Will exercise make your heart strong and healthy? Simple observation and a medical textbook proves the answer is no.
I hear it all the time, "...but the heart is a muscle, you need cardio exercise to keep the heart muscle strong." True, the heart is a muscle, but it's a cardiac muscle, which is an involuntary muscle, meaning you have no willful control over its function. The autonomic nervous system controls the strength of the heart's contractions. A skeletal muscle, like those in your arms and legs, is a voluntary muscle that you willfully control when to relax and contract, and with how much force.
The average adult has a resting cardiac output of five liters of blood per minute. Depending on oxygen demand from minute to minute, and without additional nervous system stimulation, heart rate and strength of contraction can be automatically adjusted to provide a cardiac output of up to 15 liters of blood per minute. This is the normal physiological capacity of a "resting" heart; physical training is not required to gain this, you are born with this capability. Should the need arise for cardiac output beyond normal capacity, sympathetic nerves can increase the pumping ability of the heart to as high as 25 liters of blood per minute. Again, you are born with this capacity and it occurs automatically, and it is not due to physical training.
Based on this information it should be clear that the heart is a perfectly capable involuntary organ. Physical training cannot give the heart a capability that it already has. Therefore the claim that exercise is necessary for keeping the heart muscle strong is untrue.
The reason exercise is important is not because of the effect it has on the heart, but because of its effect on the skeletal muscles. The pumping action of the heart is dictated by the muscles' metabolic activity. Exercise increases muscle metabolism and causes blood vessels to dilate. These changes signal the heart to adjust its pumping activity.
Stronger muscles are more efficient; they extract oxygen and dispose of waste products more efficiently than weak muscles. The goal of exercise should be to make muscles as strong as they're designed to be for the purpose of placing less stress on the heart. Unfortunately mainstream exercise guidelines lead to muscle wasting which leads to unnecessary stress on the heart.
Will exercise make the heart healthier? There is actually no scientific evidence showing that exercise can make a heart healthier. I have personally witnessed patients participating in cardiac rehab programs have heart attacks again while following mainstream exercise guidelines.
In summary, the heart is an involuntary organ that cannot be made stronger or healthier by exercise. Strengthen your skeletal muscles and save your heart from undue stress.
Don Bennett's Comments:
There was an interesting study done where out of shape people were put on a workout program for their lower body -- stationary bicycle training -- but first their "cardio" fitness level was assessed. The test measures "VOMAX" -- a measurement of aerobic capacity -- and is done by raising the heart rate and measuring respiration and oxygen utilization. To do this, the participants pedaled a bicycle while hooked up to a machine. They underwent three tests, once with the right leg only, once with the left leg only, and once pedaling with both legs. As expected, all three test results were the same for each participant. Then the participants worked out on the bicycle for a 90 day period... but only with one leg! That's right, one leg pedaled while the other just hung out. At the end of the 90 day period it was visually obvious which leg had been trained and which one hadn't, but the real test was the VOMAX testing. When testing VOMAX with the leg that had been worked out, as expected VOMAX was much improved. But what do you think the VOMAX test result was when the leg that hadn't been exercised was used for the test? You guessed it, no increase! What does this mean? There is no such thing as a "general overall aerobic efficiency", ... aerobic efficiency is muscle specific! It is NOT dictated by the condition of the heart, or lungs, or blood or any other part of the cardio-pulmonary system. So what does this say about training which focuses on "target heart rate"?