Answer:
When we inspire, we are introducing different gases into our lungs, including oxygen.
When the inspired air reaches the pulmonary alveoli, oxygen passes into the blood and through hemoglobin is transported by the arteries to the muscle cells.
Muscles take oxygen and return carbon dioxide (one of the waste products of exercise) to the blood, which through the veins takes it to the heart.
The heart receives this blood with carbon dioxide and sends it to the lungs; there, the pulmonary alveoli absorb and produce the expiration of the lungs by means of which it eliminates carbon dioxide.
This joint work between the respiratory and circulatory system is produced by performing approximately 17 breaths and 70 beats (both per minute) in a normal adult, approximately, of sex, age, height and weight.
As we exercise the body (for example, a jog, a run of approximately 12 minutes or maximum speed tests), the cells of our muscles spend more oxygen than at rest, therefore, our lungs, which inspire faster to contribute more oxygen to the blood and the heart must also beat faster to send that oxygen quickly to the muscles.
In work done in the Physical Education classes, I have found that after an important physical work, the heart rate in the students has reached 180 beats per minute and the respiratory rate up to 40 times at the same time.
After an active rest (walking), of approximately 3 minutes, in the classes it was verified how the heart and respiratory frequencies decrease, since the cells of our muscles are no longer working intensely and therefore they are not consuming so much oxygen.
Continuing the active rest for 3 more minutes, the heart and respiratory frequencies continued to decrease and in some cases returned to normal.
