Just as you'd expect, the only way to keep your heart strong through exercise...
Is to push it to its limits on a regular basis.
However the problem with almost all forms of exercise...
Including the gym, and many field sports is...
While they do require the heart to work much harder than at rest...
They rarely, if ever, require it to beat at its absolute maximum level.
Sprinting however, is one of the only exercises there is...
Which requires you to be at or near your maximum heart rate with every single attempt.
And by maxing out your heart rate this regularly...
Not only do you keep your max heart rate higher...
You keep your resting heart rate lower as well.
These two numbers compared are known commonly as...