The Cardio Myth

I have recently introduced you to the book Body by Science by Doug McDuff, MD and John Little. This book offers a clear explanation of the actual science of exercise, how activity relates to hormones, and how this determines what happens in your body. In short, it answers the question I am frequently asked. “Why am I gaining weight when I am working out every day?”

In the introductory article I summarized his key points. In this article I will address one of those key points. His recommended method of exercise is what he terms high intensity training (or HIT). It benefits both the aerobic and anaerobic energy pathways. Most “cardio” only works the aerobic pathway.

High intensity training is in many ways the complete opposite of what is now known as “cardio.” HIT is designed to be short and sweet. The techniques work the major muscle groups to exhaustion and then you must stop, rest, and then begin the next exercise. Cardio is designed to be lower intensity so that you can perform the exercise without stopping, usually anywhere from 45 minutes to an hour.

The roots of modern cardio trace back to the mid-1960’s when Kenneth Cooper was searching for an exercise that he thought would optimize cardiovascular fitness. This was the time when we first began to see a dramatic increase in heart disease related deaths and the thinking was by exercising our hearts they would not attack us!

Unfortunately he began with a false premise. He believed that “aerobic” was the same as “cardiovascular” and wanted to develop an exercise that would isolate the aerobic metabolic system. He created the term “aerobics” to refer to his exercise technique. This low intensity and steady in state method he developed is now referred to as “cardio.”

But this is where we have to understand how the body works! The body has two pathways for metabolism – aerobic and anaerobic. These processes are conducted in each and every cell in our body. Both are essential for the total health of the cell and thus the entire organism. Aerobic means “with oxygen” and anaerobic means “without oxygen.”

Cooper believed that the aerobic was the most important pathway therefore it should be isolated and trained. There was no actual evidence that one pathway was more important, it was just his belief, and unfortunately for many he was wrong. For many it proved to be dead wrong.

His main error was that the pathways cannot be separated in a live human (remember our body is not a test tube – what happens in the body is different than isolating something in a test tube!). The aerobic pathway is fueled by a substance called pyruvate which is produced by the anaerobic pathway.

As we’ve discussed before energy comes from glucose going from the blood stream into the cell. It takes a series of twenty chemical reactions to produce pyruvate from glucose. This is an anaerobic process. Pyruvate then goes to the mitochondria of the cell. If you remember your basic biology the mitochondria produces energy via the Krebs cycle in an aerobic process.

So, as you can see, we need an exercise method that will strengthen both systems of metabolism. Modern day “cardio” does not fit the bill as it isolates the aerobic and the science share in the book shows it does not benefit the anaerobic. It is high intensity training that will benefit the complete system.

The effectiveness of any exercise is all about hormones, fat metabolism, and blood glucose levels. High intensity training works the major muscle groups to exhaustion, uses up glucose, and encourages the body to burn fat and build muscle. This is explored further in the article Hormonal Implications of Exercise.

Another irony concerning aerobic specific training is that it produces additional oxidative stress on the body which creates inflammation and excess free radicals in the body. This factor puts one at increased risk of heart disease – exactly what the “cardio” exercise is supposed to help prevent!

Bernard Rosen, PhD is a Nutrition Consultant and Educator. He works with individuals, groups, and at corporations to create individualized nutrition and wellness programs. His office is in Mequon, WI. To learn more or to schedule an appointment, e-mail at, call (262) 389-9907 or go to

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