Contributor: Rich Butler, MS, USPTA
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Let’s settle this debate. If you were asked to select the most important muscle in your body, what comes to mind? The answer might depend on whether you are posing on your beach towel, firing away on the golf range, or tossing that kettlebell around. The ‘core’ would get some votes. Certainly your primary movers like the quads or the lats for the cross-country skier might receive some support. But the muscle I would choose is rarely seen yet, can produce the most profound outcomes. The work it does might be compared to the ant dragging the French fry. It was the organ (hint) that got much of the attention at the Harvard Fatigue Lab back in the early 1900s. It is also, ironically enough, one of the most neglected in the industrialized nations of the world. The answer is cardiac muscle, specifically the left ventricle. It has arguably more to say in your short-term and long-term health than any other muscle in your body.
Pumping blood seems easy enough, especially given that we only move with any conviction for ~5% of the 1440 minutes in our day. And while we are at rest our systolic blood pressure barely pushes back at 110 mmHg. Yet, when we loosen the reins, so to speak, on the tennis court, power walking up a hill, or getting down to Earth, Wind and Fire, the dynamics of delivering blood change considerably. One way to relate it would be to ask you to fill up those long thin balloons for the upcoming party. My mother would try and stretch them out to loosen them up first so they were more compliant. That is the role of nitric oxide, your arteries relaxing and growing larger (vasodilation) at the start of exercise. The effort you must give to blow up a balloon is the type of effort your left ventricle has to give 120 to 180 times a minute for as long as you are participating in your activity. It has to push hundreds of thousands of red blood cells full of oxygen down through arteries, arterioles, and then capillaries, single cell-wide capillaries, into the calf, the quad, the glute, and the hamstring as you finish your interval, turn the corner for home or crank out high watts on the rower. With arterial pressures continuing to mount and skeletal muscle calling for more oxygen with each contraction, the demands on the heart rise. The good news is you have just the tool for the job, the left ventricle.
The left ventricle contains approximately 3x the mass of the right ventricle. Measuring the stroke volume (volume of blood pumped from the left ventricle per beat) of the left ventricle can be difficult, but a VO2 max (the measurement of the maximum amount of oxygen that an individual can utilize during intense or maximal exertion) test lends some great insight regarding heart function. It is the cardiovascular system that has the overall vote on an individual’s VO2 max in most cases. First of all, the peak absolute VO2 max (ml/min) is measured. Then, if that number is divided by the highest heart rate achieved you have a value called oxygen pulse or the amount of oxygen used per beat of the heart. Oxygen pulse is associated with stroke volume or the proficiency of the left ventricle. For females a score > 9 ml O2/beat is predicted and for males a score >16 ml O2/beat. A recent test we completed for a 40 year old male showed a VO2 max of 2400 ml/min which was divided by a max heart rate of 170 bpm for an oxygen pulse of 14.1 ml O2/beat (below expected). This score does not meet the normal values for males, so some further investigation is necessary.
One other example is of a 57 year old female with a history of running, but for the past few years she has been irregular with her aerobic training and gained 30 lbs. Measuring VO2 in this case also helps with answering the question if her fitness level is independent of the weight she has gained. She peaked at 1780 ml O2 with a peak heart rate of 163 bpm.
Once in a job interview I was asked if I knew anything about a new style of exercise that was very trendy and ‘hot.’ It turns out I knew very little about it, and I still don’t. Although not revolutionary, ‘cardio’ training is unmistakably one of the most productive mechanisms to enhance yourself physically. For most of us, skeletal muscle can clean up the mess of a 2 year sabbatical or 2 weeks on a cruise, but it can’t do it alone. You need to be able to deliver the life blood (I believe that phrase is most appropriate in this context) of oxygen and clean up all the waste product of normal fat and sugar metabolism, which is where your left ventricle comes in. Although it is not February, I treat every month like heart month and continue to promote activities that lead to improvements in the cardiovascular system. So, how about lacing up the sneakers and getting after it?
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