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Measuring Intensity

Measuring Intensity | April Merritt | Exam Preparation Blog | 1/24/2011


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So…how hard are you really working?

Understanding how to measure intensity is a key concept in effective programming for your clients. But before we can gauge how hard our clients are working, we have to know how to measure their effort.  If our clients are whining about working too hard, we have to understand what they should be working at and why.  If you are following along at home, pg. 375 in the ACE Personal Trainer manual 4th edition is where we start.

There are several ways to measure intensity, some of which are better than others. Below are the ones we will talk about today:

  • Heart Rate – either percentage of max heart rate or percentage of heart rate reserve (aka Karvonen)
  • Rate of perceived exertion – aka RPE
  • Vo2 – aka Aerobic Capacity and METS – aka metabolic equivalent
  • Ventilatory Threshold – VT1 and VT2, as determined by the talk test

So which one of those is best for you? Keep reading!

Heart Rate

First, we’ll look at heart rate. We are all familiar with using heart rate as a method of determining intensity. There are formulas for both heart rate max and heart rate reserve.

HR max:

 (220 – age)  = Max Heart Rate is the familiar and traditional method of measurement. However, researchers have found that it isn’t as predictive as originally thought. One solution was to introduce another max heart rate formula which could be considered more accurate. This equation was the Tanaka formula of 208 – (0.7 x age) = Max Heart Rate

When programming for intensity, a trainer takes the max heart rate value and multiplies it by the intended exercise intensity to determine the exercise heart rate goals. But one of the challenges with using Max Heart Rate is that it doesn’t take into account an individual’s fitness level.

Enter the Karvonen/Heart Rate Reserve formula. HRR is one of the more popular methods utilized to calculate workload intensity. Karvonen includes an individual’s resting heart rate into the equation, which can allow for a more accurate prediction. The HRR formula is as follows:

HR reserve = [(220-age)-resting heart rate)] x intended percent intensity, then add back in resting heart rate.

Examples? How about we use a 30 year old man, with a 65 bpm resting heart rate, and exercise him at 70 % intensity. The examples below will show you how the different equations produce varied results for the same guy.

MHR 220 – 30 = 190 bpm x .7 = 133bpm

MHR Tanaka 208 – (0.7 x 30) = 187bpm x .7 = 131 bpm

Karvonen (220 – 30) – 65 = 125 bpm  x .7 = 87.5bpm + 65 bpm = 153 bpm


Rate of Perceived Exertion

Following heart rate on the list is Rate of Perceived Exertion. RPE is a subjective measure of how the client feels, taking into account psychological factors, musculoskeletal factors, and environmental factors. There are two RPE scales; the BORG scale and the revised BORG (pg. 378, Table 11-4). Explaining how the RPE works is vital when using this tool, so clients can accurately express their workload. If used correctly, the RPE response correlates well with cardiorespiratory and metabolic factors such as heart rate and oxygen consumption.


VO2 and METS

Of the ways presented to measure intensity, personal trainers are less likely to use VO2 and METs.  VO2 is a measure of aerobic capacity, and is discussed initially in the Essentials Manual. The formula for VO2 Is below.

VO2 = cardiac output x oxygen extraction (aka VO2 = Q x A-V O2 diff)

The posts here and here talk a little more about aerobic capacity.  Although we discuss VO2 in the manual, we don’t use it much in the day to day operations of a personal trainer because to be accurate, VO2 depends on a maximal or submaximal test.

A MET is a multiple of someone’s resting oxygen consumption.  Technically speaking 1 MET = 3.5 ml/kg/min, and for many people METS are easier to understand/relate to exercise than VO2. If you check some aerobic exercise equipment you can find a listing for METS on the display.  However, this is not a commonly used measurement in the general fitness field.  Page 378 – 381 in your Personal Trainer Manual 4th edition is where you can find more details on VO2 and METS.


Ventilatory Threshold – VT1 and VT2

Finally on our list we have ventilatory threshold, a new topic with the release of the 4th edition.  We use the traditional ‘talk test’, a subjective measure of intensity, to determine exercise workload via the determination of VT1 and VT2.  I’m not going to go in depth here because I just did a big post on Understanding VT1 and VT2 that covers all the basics.

Although ventilatory threshold can be a bit ‘fuzzy’ and subjective with regards to setting training intensities, you may find that it is actually the most accurate for the greatest number of clients. Like Karvonen, the VT takes into account the individual you are working with. Like RPE, the VT/Talk Test allows for subject input on how hard they feel they are doing. But like RPE, the Talk Test requires careful instruction and monitoring to make sure it is an accurate representation of intensity.


The methods of measuring aerobic intensity, as listed above, are related to each other but not directly equal. It’s an apples to oranges comparison. Apples and oranges are both fruit. HR and RPE are both intensity measurements. But an apple is not exactly the same as an orange. And HR (measured objectively in bpm) is not exactly the same as RPE (measured subjectively with the BORG scale). Which method of measuring intensity you choose to use will depend on your preference as well as your client’s experience and goals.

If you’ve got questions, just contact an Education Consultant at 1-888-825-3636 x782