Consider this: The CDC recommends adults get at least 150 of moderate intensity or 75 minutes of vigorous intensity exercise a week. So, what exactly does moderate and vigorous mean? And how can you know if you’re exercising at the right level of intensity?
“Exercise intensity is the key to effectiveness of training, and to some degree safety of training. There’s a range where you get the most benefit with the least risk,” says Wayne Westcott, Ph.D, professor of exercise science at Quincy College. “There are several studies that show if you go below that range, for example walking at a slow pace, it doesn’t have much benefit in terms of burning fat or cardiovascular conditioning. But if you go too fast, for example sprinting, you won’t be able to exercise for very long and you’ll have a higher risk of injury.”
When you lace up for a workout, you want to be as efficient and effective as possible. Exercise doesn’t always feel the same, and it can differ day to day, from person to person. Understanding how different intensities feel and how to use them can be helpful in improving cardiovascular fitness, benchmarking improvements, and even getting the most out of a quick workout—despite the fluctations.
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Measuring Exercise Intensity: Heart Rate vs. RPE
Exercise intensity is determined by heart rate, but can also be measured by breath, muscle fatigue and sweat. The faster your breath and heart rate, the higher the intensity. During a moderate workout, you want to work hard enough for your heart rate to be between 50% and 70% of its maximum.
There a few things you need to know to accurately measure intensity using heart rate. First, you need to know what your maximum heart rate is—the limit of what your heart can handle during physical activity. By subtracting 220 from your age, you can figure out what that max is. While this is a good guide, it’s a very general range that can vary greatly from person to person, says John Porcari, Ph.D, member of the scientific advisory panel for the American Council of Exercise.
“We don’t use heart rate a whole lot anymore, because they can be so variable. The only way to know exactly what someone’s maximum heart rate is would be to put them on a treadmill,” he says. “When you predict it (subtracting your age from 220) there’s a large scatter of what that heart rate might actually be.”
The second way to measure exercise intensity is to use the rate of perceived exertion (RPE), which focuses on how hard you feel you’re working to determine the level of intensity. The Borg Scale is used to gauge perceived exertion with a range of 6 to 20, 6 being no exertion and 20 being maximal exertion, a simpler scale of 0 to 10 is now also used.
RPE is a simpler, subjective measurement, which means you have to pay attention to how your body feels during each exercise. Two people doing the same exercises can have different levels of perceived exertion, and as you as you become more active, your perceived exertion changes over time.
“It’s going to vary for everyone and it’s going to vary from day to day. One day you may be rested and feeling strong, and another might be a hard day with a lot of stress, which is why perceived exertion is a great tool of measurement because it focuses on how you’re feeling in that moment,” says Westcott.
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So, how can you tell if you’re exercising at a moderate or vigorous level? When doing aerobic activity like walking, jogging or cycling, the talk test can be used to determine intensity.
The Talk Test
Porcari and researchers in the department of exercise and sport science at the University of Wisconsin-LA Crosse validated the talk test, which identified the point where talking becomes challenging, but not impossible. They tested this by asking participants to recite a passage every five minutes while cycling, if they were able to speak comfortably, resistance was increased, if the participant responded no, resistance was slightly decreased. It is at this point that you’re exercising at an intensity that yields the most benefit. As intensity increases, your breathing also increases which makes talking more difficult.
How to use the talk test to identify RPE
Want to try it for yourself? Just hop on a treadmill, bicycle or start walking outside.
Step 1: Begin with 5-minute light warm-up, think of a leisurely walk, which is around 2 to 3.5 mph on a treadmill or an RPE of 2 to 3 (see table below).
Step 2: Once your body is warmed up, start at a low exercise work load, exercise for two minutes, then recite the Pledge of Allegiance.
Step 3: Ask yourself, “Was it easy, uncomfortable, or difficult to recite?”
Step 4: If it was easy, increase the speed, hold that speed for 2 minutes and then recite the Pledge of Allegiance again.
Step 5: Keep repeating steps 2 through 4, until you reach the point that you can no longer speak comfortably. When you reach this point, back off your speed a little bit. You’re at a moderate level of exercise if that can be maintained for at least 30 minutes.
