How to Measure Intensity
Intensity is how hard your heart and lungs are working during aerobic activity. Brisk walking is a moderate-intensity exercise for most people; running is high-intensity. Though high-impact activities are generally also high-intensity, low-impact activities may be low, moderate, or high in intensity.
There are many ways to measure the intensity of aerobic activity. The intensity of aerobic activity can be measured by heart rate (see how to take your pulse and the heart rate chart shown below) and/or by the way you feel during the activity. Both these methods measure relative intensity.
The level of Intensity of a particular activity is relative to a person's level of fitness. Two people of different fitness levels can go for a walk together and be working at different levels of intensity. As you get fitter, you don't have to work as hard to perform the same activity.
Measuring Intensity by How You Feel
One way to measure how hard you are working is by how you feel (perceived exertion) - how deep you are breathing, can you can carry on a conversation, are you perspiring, and what your overall level of fatigue is.
It is important to take into consideration how you feel as a whole. Going by one marker alone may not be reliable. For example, how much you perspire is affected by the outside temperature and humidity, and some people perspire more than others, even at the same level of exertion.
Light-intensity aerobic activity such as slow walking is a good starting point for people who have been inactive, with the goal to gradually work up to the recommended level of moderate-intensity and/or vigorous-intensity aerobic activity needed to provide significant health benefits (e.g. increase aerobic capacity and reduce the risk of heart disease, type 2 diabetes, depression).
Moderate-intensity aerobic activity such as brisk walking causes you to breathe more deeply but allow you to carry on a conversation. Your heart rate will be increased but you may not be aware of it.
Vigorous-intensity aerobic activity such as jogging or running causes you to breathe much more deeply and be limited to saying a couple of words at a time before pausing for breath. Your heart will be beating much faster and you will likely be perspiring heavily.
Note: Vigorous-intensity aerobics need not be high-impact. High impact aerobics involve both feet being off the ground at the same time. Low-impact aerobics always have one foot on the ground. Though high-impact activities such as jogging and running are also high-intensity, low-impact activities can also be of vigorous-intensity. Increase the intensity of a low-impact workout using an elliptical trainer or treadmill by increasing your pace and/or resistance of the machine.
Measuring Intensity by Heart Rate
It is fairly simple to learn to take your pulse (see table below), and most people soon get to know how hard they have to exercise to reach their target heart rate. Once familiar with how hard to work to achieve your desired heart-rate, you can go by how you feel most of the time. Occasionally check your pulse as you will have to work harder to get your heart rate up as you become fitter. Many people combine both methods.
Moderate-intensity aerobic activity is approximately 50 to 70 percent of maximum heart rate.
Vigorous- intensity aerobic activity is between 70 to 85 percent of maximum heart rate.
(Maximum heart rate (beats per minute) is approximately 220 minus your age)
*A target heart rate of 60 to 80 percent of estimated maximum heart rate is commonly recommended to derive the most benefits from an aerobic workout. Keeping the heart rate at about 60 percent of maximum is safer for people who may have undiagnosed heart problems and can be just as beneficial as high-intensity aerobics.
Taking your pulse ensures you are working within your target heart rate. Taking your pulse manually or using a heart-rate monitor during exercise is a good way to learn how to judge how intensely you are working.
How to Take your Pulse (Measure Your Heart Rate)
Note: If you pause to take your heart rate during exercise, take it immediately as your heart rate quickly gets lower with rest.
Lightly press two fingers on the inside of your wrist, just above the base of your thumb. Use a watch with a second hand and count the beats in 10 seconds. Multiply by 6 to get the beats per minute. Alternately, you can take your pulse for 20 seconds and multiply by 3.
Taking your pulse for 60 seconds (or 30 seconds and multiplying by 2) is fine when taking your resting heartbeat. During exercise, you usually have pause to take your pulse. Since your heartbeat slows down quickly when you rest, taking your pulse over 60 seconds will result in an accurate (lower) reading.
You can also use a heart rate monitor that you wear on your wrist, which usually gives a reading within seconds.
*Taking you pulse ensures you are not working too hard.
How to Calculate Your Target Heart Rate
A common method used to calculate target heart rate is:
Maximum heart rate is 220 - age. It is generally recommended to aim for at least 60% of maximum heart rate during aerobic exercise, although people who have been inactive shoulder start out with a lower intensity and gradually increase intensity over time.
Note: Measuring intensity by taking your pulse is not always accurate, e.g. certain medications lower the heart rate and the heart rate in water is slower.
Note: Judging intensity by the way you feel or by your heart rate both measure Relative Intensity. How hard your heart has to work during a specific aerobic activity is relative to your level of fitness. What starts off as moderate-intensity activity may become light-intensity as fitness improves. As your cardiorespiratory fitness improves, you will have to work a little harder to get your heart rate up.
The following heart rate chart is a general guideline only, based on average maximum heart rates according to age.
Heart Rate Chart
*Fitness must be built up gradually. Doing too much too soon can result in "overtraining". Overtraining (exceeding the body's ability to fully recover between workouts) depresses the immune system and can cause insomnia, lack of energy, low mood.
NOTE: People with chronic health conditions (e.g. heart disease) should consult a physician before doing vigorous-intensity aerobic physical activity. Men over the age of 40 and women over the age of 50 should check with their physician before doing vigorous aerobic activity to check for hidden heart disease.