Answer: You know that an activity is building cardiorespiratory fitness when you can perform exercises at an optimum level of intensity or degrees over a long period of time with an increased consumption of oxygen by the body.
In other words, cardiorespiratory fitness is said to be built when one can engage in physical exercise over a long period of time without getting tired, exhausted or experiencing breathlessness.
Explanation: When the muscles of the body especially the skeletal muscles are being supplied with oxygen by the circulatory and respiratory system during a sustained or prolonged physical exercise, cardiorespiratory fitness is said to be achieved.
Cardiorespiratory fitness is otherwise known as aerobic fitness.
