The heart is a muscle, and can be trained just like any other muscle in your body. Cardiovascular mechanisms and the inability to supply blood and nutrients to the different tissues in the body remain at the heart of many of the proposed models of fatigue, so this seems a good place to start our exploration…Cardio BasicsWe started a few weeks back with a general summary of the many models for how the body fatigues with exercise, and the most obvious for endurance athletes is the limits imposed by getting blood (i.e., oxygen and nutrients) to the muscles. Indeed, most of the other models are indirect spinoffs of cardiovascular limits.One of the things I really focus on with my exercise physiology class is the incredible efficiency of the body. With respect to the cardiovascular system, the resting cardiac output (amount of blood pumped through the heart each minute) is approximately 5 L. Thats also the rough amount of total blood in your body. So at rest, we can make the broad generalization that every red blood cell does one full circuit of your body in one minute.But with maximal exercise, the body has an incredible reserve capacity, such that highly trained individuals might have cardiac outputs of 30-40 L/min. So that means that same single red blood cell does a full circuit of your body every 7-10 s! All of this is achieved by a pump that is about the size of your fist, and the even more beautiful thing...
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