The heart is a muscle. The more you exercise it, the stronger it becomes. With this in mind, contrast the resting heart rate of an athlete with that of an inactive person.

The heart of a lazy person pumps blood less efficiently than an athlete who has trained and prepared to achieve a high performance, this can be understood with the example of football players who will play in other countries that have a higher altitude than the country of origin and has to go before to get used to the rarer air

Cells of an organism tell each other when predators are near.