Exercise Intensity scales
There are several different exercise intensity scales that can help you get a better understanding of what intensity you are working out at. Some are less specific than others, as exercise intensity is a very subjective experience. You can be more specific by calculating your target heart rate zones and purchasing a smartwatch, or be less specific by relying on the Borg intensity scale or the Talk test. Read more below to find out what’s best for you!
1. The Talk Test
The Talk test is a common way of quickly assessing your current intensity level. It assumes that there is a linear relationship between your breathing frequency and your training intensity (e.g. the harder you work, the higher your breathing frequency). Despite being a non-specific test, the talk test is a quick, easy and reliable method of judging your approximate exercise intensity
- Light intensity = There is no significant change in breathing rate. You should be able to hold a conversation without having to take breaks to catch your breath.
- Moderate intensity = There is a slight change in breathing rate. You may be breathing a little faster and your speech may be affected slightly. You should, however, be able to keep a conversation uninterrupted.
- Vigorous intensity = You have significant difficulties speaking more than 1-2 sentences without having to take a break to catch your breath.
Why is there such a big difference between moderate & vigorous intensity?
You may be asking yourself why there is such a sudden increase in breathing frequency when switching from moderate to vigorous intensity exercise. This is due to a sudden increase in lactate build-up within the bloodstream. The point at which this occurs is called OBLA (onset of blood lactate accumulation). This happens because your muscle fibres are starting to switch over to using a different energy system, as the one you were using before is not providing you with sufficient energy to complete the task at hand [4]. A by-product of this switch in energy systems is lactate, which produces more hydrogen ions, making our blood more acidic. This in turn, can decrease your body’s pH levels (a measure of how acidic/basic a fluid is). Your body likes to operate at a blood pH of 7.35 – 7.45. Lactate makes our blood more acidic (lowers your pH levels) through the production of hydrogen ions. Hydrogen ions can be cleared by the lungs. We try to get rid of these Hydrogen ions by breathing faster.
2. Heart Rate Monitors
Believe it or not, but your body has a built-in system to monitor your exercise intensity – your heart. Your heart rate will increase proportionally to the increase in exercise intensity until it reaches ~80% of its maximum. Adding this to the fact that it is a comparably easy physiological sign to monitor manually (more on this later in this article) or automatically through heart rate monitors, we can use it to properly prescribe and reliably monitor exercise intensity.
Heart rate monitors have gained significant popularity in the past decade. In fact, 1 in 5 Americans reported that they owned a smartwatch or another digital device that tracks their fitness [1]. This is great news! Now we just need to know how we can use this data to analyze our workouts more in-depth.
What Heart Range should I Aim for?
If you are wondering what exercise intensity is best for you to achieve your goals (light, moderate, vigorous), I suggest that you read our article What Exercise Parameters Are Right For Me?
Once you know what intensity is right for you, it is time to learn about your ideal heart rate range to know you are actually training at the appropriate intensity. Your target heart rate is dependent on factors such as your age and current physical conditioning level. We should attempt to be accurate in order to avoid overtraining, as well as wasting our time. To find out your ideal heart rate ranges, we will have to perform a slight bit of math (see below).
Calculating Your Ideal Heart Rate Ranges
It all comes down to this formula – The Karvonen Formula. All values (HRmax, HRrest, intensity) depend on your goals and personal factors, so let us have a look at how we can identify the three unknowns from this equation.
- Intensity (moderate → 40-60%, vigorous → 60-80%) = As you will want to work within a specific heart rate range during your workout, you will need to perform the above equation twice – once to calculate your lower threshold (40% for moderate and 60% for vigorous), and the second time to find out your upper threshold (60% for moderate and 80% for vigorous). For your heart rate’s lower threshold, plug in the intensity % as a decimal – e.g. for 40% intensity type in 0.4 (or 0.6, respectively) into the equation and for your upper threshold put 0.6 (or 0.8, respectively).
- Resting Heart Rate (HRrest) = Quickly find out what your resting heart rate is by following the three steps below. The best time to find out your resting heart rate is immediately after getting out of bed. Avoid having coffee, stressful activities or performing exercise before doing this as your heart rate reading will likely be higher than your true resting heart rate.
