Understanding Your Heart Rate

By Paula Poh

Hi Gals! Do you know if you’re working out at the right intensity? Do you know what your heart rate should be when you’re working out? Or how to keep track of it? Don’t worry if you don’t, because it’s easy to find out!

Before we begin, we need to know your resting heart rate (RHR). This is the number of times your heart beats per minute at rest. Various factors can affect your RHR, such as environmental temperature, emotions, posture, body size, being sick, medications, etc. A normal RHR can vary between 60 to 100 beats per minute. If you are more conditioned (i.e., working out regularly) your RHR will be lower, because your heart is more efficient at pumping blood throughout your body with each beat. Conversely, if you are less conditioned (i.e., not working out) you’ll tend to have a higher RHR.

Since RHR can fluctuate throughout the day, the best time to measure it is in the morning—waking up naturally (i.e., without an alarm) after a good night’s sleep and before getting out of bed. This may be difficult, but it’s possible! The best—and easiest—way to find your pulse is on your wrist alongside your thumb via the radial artery, or the neck via the carotid artery. Use your index and middle finger (not your thumb) to apply slight pressure to the artery of your choosing and count the number of beats for 60 seconds. This should be performed at least on three different days to get an average reading.

In addition to knowing your RHR, you should also know your maximum heart rate (MHR). To calculate your MHR, subtract your age from 220 (ex: if I’m 21 my MHR would be 220-21 = 199). Theoretically your MHR is the highest rate your heart can beat during exercise. This will decrease with age. While the “MRH = 220-age” formula provides a rough estimate, the most accurate way to determine your MHR is with a cardiac stress test or exercise tolerance test. But for the most part the formula is pretty spot on.

Now that you know your RHR and MHR, you can determine the target heart rate (THR) zone to determine the intensity of your workout. THR can range from 50% to 85% of your MHR and is reported as a range. Workouts toward the lower end (50%-70%) are considered moderate intensity and burn more fats. Alternatively, workouts on the higher end (70%-85%) are considered vigorous intensity. These burn more carbohydrates and improve cardiorespiratory fitness (e.g., better stamina/endurance). Although you are burning more carbs with vigorous intensity workouts, you are still burning fats, so don’t limit yourself to just moderate intensity workouts if your goal is to lose weight. There is much to gain from vigorous intensity workouts.

While there are several mathematical formulas to calculate THR zones, the Karvonen formula tends to be more accurate since it takes into account both RHR and MHR. Since you know both, all you have to do is plug and solve!

To solve for moderate intensity THR range (50%-70% of MHR)

THR=((((220-age)-RHR)*0.5)+RHR)

THR=((((220-age)-RHR)*0.7)+RHR)

To solve for vigorous intensity THR range (70-85% of MHR)

THR=((((220-age)-RHR)*0.7)+RHR)

THR=((((220-age)-RHR)*0.85)+RHR)

If you have a fitness tracker that monitors your heart rate, you can use it during your workout to make sure you are working within your THR range. If you don’t, you can manually measure your heart rate at your wrist or neck like you did for your resting heart rate.

Now, if doing all this math is just too much for you, there are other ways to gauge your exercise intensity, one of which is the Borg’s Rating of Perceived Exertion Scale, or RPE. This scale measures how hard you are working, and there’s no right or wrong answer, it’s just how you feel. A six on the scale is equivalent to lying in bed—there’s no exertion, while a 20 is equivalent to working so hard that you may pass out (hint: you never want to get to 20). When exercising, an exertion between 12 and 14 is indicative of moderate intensity. It’s not too hard or too easy, but like Goldilocks, it’s just right.

While there are many variations of the RPE scale, this 6 to 20 version provides a rough estimate of your heart rate, which is useful if you don’t have a heart rate tracker or don’t want to take time out of your workout to count your pulses. If you add a zero to the end of a number on this RPE scale, it is an approximate measure of your current heart rate. For example, if my perceived exertion during a run is 12, my heart rate is ~120 beats per minute. This scale is ideal for individuals taking meds like beta blockers and ACE inhibitors that can affect their heart rate.

If calculating your THR or using the RPE scale is not for you, there is one more way to assess your exercise intensity while working out, and that is the “talk test”. In general, if you’re working at a moderate intensity level, you are able to carry on a conversation but not sing while performing the activity. It’s as easy as that! Now, who’s ready to work out and track their intensity?