If the Heart is a Muscle, Why Doesn't it Tire?
If we keep using the same muscle(s) continuously for extended periods, those muscles get tired. Why then doesn’t the heart ever get tired? After all, it is a group of muscles too. And it beats (and need to beat) continuously over the entire life of the individual. What’s the difference? The answer lies in physiology. Most muscles like the bicep work via anaerobic metabolism, i.e., metabolism without oxygen. They burn glucose without oxygen, produce energy and also lactic acid. It is the buildup of that lactic acid that causes us to feel fatigue in those areas. The heart, on the other hand, does aerobic metabolism, i.e., metabolism with oxygen. The efficiency increase in energy production is 19 times! Wait, there’s more. Cardiac muscles have a “refractory period”. Skeletal muscles can be simulated to contract and expand rapidly. That is good, in fact necessary, for many situations like quick acceleration and rapid actions. Cardiac muscles, on the other...