Ever wonder about your heart? As cyclists we don't tend to worry much about heart disease or the other tangential problems associated with sedentary life styles, we pay attention to heart rate (maybe a little too much sometimes) but we don't often think about the heart itself, and what it is doing.

Your heart is the most naturally gifted endurance muscle in your body. It is a fist sized (approximately) muscle that contains four separate chambers that control the flow of blood to the rest of your entire body. It accomplishes this task by contracting with great force and ejecting the blood through arterial vessels that lead to all the other blood vessels of you body. That becomes incredibly impressive when you realize that there are somewhere near 60,000 miles of blood vessels in your body (that's not a typo). Of course your body has a few other tricks that aid the heart in this daunting task, and not all these blood vessels are profuse at the same time. But your tissues are demanding little whiners, and your heart is a slave to their demands.

The average person has approximately 5 liters of blood in their body at any given time and the average resting heart rate is approximately 72 bpm (doesn't that seem high?), the average amount of blood pumped by each beat of the heart (called stroke volume) is approximately 70 ml per beat. Doing the highly complex math (70mL/bts * 72bts/min) gives us 5040mL/min; approximately your entire blood volume cruising past your heart every single minute. Okay, why is that at all relevant? Because everything you do on the bike depends ultimately on your heart being able to deliver blood to those thundering quadriceps without shutting off the supply to your brain (though I'm pretty sure that sometimes happens).

So how is your highly trained cyclist heart different from the "average" heart? It's called "Athletic Heart Syndrome"; The constellation of normal anatomic and physiologic adaptations in persons who regularly perform strenuous dynamic exercise . In the endurance-trained athlete, dilation of all four cardiac chambers and increased left ventricular wall thickness increase the pumping capability of the heart. This syndrome, which would be considered abnormal in an untrained person, is a successful adaptation to endurance exercise. Cool, huh? In fact studies have shown that heart muscle mass in the left ventricle of untrained subjects increased by 30% after only two weeks of training. Of course the unfortunate corollary is also true, trained runners lost nearly 30% of their left ventricular muscle mass two weeks after they stopped running.

Okay, so the pumping capacity of the heart (stroke volume) both increase and decrease dramatically in a short period of time, depending on activity levels. Since overall cardiac output is a function of stroke volume times heart rate it makes sense that as stroke volume increases you can do the same amount of work at a lower heart rate. Basically, the more work you can do at a given heart rate, the fitter you are. But stroke volume can only increase so much, beyond which no amount of training will budge it. Increased stroke volume appears to be the primary factor behind the initial performance gains made when a person begins a training program.

What does all this mean to you? Adaptations of the heart are somewhat ephemeral, which means that rest weeks and tapering for big events can produce declines in these important adaptations. There is some evidence that by sufficiently decreasing volume of training, while maintaining some intensity work, one can benefit from rest without sacrificing much in terms of heart fitness (remember, a small amount of hard goes a long way.). The other important implication of the heart's "what have you done for me lately?" attitude is that in order to maintain a strong heart over the course of your life, you must maintain an active lifestyle FOR YOUR ENTIRE LIFE. Ray H. always says after a good King Ridge ride "Well, we've got that one in the bank." And while that may be true physiologically in terms of many other adaptations, it will only satisfy your heart for a little while.

-Erika Floric