Heart Rate and Wellness: The Truth

by Mike DePrekel

Many people have said to me over the years something like “This exercise is good. It really gets my heart rate up.” While the exercise may indeed be “very good”, when and how to use your heart rate in regards to exercise intensity or stress is a topic that many individuals do not accurately understand.

Let’s take a look at the heart first. Is the purpose of exercise really to get your heart rate up? In order to answer this question, we need to find out exactly what the heart’s job is during exercise and what the heart has to do to meet the demands of our bodies during exercise. We all know that the heart is a muscle that pumps blood to the entire body. When our heart does more work by pumping stronger, faster, or both, it needs more energy, just like any other muscle. Like your skeletal muscles, your heart relies on oxygen (O2) to combine with food energy to make usable energy. The heart’s blood supply is the coronary arteries, where O2 is delivered to the heart muscle itself and waste is removed. The coronary arteries get bigger in a process called vasodilation in order to supply the heart with an increased amount of O2 to meet the demands of exercise and the increased work the heart must endure during exercise. On the other hand, the heart’s contribution to your body’s increased demand during exercise for O2 is met by pumping faster.

The heart is a gauge that reflects how hard we are working during exercise. We use our heart rate to assess how much O2 we are using during exercise. We have all heard of the term “aerobic.” That term actually means, “using oxygen”, which is important to know because it is only appropriate and valid to monitor our heart rate during aerobic exercise. During aerobic exercise our heart rate has a linear association with how much O2 our body is using. As our O2 usage increases, our heart rate follows the same rate increase, which explains why we can monitor our exercise intensity via our heart rate when we exercise aerobically. The measurement of aerobic fitness is how much O2 our bodies can use aerobically. This can be translated into a fitness number, commonly referred to in exercise science as VO2, (in every day terms, this is the volume of O2 our body can use aerobically). It is usually measured as the rate of O2 used or consumed per kilogram of body weight per minute of time. It is reported that Lance Armstrong’s VO2 score is in the high 90s. A thoroughbred racehorse might have a VO2 of 135!

So the comment of “this exercise is good, it really gets my heart rate up” may indicate that you are performing aerobic exercise, and are monitoring your heart rate to gauge your intensity. But many things actually can elevate your heart rate, including anger, fear, or even weight training. Your heart rate might even be in your target heart rate zone. However, weight training is not aerobic. It is anaerobic, meaning “taking place in the absence of O2.” During anaerobic exercise, the association of heart rate to O2 usage is no longer linear. In fact, there is little correlation between your heart rate and exercise stress. Your heart rate during weight training or other anaerobic exercises is an erroneous measure and should not be used to indicate exercise stress. During weight training, the heart beats faster due to a pressure response. Simply put, as the intra-thoracic pressure greatly increases during weight training, the heart needs to relieve that pressure by beating faster. In other words, if 150 ml of blood comes into the heart with great force, then 150 ml must come out. So the heart beats faster during weight training due to a pressure response and not as a need to supply the body with increased O2.

The implications of this misuse of heart rate monitoring can be great. In the United States, heart disease is the number one killer in both men and women. High blood pressure is a major or primary contributor to heart disease. Here are two case examples that illustrate this concern.

Bob is a husky 35 year old. He has always been a big man, a little heavier on body fat but he has a very large girth, is large boned and has large muscles. Bob does not run very well, but he is strong. Bob played high school football, but is now out of shape, as he does not engage in regular aerobic exercise. His recent trip to the doctor revealed Bob has high blood pressure, and his doctor has strongly suggested he become more active and start exercising to control his hypertension. Bob is concerned for his health and joins a local health club. Since Bob is still very strong and he never was good at aerobic exercise and thus never really liked it, he naturally goes right for the weights. Bob lifts weights hard. He often holds his breath briefly (something he should not do) as he lifts very heavy weights. After 3 months, Bob feels a lot better about himself and feels stronger. He is looking forward to his upcoming visit to his doctor and is sure that the exercise he’s gotten is helping his high blood pressure. At the doctor’s office, Bob is dismayed that his blood pressure has actually increased slightly. How could this be? Bob has done what the doctor has told him to do!

Another woman named Mary at the gym has high blood pressure as well. She has recently joined a group class with many other ladies that involves weight training at a rapid pace with little rest in between exercises. Her heart rate is swift during these routines and reaches her age-predicted target heart rate zone. She goes to the gym three days a week and the class is the extent of her exercise program. At the doctor’s office, she, too, is dismayed by her results. Her blood pressure did not significantly change.

The reason Bob and Mary were not able to lower their blood pressures is that they have only relied on resistance training or anaerobic exercise to reduce their blood pressures. Exercise physiologists know that the adaptations to aerobic exercise and resistance training are quite different. The trick is to be able to identify when we are performing aerobic exercise. Bob and Mary would be more successful in reducing blood pressure by engaging in more aerobic exercise, such as walking, biking, swimming, etc. According to the American College of Sports Medicine (ACSM), aerobic exercise should be rhythmic in nature and last at least five minutes using large muscles. Weight training is an anaerobic form of exercise that requires one to only be able to endure movement for usually 20 seconds or so before needing to take a rest. Even with the group class that Mary took, she had to take brief rest periods or switch muscles every 30 seconds in order to continue with the 45-minute class. As a result, using the heart rate as an indicator of exercise stress or wellness is not appropriate.

How high should your heart rate be when you exercise aerobically? There are two methods that are used in the field. For both methods, you will begin by subtracting your age from 220. The most popular method is to then take that number and multiply it by 70 to 85%. Another method is called the karvonen formula. It uses your resting heart rate as a measure in order to be more accurate. Take the number you got from subtracting your age from 220, then subtract the product of your resting heart rate times 60 to 80%, and then add back your resting heart rate. You can use your target heart rate to not only tell you if you are exercising most efficiently for your health and fitness status, but also as a gauge to let you know when you need to ease up on the amount of exercise you are performing. Exercise your right to good health!