempting to reduce the level of pyruvate in the system, it does so through the aerobic sub-segment of metabolism. Muscle is the basic mechanical system being served by the aerobic system. As muscle strength improves, the necessary support systems(which includes aerobic system) must follow suit.
