Exercise Intensity: How to Measure it?

The second rule of the “FITT” principle is the three (3) well-known ways of gauging the intensity of exercise.

1. Karvonen Formula

Your heart rate is a convenient, reliable, and personal indicator of how hard your heart is working and the intensity of your exercise training.  Knowing your heart rate helps relates to intensity. It is a measure of how hard you and your heart are working. I will describe you decide whether to increase or decrease the intensity of your exercise training, based on your goals and fitness level.  Although there are many subjective clues indicating how your body is responding to exercise (your perceived exertion, breathing rate, physical sensations), none is as reliable as measuring heart rate. It is objective and affected by both internal and external factors, and is therefore a dependable measure of physical condition.  It is useful for people training at a specific intensity of exercise, or people with certain cardiac risk factors who have been set a maximum heart rate by their doctor.

Karvonen Formula is one of the most effective ways to estimate your target heart rate, because it takes into account your Resting Heart Rate [RHR] (a good indicator of your fitness level). There are various ways of finding resting heart rate.  Next time you are visiting your diabetes educator or health care professional, ask for a demonstration about how to find your RHR by taking your pulse either at your wrist (radial artery pulse) or on the side of your neck (carotid artery pulse).

Wrist – below the base of the thumb (Radial Artery Pulse)

• Find your pulse by placing 2 to 3 fingers on your wrist below the base of your thumb.  Apply light pressure until you feel a heartbeat.
• Count the number of beats you feel in 10 seconds

Neck- below the angle of the jaw (Carotid Artery Pulse)                                                     

“Instant Heart Rate” is an app. you can use on your iPhone by just placing the tip of your index finger on phone’s camera.  Some wear a heart rate monitor which is the easiest way to monitor your intensity because it does all the work for you—all you have to do is look at a digital watch to see your current heart rate in beats per minute and/or percentages.

Applying the Karvonen Formula:

(MHR – RHR) X Intensity of Exercise + RHR = THR

Where,

• MHR = Maximum Heart Rate in beats per minute (bpm) is the fastest your heart can beat (predicted).  It is calculated as follows:
• 220 – your age.  So for a 40 year old person, their MHR is 220 – 40 = 180bpm
• Intensity of Exercise = how hard the exercise will be, expressed as a percentage (%).  Commonly the intensity is set at 50 to 85%.
• RHR = Resting Heart Rate in beats per minute (bpm)
• THR = Target Heart Rate

Example:  How to calculate the Training Heart Rate (THR) range at an intensity of 50 to 60% for a 40 year old person starting a new exercise program.  Resting Heart Rate (RHR) of 75 beats per minute:

THR range = (MHR – RHR) X Intensity + RHR

Step 1. Calculate the MHR

MHR is 220 – 40 = 180bpm

Step 2. Calculate the minimum THR (50%)

(180 – 75) X .50 + 75 = 128 bpm

Step 3. Calculate the maximum THR (60%)

(180 – 75) X .60 + 75 = 138 bpm

Hence as a beginner exerciser HR range is calculated to be 128 to 138 bpm.

You need to periodically check your heart rate throughout your workout to gauge your intensity level. There are two ways to do this:

1. Take your pulse after you’ve been exercising for at least 15 minutes. An easy way to check your pulse without interrupting your workout too much is to take a quick 10-second count and then multiply that number by 6 to get your heart rate in beats per minute. If your pulse is within your THR range, you’re right on track! If you are lower than the minimum, you will need to increase your intensity (speed and/or incline if walking on a treadmill) and count again. If you are higher than THR range, decrease your intensity of exercise by slowing down.
2. You can enter your THR range in your heart rate monitor, periodically check the digital wrist watch to see that you are exercising within your limits.

Additional Tips for Using Target Heart Rate

• As you increase your fitness level, you may have to increase your intensity from 50 to 60 % up to 70 to 80% and recalculate your THR range.
• Some medications (such as beta-blockers) can affect your heart rate during exercise. An exerciser taking beta-blockers may be working at a high intensity but might never reach his/her target heart rate range. Therefore, people on this or similar cardiac medications should not use the Karvonen Method to calculate their THR range and would need to use alternative methods of gauging intensity described below.

2. Rate of Perceived Exertion (RPE) Scale

This is an individualized method of judging intensity because it depend on your own perception of how hard you are exercising. It was designed by a Swedish psycho-physiologist Gunnar Borg, hence named Borg Scale. Being a psychophysiological scale, it calls on the mind and body to rate one’s perception of effort.

RPE	Description	Intensity Level
7 8 9 10 11 12 13 14 15 16 17 18 19 20	Easy   Very Light   Fairly Light   Somewhat Hard     Hard   Very Hard Very, Very Hard	50% MHR   60% MHR   70% MHR   80% MHR   90% MHR

When using this scale, it is important to remember that “The feeling during exercise should reflect how heavy and strenuous the exercise feels to you, combining all sensations and feelings of physical stress, effort, and fatigue. Do not concern yourself with any one factor such as leg pain or shortness of breath, but try to focus on your total feeling of exertion.”

3.The Talk Test

The final method for measuring exercise intensity is the Talk Test. Like the RPE, the talk test is subjective and quite useful in determining your exercise intensity, especially if you are just beginning an exercise program.

Work at an intensity that allows you to breathe comfortably and rhythmically throughout all phases of your workout. This will ensure a safe and comfortable level of exercise. If you are breathless, or can’t talk, you’re working too hard! Lower the exercise intensity. If you experience dizziness or light-headedness, you may be overexerting yourself and should stop.

The Talk Test has been confirmed as a simple and accurate method of gauging intensity that doesn’t require any equipment or special training. Try your own Talk Test during your next workout (and compare it to your Target Heart Rate if you’re skeptical).

If you like technology and care about the numbers, a heart rate monitor might be a useful device for you. If you feel you’re in tune with your body and your level of exertion, you likely will do fine without a monitor using the last two methods described above.