When you read about people dying of “natural causes,” it usually means that they died of heart failure because they spent too much time lying in bed. When you become inactive, you lose your skeletal muscles at an alarming rate, and losing skeletal muscle causes loss of heart muscle until your heart can become too weak to pump blood to your brain and you die.
In 1914, Dr. Ernest Starling described what is today known as Starling’s Law, that strengthening skeletal muscles strengthens heart muscle and not the other way around (Circulation, 2002;106(23):2986-2992). When you contract your skeletal muscles, they squeeze the veins near them to pump extra blood back to your heart. The extra blood flowing back to your heart fills up your heart, which stretches your heart muscle, causing the heart muscle to contract with greater force and pump more blood back your body. This explains why your heart beats faster and harder to pump more blood when you exercise. The harder your heart muscle has to contract regularly in an exercise program, the greater the gain in heart muscle strength….