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Experts say you should do 30 minutes of cardio at a moderate intensity most days of the week. Sounds simple but what does moderate intensity really mean, and how do you know when you’ve reached that level?

Intensity may sound subjective, but it really is pretty precise. Here’s a primer on how to find your intensity level and how to make sure you are using that information to make it count for your health.

The goal of cardio is to push your body to keep the heart rate elevated for an extended period of time. This not only burns calories, but it strengthens your lungs, increases bone density, reduces your risk of cancer and heart disease, increases your energy and provides relief from depression and anxiety.

The key is to work hard enough to raise your heart rate to the level it takes to elicit change. This is called your Target Heart Rate, and this is completely individual.

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You can calculate your Target Heart Rate by subtracting your age from the number 220. This number is your Maximum Heart Rate. While exercising, you want to be working at 60-80 percent of your Maximum Heart Rate, so multiply your MHR by 0.6, 0.7 or 0.8. and that number is your THR. Working below your THR will not be effective and working above it can be dangerous. There are some exceptions to this, like if you have certain medical conditions, so always see your doctor before you embark on a fitness routine.

Wear a heart-rate monitor to track your heart rate during exercise, or simply stop and take your pulse in the middle of your workout to make sure you are working within your THR. Count your pulse for a full minute, as it will slow over that minute as you begin to recover.

For some, like beginners or the overweight, walking can be physically taxing enough to reach your Target Heart Rate. For others, you may find that you need to run. Swimming, cycling, dancing, climbing stairs or using cardio machines like an elliptical or recumbent bike are also great cardiovascular exercises.

As you become more fit, you will find you need a more challenging workout to reach your THR. Even if you are walking, challenge yourself. Mix some hills into your walk and keep the pace up. A leisurely walk, no matter your fitness level, isn’t going to cut it.

If the math is intimidating you, you can keep track at first, but eventually you will begin to learn what it feels like to work within your THR. You will also learn to love pushing yourself physically because when you do, you will start to see changes in your body. And those changes, inside and out, are what will keep you striving to work even harder.

Kelly Turner: Turner is an ACE (American Council on Exercise) certified personal trainer and fitness writer: On Twitter @KellyTurnerFit.

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