If you’ve ever taken a HIIT or running class, chances are the instructor will ask you to wear a heart rate monitor. Why? The range of your heart rate throughout your workout puts a number to the intensity of the exercise and how hard your body is working.
Heart rate monitors measure your maximum heart rate (MHR) and your resting heart rate (RHR) through built-in sensors. But not all heart rate monitors deliver the same results. Chest straps are generally more accurate than wrist sensors, since (you guessed it) the transmitter on the chest is closer to the heart than the wrist.
Benjamin Reuter, Ph.D, CSCS*D, ATC and associate professor in the Department of Exercise Science and Sports Studies at California University of Pennsylvania, says, “Heart rate is an easy way to monitor intensity of exercise, and you can use it to design a training program that challenges the cardiovascular system and improves aerobic fitness.”
It’s important to remember, though, that everyone’s bodies are different so your heart rate numbers can differ greatly from someone else’s. Those beats per minute depend on many factors, including your fitness level, age, diet, stress levels and even your surrounding temperature and altitude. Here’s everything you need to know before strapping.
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Your Resting Heart Rate
Your resting heart rate, or RHR, will naturally be lower when you’re waking up in the morning compared to sitting or standing up. A wristband heart monitor can fairly accurately measure your resting heart rate while you sleep. You can also measure your own pulse; place the tips of your index and middle fingers just below your bicep on the side closest to your body. Or, place them underneath your jaw on either side of the neck, or on your wrist or temples (right between your hairline and eyes). Count how many pulses you feel in one minute. The number you get is your resting heart rate in beats per minute (BPM).
RHR is also a good way for endurance athletes to ensure they don’t over-train and stay healthy overall. If you’re training for your first marathon and see a sudden spike in RHR, for example, it may be an indication you’re not taking enough recovery time, Reuter says. And for those new to fitness or coming back from a hiatus? “A change in your RHR shows a measure of improvement. When your RHR decreases, it’s an indication that your fitness is improving,” Reuter adds.
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Your Maximum Heart Rate
Now, how hard can you go? Your maximum heart rate (MHR) is the highest heart rate you can achieve through exercise. To measure your max HR, a fitness coach might ask you to hop on the treadmill while wearing a chest strap. The most accurate maximum heart rate equation is 208 – 0.7 x your age for those doing the math at home.
For the average recreational athlete, Reuter says the following treadmill test would provide a good indicator of MHR for running:
Warm-up: Walk or jog for 10-15 minutes and slowly increase your speed. You should be able to hold a conversation.
Interval 1: Run at an all-out sprint speed for 30 seconds.
Recovery Period 1: Rest 60 seconds.
Interval 2: Run at an all-out sprint speed for 30 seconds.
Recovery Period 2: Rest 60 seconds.
Interval 3: Run at an all-out sprint speed for 60 seconds.
During the last interval, you would extend the all-out sprint to a full minute. Record heart rate at the end of this minute. Now that you’ve got your resting and maximum heart rate, it’s time to use these numbers to find your aerobic training zone.
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Calculating Your Heart Rate Training Goals
Everyone’s resting and max HRs will be different, but fitness coaches will use the same heart rate training zones to help their clients improve their endurance.
“If I’m working with an athlete, whether it’s a soccer mom training for a 5K or someone with a goal of qualifying for the Boston Marathon, I use heart rate training zones to improve their athletic performance,” says Reuter.
According to the American College of Sports Medicine’s Guidelines for Exercise Testing and Prescription, the recommended percentage of maximum heart rate range for developing aerobic fitness is 50 to 85 percent. But how do you know when you’re in the zone? You’ll need to first calculate your heart rate reserve, or HRR. The formula: HRR = maximum heart rate – resting heart rate.
Once you know your HRR, you can then calculate your target heart rate by using this Karvonen formula: Target Heart Rate (in BPM) = HRR x exercise intensity + RHR. So to determine your 50 percent target, you’ll plug “50” in as the exercise intensity. Your answer will be the lowest heart rate in BPM you should aim for. Then, to calculate your highest heart rate to improve aerobic fitness, crunch those numbers again using “85” as your exercise intensity.
Your Level of Effort
To help you put the maximum heart rate percentages into perspective, Reuter says this is how most aerobic training programs break down heart rate training zones:
Zone 1: 50-60 percent
Zone 2: 60-70 percent
Zone 3: 70-80 percent
Zone 4: 80-90 percent
Zone 5: 90-100 percent
For example, let’s say your RHR is 44 and MHR is 190. Ideally, you’d want to use the MHR you’ve found doing the above treadmill field test, Reuter says.
Lower Limit Target Heart Rate Formula: 190 (MHR) – 44 (RHR) x 50 percent + 44 (RHR)
Your lower limit is: 117 BPM
Upper Limit Target Heart Rate Formula: 190 (MHR) – 44 (RHR) x 85 percent + 44 (RHR)
Your upper limit is: 168 BPM
In this case, you’d want to do steady state cardio between 117-168 BPM to improve endurance.
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“Unless you have a pre-existing heart condition, if your work to rest ratio is one minute to one minute, you should see your heart rate drop from 90 percent to 70-75 percent by the end of the recovery minute,” Reuter explains. “But if you don’t see your heart rate dropping down to below 75 percent of MHR after 15-16 minutes, that means you’re not giving yourself enough time to recover.”
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Keeping Heart Rate Training in Perspective
Head spinning from all that number crunching? Remember that unless you’re a professional athlete, you don’t need to think too obsessively over heart rate. Instead, think of heart rate monitoring as a tool that allows you to see if you’re improving your fitness over the course of a few weeks and months. Tracking your heart rate, whether on an app or watch, can also break up the monotony of long, steady-state cardio sessions. Plus, it’ll force your heart — and your head — to get in the zone.