By Ryan Unverzagt

Welcome back to another edition of “From the Trainer”! I hope you enjoyed last month’s article about the amazing heart. We’ll continue the heart theme this month, too. I have discussed exercise heart rates in previous columns, but I’ll dive a little deeper into the methods on how to calculate these values. If you love to crunch the numbers, this article is right up your alley.

American Heart Association Target (AHA) Heart Rate Guidelines

The AHA recommends getting at least 150 minutes of moderately-intense exercise per week. This equates to at least 30 minutes a day, 5 days per week, or any combination that adds up to 150. But what is considered moderately-intense? The answer may surprise you. It’s not as difficult as you might think.

50-70% of your age-predicted heart rate maximum is considered moderate intensity. The age-predicted HR max is figured by taking 220-YOUR AGE. This is a very simple method. Example for a 50 year old:

220-50 =170 beats per minute (bpm)

50%–170 x 0.5 = 85 bpm

70%– 170 x 0.7 = 119 bpm

Considering that a normal resting heart rate is between 60-100 bpm, these numbers may not fit your recommendations by the AHA. In the example above, lets say the 50 year old’s resting heart rate is already at 85 bpm. This person will be exercising at a greater intensity level (70% or higher), especially if he or she is a beginner. Higher heart rates will be common at a low fitness level. Over time, the muscles and heart adapt to the fuel and oxygen demands of aerobic exercise. As a person gets in better shape, the resting heart rate will eventually decrease. Why does this happen? The heart’s stroke volume and cardiac output will increase, meaning that it can pump more blood per beat to meet the body’s demands. The heart becomes more efficient at filling up and squeezing. This will lead to a lower resting heart rate.

Another method to calculate exercise intensity is the Heart Rate Reserve or Karvonen Method. The heart rate reserve is the difference between your maximum exercise heart rate and resting heart rate. In the previous example, HR max is 220- AGE, however, this method can be off by 10 to 20 beats. According to the Cleveland Clinic website, researchers have come up with a different way to calculate maximum HR. Take your age and multiply it by 0.7 and then subtract this total from 207.

50yrs x 0.7 = 35

207-35 = 172 bpm (Max HR)

So far, not much difference in the age-predicted max HR from above (170 bpm). But, when you factor in your resting HR, the numbers can change dramatically. Measuring resting HR is easy. Most people have a smart watch that keeps track of the HR every minute of the day. Just sit quiet for 5 minutes, and then look at your watch. For those that don’t have one (like me), you can feel for a pulse using one of the carotid arteries on the front side the neck or on the thumb-side of your wrist for the radial artery. Watch a clock or start a timer on your phone for 30 seconds and count your pulses. Take that number and multiply it by 2. Say it’s 35. 35 x 2 = 70 bpm. So, for the 50 year old;

Heart rate reserve (HRR) = Max HR – resting HR

172 – 70 = 102 beats

Heart rate reserve is a good indicator of fitness level (the higher the number, the better). The more fit you are, the lower your resting heart rate will be, which means your HRR will be higher. So how can we use this method to calculate target heart rates? For moderate intensity, aim for about 50-70% of your heart rate reserve number. Once you have figured this, you will add your resting HR back in for your target HR numbers. Again, for the 50 year-old:

102 x 0.50 = 51

102 x 0.70 = 71

51+70 = 121 bpm @ 50% of HRR

71+70 = 141 bpm @ 70% of HRR

Take a look at these numbers compared to the original age-predicted HR max method. Big difference. 85-119 bpm vs. 121-141 bpm using the same percentages. It’s important to remember that both methods are estimates to figure maximum heart rate values. Unless you’re an elite athlete, it’s usually not safe, fun, or practical to have yourself tested to find out what your actual maximum heart rate really is. Surprisingly, I’ve seen multiple geriatric patients achieve well above their age-predicted max heart rates during treadmill stress testing in the cardiovascular lab.

You might be wondering which method is the best way to figure exercise heart rates. Even though the Age-predicted Max HR method is easier to calculate, the Karvonen method is a little more accurate. This factors in your resting heart rate, whereas the other one does not. And, as resting heart rates decrease, the heart rate reserve will increase, changing your target heart rate numbers. If the 50-year old’s resting heart rate decreases to 62 bpm, here’s how the numbers change:

172 (max HR)-62 (resting HR) = 110 beats vs. 102 beats

110 x 0.50 = 55

110 x .70 = 77

55+62 = 117 bpm @ 50% of HRR

77+62 = 139 bpm @ 70% of HRR

These target numbers change at the same percentages, but you’ll be aiming for the higher end of the range once you have some regular exercise under your belt. Remember, these examples are for moderately-intense exercise designed for cardiovascular health. If you are not sure if exercising is safe for you, especially if you have a heart condition, I recommend visiting with your doctor to discuss what’s best for your situation. The majority of heart medications will affect the heart rate (usually lower) and these target numbers may not align with your goals. Same goes for anybody with a pacemaker and/or defibrillator.

Apple and android smart watches calculate target heart rates using the 220-AGE method, which is perfectly fine. Some smart watches can also monitor oxygen and give ECG readings. What’s important here is that you stay active enough to produce positive changes for your heart and overall health. It doesn’t take much to make a big difference.

About the Author: Unverzagt holds a Bachelor of Science degree in Wellness Management from Black Hills State University. He is a certified Strength & Conditioning Specialist through the National Strength & Conditioning Association and a Registered Diagnostic Cardiac Sonographer through the American Registry for Diagnostic Medical Sonography.