The heart is a muscle which becomes more efficient with exercise. When you exercise, your muscles help to circulate blood through the body taking some of the strain and effort off the heart. Not as much work is needed to pump blood and the heart becomes stronger over a period of time

As you begin to exercise, your heart will contract faster and circulation will increase, which gets oxygenated blood to your muscles quicker. As the demand for blood increases, the heart is going to try to meet the demand by increasing the heart rate and also by increasing the force at which it contracts. The increase in oxygen delivery is twofold: your heart will have more beats per minute, and a more forceful contraction each time it beats so it can pump a greater amount of blood throughout the body.

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