Intensity is a word that is used to describe how hard you are working at an activity. The easiest way to figure out how hard you are working is to use a scale of 0 to 10, where sitting or doing nothing is a 0 and the highest level of activity or the hardest you could work is a 10. That makes a 5 or 6 something right in between really hard and really easy and is considered moderate. At that level you should be breathing a little bit harder than normal and your heart should be beating a little bit faster than normal. If you get to a point that seems like your heart is beating much faster and you are breathing much faster than normal, then you are probably doing vigorous activity or would choose a 7 or 8 on the scale. Remember at the beginning when we talked about the recommendations? You should do moderate activity for 60 minutes every day. You should also try to do vigorous activity 3 times per week. Now that you know the scale, you’ll know how hard you’re working and can make sure you get all of the activity in each day that you need! 
One definition of intensity is the degree of resistance, energy or difficulty as related to a workout. There are several ways to assess the intensity level at which you are working. The first is to know your target heart rate and find your training zone. This technique was discussed in the last tip. The goal of using your training zone is to work at a level that is 60% to 80% of your target heart rate. It is an objective measurement of how hard you are working when doing exercise. This method is extremely useful and will give you a good idea of the intensity level you are achieving during your work-out. The down side of this method is that some medications and other factors can change how your heart rate reacts to exercise. For example, if you take beta-blockers, they actually make your heart rate stay lower during exercise. If you are trying to reach 60% of your target heart rate, you may be working harder than you think and might even reach an unsafe level. Another way to gauge how hard you are working is to use the Rate of Perceived Exertion scale. To use this scale you choose how hard you are working on a scale of 6 to 20. Although it is a more subjective measurement, it is extremely useful during exercise because it is quick and does not require the skill of taking a pulse or calculating the figures associated with the target heart rate training zone. It is also useful for those people who have heart rates that might respond differently to exercise.
The scale looks like this:
6
7 extremely light
8
9 very light
10
11 light
12
13 somewhat hard
14
15 hard
16
17 very hard
18
19 extremely hard
20 maximal exertion
Koosh Ball