Step 6: Within 30 minutes following the workout, rate it overall on a scale of 1-10.
You can also use these steps on a bicycle and increase resistance or speed or walking outdoors by increasing speed. If you don’t want to recite the Pledge of Allegiance, try singing along to your favorite song instead.
Once you get a feel for how your body feels at different intensities, you can begin to experiment with higher levels of intensity by using the steps above. Once you reach the point that you can no longer speak comfortably, try exercising at that pace for a short period and then recovering in the moderate zone below.
Remember, as your endurance and cardiovascular fitness improve, your perceived level of exertion will change at different speeds and resistance. But, the only way to improve is to push the system, says Porcari.
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Guide to RPE and the talk test
| Scale | What it should feel like | Talk test cues |
|---|---|---|
| 0 | Nothing at all. You’re sitting on the couch reading a book. Heart rate is resting. | You could sing the Pledge of Allegiance for hours. |
| 1 | Very light. You’re folding laundry with a little effort. | You could sing and continue folding laundry all day long - though you probably don’t want to. |
| 2 | Light. You’re walking casually around the house, not enough to increase heart rate or breathing. | You can recite the entire Pledge of Allegiance easily and carry a conversation. |
| 3 | Moderate. You’re walking like you’re trying to catch a bus. This is where your heart rate and breathing begin to increase. | You can recite the entire Pledge of Allegiance easily with a little breathiness. |
| 4 | Somewhat hard. You’re slightly uncomfortable, walking quickly but not overdoing it. You begin to sweat after about 10 minutes, but you’re not out of breath. | You can recite the entire Pledge of Allegiance easily with a little breathiness. |
| 5 – 6 | Hard. This is your moderate intensity workout. You’re sweating, slightly breathless, but not extremely uncomfortable. | Can talk, but only a short string of words interrupted by breath. Talking is challenging, but not impossible. This is the point where you would slightly decrease speed for a moderate workout, or slightly increase speed for a short period of time for a higher intensity workout. |
7 -9 10 | Very hard. This is your vigorous workout. The highest level of activity you can sustain for a short period of time. You begin sweating after only a few minutes. Very, very hard. You’re running from a guerilla and can’t possibly run any faster. You can only work at this level for a short period of time, no more than a couple of minutes. | Can barely spit out, “I pledge allegiance…” without gasping for air. Or may only be able to grunt in response to questions. Can’t speak at all. |
Using RPE with Strength Training
Cardiovascular fitness isn’t the only thing you can do to improve overall health and fitness, strength training can help develop strong bones, lean muscle mass, and even help manage chronic conditions like arthritis and back pain, according to the Mayo Clinic.
Just like aerobic training, knowing how to measure intensity while strength training is going to help you get the most benefit with the least risk.
Originally the Borg Scale was only used for aerobic activities like walking and swimming, but recently RPE has been used effectively with resistance training based on the number of repetitions able to be performed until muscles have reached their fatigue point.
When you’re lifting free weights or using a machine, start with a lighter weight and see how many repetitions you can complete. Aim for at least 8, but no more than 12. That middle range between is where most people would be working within 70 to 80% of their maximum strength, says Westcott. If you can easily complete 12, increase the weight until you’re within the 8 to 12 range.
“Most national organizations would recommend that if you can’t do at least 8 repetitions the weight is probably too heavy. But, if you can do more than 12, the weight is probably too light to give you benefits,” he says.
Resistance training and RPE
| Rating Perceived Exertion | |
| 1-2 | Can lift the weight with little to no effort. |
| 3-4 | Can lift the weight with light effort; able to do approximately 15-25 repetitions before muscle feels fatigue. |
| 5-6 | Feel that you can lift only 4-6 more repetitions. |
| 7 | Feel that you can lift only 3 more repetitions. |
| 8 | Feel that you can lift only 2 more repetitions. |
| 9 | Feel that you can lift only 1 more repetition. |
| 10 | Maximum effort. Cannot do another rep if you want to. |
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So, next time you head out for a workout, whether you’re going for a jog or doing a kettlebell workout, check in with your body and give RPE a try.