Whether you're looking to lose weight, improve aerobic fitness, muscle strength, or endurance, exercise intensity will be an important factor and needs to be considered when trying to reach your health and fitness goals.
Exercise intensity refers to how much energy is expended during exercising. In the most simplistic terms - it’s how hard your body is working.
Intensity can be measured subjectively (based on a “feeling” scale) or objectively (such as through a heart rate response). A talk test may also be used to measure intensity and is a practical application, since it’s relative to an individual and requires no equipment.
I use a combination of all of the above with my clients and what method is dominant depends on who I am working with.
As a trainer and CEP, I know what a heart rate (HR) response means on a physiological level. For this reason, the metric guides me to progress them safely towards their fitness goals.
However, using HR to establish intensity isn’t right for everyone.
If you don’t have a fitness tracker that measures HR or if you are on medications that suppress your vitals (i.e. beta blockers), then using a “feeling” scale or a talk test is a better option.
Measuring exercise intensity by “how you feel”
To measure exercise intensity subjectively, you can use a Borg Rating of Perceived Exertion (RPE) Scale or a modified RPE scale. There are slight differences between the two RPE scales.
The original Borg RPE is based off how hard you feel you're working and you're heart rate. The ranges fall between 6-20, with 6 being no exertion and 20 being the most vigorous exertion possible. If you take a zero and plant it behind one of the numbers on the scale it's supposed to represent where your heart rate is for that given activity. This scale makes sense to me, but is not always cognitively easy for clients to translate.
The modified RPE scale has a range from 0-10, with 0 being no exertion and 10 being maximum exertion. This scale corresponds with a feeling of breathlessness.
I always recommend erring on the side of caution when using these scales. After you get clearance from your doctor (important), then I recommend exercising at a low to low-moderate intensity such as a Borg RPE of 9-12.
Once you get stronger and build stamina, you can progress to a Borg RPE of 12-16. Even after building a fitness baseline, I recommend being careful exercising above a RPE of 12-16. In my experience, working at a RPE of 17 or higher isn't necessary to establish and maintain fitness levels. Also, depending on your health status, that high of an exercise intensity may be contraindicated.
Keep in mind, as intensity increases, your risk for injury does as well. Please be careful and listen to your body!
Measuring exercise intensity by heart rate
To measure exercise intensity objectively you need some form of heart rate (HR) device, such as a chest strap or fitness tracker (i.e. Apple Watch, Fitbit, or Garmin). Most fitness devices used for exercise tracking also come with a companion app. Together they categorize your exercise efforts based on your current health status and the health information collected when activating your device (i.e. height and weight).
Last time I researched fitness devices many of them categorized intensity training zones differently and the formulas varied. You can find out how your device derives at your intensity zones by exploring the companion app that comes with the device. If you don’t want to do that, I can give you a simple way to come up with the zone you’re working in based off your heart rate response.
The most simplistic and “user friendly” formula to measure aerobic intensity is based off of your heart rate max (HRmax), which is also known as your age predicted max heart rate (APMHR). Age is the only factor taken into consideration when using this formula.
To figure out your HRmax subtract your age from 220.
Then take that number and multiply it by the % intensity you want to work in.
For example:
If I want to work at a moderate intensity according to the HRmax formula, American College of Sports Medicine (ACSM) states I should work at 64-76% of my HRmax.
So, it would look like this:
220-46=174 bpm (my HRmax)
174 x .64= 111 bpm (low end of moderate intensity)
174 x .76= 132 bpm (high end of moderate intensity)
Therefore, my HR needs to be in a range of 111-132 bpm to be exercising at a moderate intensity according to the HRmax formula.
Keep in mind HRmax formula isn’t a relative formula, so it may not be well suited for individuals that are older, deconditioned, or those with chronic diseases. Formulas using an individual’s resting HR or VO2 (maximum oxygen consumption measured during exercise) may be more appropriate. A simpler metric would be a talk test. This is easy-if you can carry on a conversation, this may be a good intensity for you to exercise. If you’re not able to talk, then you may need to dial it back a bit.
Measuring strength training intensity is a little more complicated, especially if you’re a novice lifter.
Strength training is about volume (sets and repetitions) and load (the amount of weight you’re lifting). The number of sets, reps, and load you lift will depend on the goals you have set for yourself. Many people want to increase muscular strength and endurance, while power is generally for more sport specific training.
I try to keep it simple when talking to my clients who are performing resistance training for the first time or haven't touched weights in a while. Pick a weight that you can keep proper form with and are able to execute a full range of motion so the entire muscle is activated. Also, the weight should have you feeling a little “wobbly” (fatigued) in the muscle being worked by the end of the last set (and it’s ok not to finish the last couple reps in the set.) Also, if you’re not “wobbly” by the last set, then increase your weight!
Take Home
Exercise intensity is an important factor to consider when trying to reach health and fitness goals. There are a variety of ways to measure how hard you're working during exercise.
The measurement you pick should be based off your health status and your access to the measurement method. If you have certain medical conditions or don't own a heart rate monitor, then a simple talk test or RPE scale may be better suited for you.
No matter how you’re monitoring your exercise intensity, you should always listen to your body and play it safe. Start working at a light to moderate intensity until you get stronger and build up stamina. Vigorous intensity is NOT appropriate for you if you’re just starting an exercise program and may be contraindicated depending on your current health status.
Also please remember to always consult your doctor before embarking on an exercise program!
Please let me know if you have any questions and sweat on!
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