Monitoring Exercise Intensity

Exercise intensityMonitoring exercise intensity is one of the most important factors that determines if your workout is effective or not. Whether your goal is to lose weight or improve your endurance, you should keep track of your exercise intensity when you want results. For cardio training the most accurate way to measure exercise intensity is the oxygen uptake. However this requires expensive and often cumbersome equipment to be practical in everyday training. Fortunately there are three other ways that can be used effectively during your workout.


Heart rate
When you exercise, your heart rate increases to meet the increased blood flow demands to supply your muscles with oxygen and nutrients. The harder you exercise, the more oxygen and therefore blood flow is needed and your heart rate rises with it. Your heart rate is therefore a good indication of how hard you are exercising. Many exercise guidelines will advise you to exercise at a certain percentage of your maximum heart rate (MHR). They categorize this mostly as “Light”: less than 65% of maximum heart rate, “Moderate”: 65%-75% of maximum heart rate and “High”:75%-95% of maximum heart rate. And 95%-100% is considered “Maximum”.

To measure heart rate during exercise, you need a heart rate monitor and many are commercially available for reasonable prices. Mostly they use a band that goes around the chest and measures the heart rate and a watch that catches the signal the band gives off and displays a heart rate. In addition, it is also possible to have a band that works with your smartphone when combined with an app.

When you want to train at a certain percentage of your maximum heart rate, you must first now that maximum heart rate. This poses several difficulties. The first and most reliable way is to measure your heart rate while going all out on your preferred cardio machine. However, for most it is unwise to go 100% all out without any professional supervision and often people are not able to push themselves far enough to reach 100% of maximum heart rate. In addition, the maximum heart rate you will achieve can differ between cardio machines because they do not use the same amount of muscle mass. For example the maximum heart rate on a stationary bicycle will be lower than when running on a treadmill. And your maximum heart rate can vary a little from day to day. The second method is by calculating your maximal heart rate. The most well known method is 220-age. This method is highly inaccurate and your true maximum heart can differ by as much as 14 beats per minute. Other calculation methods are available as well with smaller deviations, but the problem remains the same.

A large drawback of using the heart rate is that when someone gets fitter, that person can tolerate higher heart frequency’s than before. So, in essence 75%-80% of maximum heart rate can shift from “High” intensity to “Moderate” intensity in terms of training effects.

Pro’s:

-Easy to use with a heart rate monitor.

-When based on true measured maximum heart rate, very useful.

Cons:

-Measuring maximum heart rate is difficult.

-Calculating maximum heart rate is generally unreliable.

-Heart rate monitor necessary.

-When getting fitter people are able to tolerate higher heart rates.

Rate of perceived exertionBorg Scale
The rate of perceived exertion or RPE is a subjective scale of exercise intensity. The first one was developed by Swedish Psychologist Gunnar Borg and this remains the most well known RPE scale, the Borg Scale. These scales depend on how people experience the exercise intensity. When exercise intensity increases, heart rate and breathing, muscle fatigue and other symptoms occur. Research has shown a strong connection between the rate of perceived exertion and symptoms that occur as a result of increasing exercise intensity such as heart rate, oxygen uptake and anaerobic threshold.

The standard Borg scale is a 6-20 scale where 6 indicates no exertion at all (rest), 11-13 corresponds with “Moderate” or conversation pace intensity (see below) and 20 indicates maximum exertion. Other scales from 1-10 are also available and perhaps work even better.
Using a rate of perceived exertion gives a very good indication whether someone is training hard enough, however it remains a subjective value and does depend on exercise experience. When someone has never gone all out, that person is far more likely to overestimate the current exercise intensity. However, when coupled to a heart rate monitor, trainers can educate their clients to push themselves further without compromising safety.

Pro’s:

-Very easy to use, especially when subject has experience with the scale.

-Cheap.

-Subjective, when people feel well they might push themselves further than a corresponding heart rate would let them.

Cons:

-Persons with little exercise experience might overestimate training intensity.

-Subjective, inexperienced people might push themselves not far enough to reach the required training stimulus because they are afraid of the increased heart rate or discomfort that comes with training.

Talk Test

Finally the talk test is another way to measure exercise intensity. This is a simple test to use during exercise and you do not need any equipment or even instruction of the person that is training. When using the Talk Test, the person exercising is required to speak. When that person can comfortably speak three to five words with each breath during exercise, the ventilatory threshold is not reached and exercise intensity is “Moderate” or lower. When someone is not able to speak even two or three words during exercising without pausing to breathe, that person is training at a “High” intensity. A large advantage of the talk test is that it depends several physiological processes. Which essentially means that when you are unable to speak easily, you have an effective workout. This remains true, independent of fitness level. When you do not have enough air to speak, you are training effectively.

Pro’s:

-Cheap.

-Easy to use.

-Independent of Fitness level.

Cons:

-Not very accurate

References:

-Roy, B.A. Monitoring Your Exercise Intensity. ACSM’s Fitness & Health Journal 2015, 19, 4.