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High Intensity Cardio

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The Benefits of High Intensity Cardio

By Dr. Kristie

For years fitness experts expounded the virtues of doing thirty minutes to sixty minutes of cardiovascular exercise at the pace of a brisk walk or a slow, steady jog.

But recently, attention has turned to doing shorter, more intense cardiovascular exercise designed to boost the heart rate into the zone where you’re breathing hard and sweating buckets. Are intense cardio workouts really better than slow and steady?

How Are Intense Cardiovascular Workouts Different?

When you work out at a moderate intensity, like walking briskly or running at a steady pace for longer periods of time, you’re primarily activating muscle fibers called type 1 or slow-twitch muscle fibers. These muscle fibers are designed for endurance exercise of longer duration.

On the other hand, when you pick up the pace and work out at an intensity where you can’t string together a full sentence you’re breathing so hard, you activate a second type of muscle fiber called fast-twitch muscle fibers.

These fibers are designed for strength building and higher intensity exercise. These are the muscles sprinters use when they take off across a field.

Interestingly, long distance runners who maintain a slower, more sustained pace for longer periods of time have a higher percentage of body fat than sprinters even though they look thinner. Sprinters look lean, but they have more developed musculature, because they use more fast-twitch muscle fibers.

When you pick up the pace by doing high-intensity cardio, you not only activate more muscle fibers, but more fast-twitch muscles, which give a greater calorie burn.

Even though percentage-wise you’re using less fat as fuel and more carbohydrates at these higher intensities, you’re burning more total calories, which add up greater overall fat burning - just like the lean, muscular sprinter.

Another Advantage of Intense Cardio Workouts

Not only do you activate more muscle fibers when you do intense cardiovascular exercise, you also benefit from the greater hormonal response.

Intense exercise causes greater release of epinephrine, norepinephrine and growth hormone, which helps to burn fat even after you’ve recovered from a session of high-intensity cardio – and you’ll continue to burn calories for several hours afterwards. An intense cardio workout is the ultimate metabolism booster.

The Bottom Line?

If you enjoy slow, distance running, don’t give it up, but do at least two ten sessions of intense cardio each week to “shock” your body, activate fat-burning hormones and add variety to your workout – or try interval training where you alternate one minute of low-intensity exercise with a sixty seconds of intense cardio for twenty minutes.

This is a great way to break out of a plateau. But always check with your doctor before doing high-intensity cardiovascular training especially if you have heart disease or hypertension.

About the Author

She is a Medical Doctor with a concentration in Family Practice. She also has an undergraduate degree in both Biology and Psychology and masters in Clinical Pathology.


  • Exercise Physiology. Seventh Edition. Power and Howley. 2009.


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