How to Measure Intensity
1. Monitor your heart rate. This is best done with a heart rate monitor. Remember your maximum heart rate is your age subtracted from 220. Unless you are a beginner, you should shoot to work at 70% of your MHR or higher.
2. The talk test. If you can easily carry on a conversation with a friend while working out, you may be taking it too easy. However, during the last marathon I ran, I noticed two women in front of me gabbing away for several miles while I was dying trying to keep up with them. I guess there's always an exception.
3. The perceived exertion scale. This is a very simplified way to determine intensity. There are many variations of the scale and it's not as objective as measuring your heart rate, but I kind of like the simplicity of using the 0-10 scale of 0 being totally relaxed and at ease and 10 being I am going to die!
2. Work out with or in front of others. You are less likely to take 3 minute breaks between sets and loaf around during exercise if others are watching you work out.
3. Choose more intense activities and exercises. Rather than just walking or jogging, you may want to try sprinting. This is a very intense activity that will use all of your muscles. You may also want to try plyometrics or full court basketball instead of half court games or swimming laps instead of water aerobics.
4. Keep track of your personal best records. Know your personal best as it relates to push ups, pull ups, crunches,1 mile run, 1 rep max, etc. Having a prior record to occasionally work towards beating can be very motivating.
One of the benefits of the CrossFit movement is that it really increases intensity by incorporating several of these concepts. High Intensity training has several advantages over steady state exercise. I still think activities like jogging and walking are beneficial, but if you are looking to take things to the next level then you may want to re-evaluate the intensity level of your workout.
One word of warning. Exercising with intense ballistic movements is more likely to cause injury, so make sure that you have prepared your body for intense activities by slowly building up a foundation of strength training over time and make sure that you are sufficiently warmed up before you engage in intense exercise.