Question

MEASURES EXERCISE INTENSITY

Answer 1

use your target heart rate

Step-by-step explanation:

The human body has an inbuilt system to measure its exercise intensity which is the heart.

Answer 2

There are two basic ways to measure exercise intensity:
How you feel. Exercise intensity is a subjective measure of how hard physical activity feels to you while you're doing it — your perceived exertion. ...
Your heart rate. Your heart rate offers a more objective look at exercise intensity.