Long distance runners and cyclists usually have a lower than average resting heart rate. Suggest why a low heart rate has developed in these people.

Long distance runners and cyclists often have a lower than average resting heart rate due to their high level of cardiovascular fitness. Here's a step-by-step explanation:

1. Regular Exercise: Long distance runners and cyclists engage in regular, intense exercise. This strengthens their cardiovascular system, including the heart.

2. Heart Efficiency: Over time, the heart becomes more efficient at pumping blood throughout the body. This means it can pump the same amount of blood with fewer beats, leading to a lower resting heart rate.

3. Oxygen Utilization: Regular endurance training also improves the body's ability to utilize oxygen, reducing the workload on the heart.

4. Adaptation: The body adapts to the demands placed on it. In the case of endurance athletes, the body adapts to regular, prolonged exercise by developing a more efficient cardiovascular system, including a lower resting heart rate.

5. Health Benefits: A lower resting heart rate is often associated with better cardiovascular health and fitness. It's a sign that the heart is working efficiently and doesn't have to work as hard to pump blood.

In conclusion, a lower resting heart rate in long distance runners and cyclists is a result of their regular, intense exercise which leads to improved heart efficiency and cardiovascular fitness.