Definition: The term intensity refers to how hard you're working during you're workout. Intensity is one of the most important
components of your workout program. When you workout at a sufficient intensity, your body grows stronger and you'll see changes in your weight, body fat percentage, endurance and strength.
For cardio workouts, you can use the talk test, your target heart rate and/or perceived exertion to monitor your intensity.
For strength training, the measure of your intensity includes how much weight you lift, how many reps you complete and how long your workout session is.