True or False. Measuring heart rate allows the exerciser to determine if they are working too hard or not hard enough?

 True

Explanation:  Your heart rate measures the speed of your heart (beats per minute).  This helps measure the body's physical fitness rate.  If your physical activity increases or you are working harder to do something, then your heart rate goes up.  If your physical activity decreases or working not as hard, then your heart rate goes down.  Your heart rate can also depend on your diet and stress.  

i say that the answer is 'd'

you! go to the gym or i will kick you out of here to the gym