Dan jumps rope once a week at 65%-85% of his maximum heart rate for 20 minutes. If Dan wants to improve his cardiorespiratory endurance, he will need to increase:

The answer is to increase the minutes in which he is doing the exercise. He can just increase it by a couple of minutes and he will gradually improve his endurance.

People who utilizes the progression principle will ensure their exercise program increases in frequency, intensity, time, and type. the changes need to happen gradually in order to ensure they make gains in their fitness program. a person who doesn't utilize the progression principle can still gain health benefits from exercising, but will not continue to improve in cardiovascular fitness.

Target heart rate is the answer