1. Set a timer for 30 seconds
2. Palpate your resting heart rate by placing your index finger about one inch above your wrist crease on the thumb’s side (onto your radial artery). Make sure to not press too hard or you will have trouble finding it. Start the timer and count the number of pulses (e.g. counting 28 beats during 30 seconds)
3. Multiply the counted number by two to get your resting heart rate (e.g. 28 x 2 = 56 bpm = HRrest)
- Age-related Maximum Heart Rate (HRmax) = To find out your age-related maximum heart rate, simply put your age into the following formula: 206.9 – 0.67 * Age. For example, the maximum heart rate for someone that is 30 years old would be 187 bpm (as 206.9 – 0.67*30 = 187)
Example
A hard-working 30-year old father of two is looking to get started on a vigorous exercise program to save time and take advantage of the benefits of high-intensity exercise. He counts a resting heart rate of 56 and an age-related maximum heart rate of 187. His ideal heart rate range would be as follows:
Target Heart Rate = [(HRmax – HRrest) * Intensity] + HRrest
- Target Heart Rate (lower threshold) = [(187 – 56) * 0.6] + 56 = 135 bpm
- Target Heart Rate (upper threshold) = [(187 – 56) * 0.8] + 56 = 161 bpm
3. Heart Rate Palpation
Get a rough estimate of your heart rate by turning your timer on for 15 seconds. Place your index finger about 1 inch above your wrist crease on your thumb side (as described above). Ensure to not put too much pressure onto your wrist or you will have difficulty finding it. You can also perform this on your neck by palpating your carotid artery by your neck. This method works better if you are in between exercise sets or you are taking a short break. For most accurate results, perform this method immediately after you stop exercising, as your heart rate will slowly lower the longer you are into your break.
4. Ratings of Perceived Exertion (Borg Scale)
A further accurate and quick way to measure perceived exertion without paying attention to your heart rate readings is the Borg Intensity Scale. It was developed by researcher Gunnar Borg. The scale categorises exercise intensity based on your perceived exertion as you are performing your exercises. Rather than a 1-10 intensity scale with 1 referring to very low intensities such as sitting or standing and 10 being maximal exertion, it is based on a 6-20 scale.
Why? The reason being that these numbers (multiplied by 10) are representing your approximate heart rate in the moment. It is assumed that your rating of perceived exertion of 12, for instance, corresponds with a heart rate of approximately 120 bpm, which corresponding with moderate intensity exercise (see below for intensity ranges). Typical resting heart rates typically range from 50-70 bpm and with vigorous exercise between 160-180 bpm. For more individualized heart rate zones make sure to calculate your ideal heart rate zones through the calculations provided above. The scale assumes a close relationship between your heart rate and your perceived exertion.
Consistently evaluating your exertion level as you are exercising based on this scale will help you judge your level of exertion and may be the quickest way to assess it. You may find it difficult to do using the Borg scale at first, but that is normal. I promise that you will get better at it over time.
What Borg Range should I be aiming for during my Workouts?
It is important to be aware that your normal heart rate varies throughout your lifespan and that it is based on your age and physical conditioning. Below you can find your typical heart rate intensity zones. As mentioned before, use our calculations shown above to know what range is most suitable for your needs.
- Low intensity = 6-11
- Moderate intensity = 12-14
- Vigorous intensity = 15-17
Personal Preferences
I prefer to work out at higher intensities. I am currently in a very busy part of my life, just having started my career and being in a serious relationship. I use the heart rate monitor on my smartwatch during interval training and the Borg intensity scale during low-speed resistance training. What are you using, and why? E-mail me at [email protected] and let me know!
Conclusion
Adding sufficient intensity to your workout is the most important variable to training success. Therefore it is greatly important to continue checking in whether or not you are working our hard enough. Luckily, there are multiple ways of judging exercise intensity. Our heart provides us with plenty of signals. We have developed formulas such as the Karvonen formula that give us a great idea of how hard we need to be exercising to achieve our desired results, and we have developed scales such as the Borg perceived intensity scale and the talk test to provide us with a rough estimate of our current exercise intensity.
References
[1] Vogels, E. A. (2020, August 14). About one-in-five Americans use a smart watch or fitness tracker. Pew Research Center. Retrieved September 20, 2021, from https://www.pewresearch.org/fact-tank/2020/01/09/about-one-in-five-americans-use-a-smart-watch-or-fitness-tracker/.
[2] ACSM Exercise Guidelines. (2010). Acsm.Org. https://www.acsm.org/blog-detail/acsm-certified-blog/2020/09/03/acsm-exercise-guidelines-resources
[3] McArdle, W. D., Katch, F. I., & Katch, V. L. (2014). Exercise Physiology: Nutrition, Energy, and Human Performance (8th ed.). LWW.
[4] Wilmore JH and Costill DL. (2005) Physiology of Sport and Exercise: 3rd Edition. Champaign, IL: Human Kinetics