You always need to be aware of your intensity level during a cardio workout. Getting into the aerobic zone is the key to both cardiovascular benefits and calorie burning. You will often hear about the "target zone" or "target heart rate"-this is a percentage increase over your normal pulse rate. To get a real cardio workout, you want to keep your pulse in the target zone for 20 minutes. A heart rate monitor you wear is the easiest way to keep track during your cardio workout.
Your personal target zone depends upon your age, weight, and fitness level, and can change over time. Once you know your target heart rate, during your cardio workout you should periodically check your pulse by using your index finger and middle finger to find the pulse below your ear behind your jaw. Count the number of beats for 10 seconds and multiply by six.
The other way of maintaining your cardio workout in the target zone is by using the scale of perceived exertion. The standard is the Borg Rating of Perceived Exertion. Essentially, you'll know when you're in your target zone when you are breaking a sweat and can tell you're working, but can still say at least 25 words without gasping for breath. You should be able to describe the exercise as "somewhat hard." If your cardio workout involves interval training, during a one-minute interval of intensity you should feel like you're working hard and would find it difficult to say more than a couple of words at one time.
The post-interval recuperation period during a cardio workout is at a level where you still break a light sweat but can talk comfortably.
