Measuring Intensity

Understanding how to measure intensity is a key concept in preparing to be a fitness professional. Before we can gauge how hard our clients are working, we have to know how to measure it. Before we can determine if our clients are whining about working too hard, we have to understand what they should be working at.

In the ACE Personal Trainer manual 3rd edition, pg 219 is where to start.

There are five primary ways to measure intensity. These have been standardized and are recommended for fitness professionals:

• Vo2 – aka Aerobic Capacity
• Heart Rate – either percentage of maximal heart rate or percentage of heart rate reserve (aka Karvonen)
• Rate of perceived exertion – aka RPE
• The ‘talk test’ method
• METS – aka metabolic equivalent.

Of these five ways, personal trainers are least likely to use VO2 and METs. For this reason, we will talk more on the other three methods. When we are establishing a workload for our client, we set a specific range for them to work in: 40% - 60% of HRR, 12 – 14 RPE, 6 – 8 METS, etc. We check in with our clients during their workout to make sure they are operating at this suggested intensity. If not, we make the necessary adjustments.

First, VO2 is a measure of aerobic capacity.

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. Remember that there is Vo2max and VO2R, just like with heart rate. Check pg 218 in the ACE Personal Trainer manual 3rd edition for more details.

Next, we look at heart rate. We are all familiar with using heart rate as a method of measuring/determining intensity.

HR max = (220 – age) x percent of workload

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

Remember that HRR is often considered slightly more accurate than HR max. HRR is currently one of the more popular methods of calculating workloads.

Following heart rate on the list is RPE. 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. 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.

Fourth on the list is the ‘talk test’. This is another subjective measure of intensity that can be very useful in determining exercise workload. We’re all familiar with the ‘if you can’t talk comfortably you are working too hard’ theory of exercise. The talk test is primarily used to determine a comfort zone when working out, especially for those just beginning an exercise program. For those capable of working at higher intensities, this may be a bit limiting.  

Finally, we can measure intensity by METS. A MET is a multiple of someone’s resting oxygen consumption.  Technically speaking 1 MET = 3.5 ml/kg/min. If you check some aerobic exercise equipment you can find a listing for METS on the display. Page 222 of the ACE Personal Trainer manual 3rd edition has more information on METs. However, this is not a commonly used measurement in the general fitness field.

The five 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).

To gain an understanding of how these different factors relate, I would recommend checking out the FITT principle on pg 329, table 11.2 of the ACE Personal Trainer manual 3rd edition. When we are working with a client, we use one of the five listed methods to measure how hard they are working.

For example: the client needs to work at:

55 – 65% of VO2max or 55 – 65% HRmax or 12 – 13 RPE or 40 – 50% HRr or 12-16 RPE.

These numbers all represent approximately the same intensity level. Which method of measuring intensity you choose to use will depend on your preference as well as your client.

If you’ve got questions, just contact one of our Education Consultants at 1-888-825-3636 x782

P.S. - no post on the 28th! Back with new info and study tips in January 2010!