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The Reality Of Aerboic Exercise Having Little Impact On Metabolism

Fitness myths and misconceptions, ah yes one of my favorite subjects to discuss. I think it’s the coach in me as I hate to see people trying really hard to meet their fitness or weight loss goals only to spin their wheels with ineffective programming.

Without question, one of the biggest areas of misconception is that aerobic exercise is the KEY to losing weight…and the more of it the better.

In today’s post I’m going to address this whole idea of aerobic exercise increasing your metabolism. Actually I’ll be doing more explaining on how aerobic exercise doesn’t really do much to increase metabolism.

A lot of people are fixated on the number of calories that are burned during a workout, the duration, and how much they sweat. The reality is they should be more concerned with how the workout impacted metabolic processes.

Exercise that has the GREATEST impact on changing body composition contains the following criteria:

1. the activity creates a metabolic disturbance by stimulating the central nervous system

2. the activity produces a hormonal response from the adrenal glands

3. the activity worked large muscle groups with an overload stimulus

This is one of the main reasons why new research continues to show that high intensity resistance training and interval training (aka. burst training) have the most impact on metabolic rate, hormonal response, and body composition change.

But let’s get back to aerobic exercise (aka traditional cardio).

When a lot of individuals set out on a weight loss program they’ll factor in exercise with aerobic or cardiovascular based training. I guess it’s because there’s still this misconception that cardio is for fat burning and weight training is for muscle building.

Like you simply plug in one or the other depending on your fitness goals. As you may be able to attest to, the fact of the matter is it’s not that simple.

I think a big reason for this misconception is that when people change their diet and start doing aerobic exercise at the same time (walking, elliptical, stationary bike, etc) AND then begin seeing the scale go down, they think…

“Wow, that <fill in the blank exercise> must be working.”

When in reality what’s really working is the changes in your diet.

Sure, the aerobic exercise assists with the process and leads to a healthier body, but it’s not the driving force behind the weight loss.

The research confirms what scores of people find out in frustration in the real world. It’s DIET….DIET…DIET!

Exercise is certainly important, but not in ways you might think.

Consider some of the following research studies:

Three Month Study

The addition of 45 minutes of aerobic exercise at 78% Max Heart Rate (MHR) for 5 days a week over 12 weeks.

Result: The inclusion of the above exercise protocol (albeit 5 days a week!) had no effect on body composition over dieting alone.

Utter et al.
International Journal of Sports Nutrition 1998 Sep;8(3):2

Six Month Study

Two groups were divided with one being “diet only” and the other “diet plus aerobic exercise.” The group that included aerobic exercise did 50 minutes – 5  times per week.

Results: The group that included aerobic exercise saw no additional impact on body composition over the group that used diet only.

Redman et al
The Journal of Clinical Endocrinology & Metabolism 2007-Jan

And to really put the exclamation point on the fact that diet is the single largest factor, consider the following:

Twelve Month Study

A group of overweight men and women were tracked for an entire year to see the impact on aerobic exercise with their weight loss. They were NOT instructed to make any specific changes to their diet. The exercise protocol was 60 minutes of low-moderate intensity aerobic exercise completed 6 days per week.

Result: Average weight loss after one year was 3.5 lbs or about 0.3 lbs per month. The average was 3.08 lbs for women and 3.96 lbs for men.

McTiernan et al
Obesity 2007 June – 15:1496-1512

This was after an entire year of doing hour long aerobic workouts, 6 days a week! All for a measly 3 lbs of weight loss. Talk about a letdown. No wonder so many people give up on a weight loss program when their exercise isn’t working.

I’ve said it before and I’ll say it again….”you can’t out-exercise a bad diet.”

What would have been interesting to see was the comparison of two groups, with one making changes in their diet and the other not. Still using the same exercise protocol.

I have no doubts the aerobic exercise plus diet group would have done far better with as much expenditure they had with the workouts (60 minutes- 6 days per week).

But even still, the reality is they could see even better results by changing the nature of the exercise. You don’t need to exercise for an hour a day, six days per week. For a lot of individuals this isn’t conducive or even doable due to work and other responsibilities.

One of the primary reasons we don’t see aerobic exercise having much of an impact on body composition is because it has little impact on metabolism.

It’s easy to get caught up in the “calories burned” trap and miss the bigger picture. The ability of exercise to change body composition goes far beyond a a simple “calories in versus calories out equation.”

There is this general belief that exercise is beneficial for weight loss because it helps increase your metabolism (or the rate in which calories are burned).

The truth is not all exercise has much of an impact on metabolic rate.  The reason that aerobic exercise has a minute impact on metabolism is because there’s little metabolic disturbance or hormonal response.

In other words, when the exercise is over so is the increased rate of energy expenditure.

There is something in exercise science called “EPOC” or (excess post exercise oxygen consumption). While this is a heavily debated subject (and full of misconceptions of it’s own), the idea is that there’s a measurably increased rate of oxygen uptake following strenuous activity.

Without going into an entire dissertation on EPOC, a subject for another day, for simplicity purposes just know that low-intensity aerobic exercise has minimal impacts on EPOC while high intensity exercise has greater impact on EPOC.

The higher the EPOC, the greater the impact on body composition changes.

Case in point…Consider the following study conducted in 2001 by the Department of Physical Education, Exercise, and Sports Sciences at East Tennessee State University.

Individuals were divided into (2) groups. Both groups trained 3 times per week and completed the necessary exercise duration to burn 300 calories per workout. The training was completed over 8 weeks.

Group one did high-intensity, short-duration interval training, and group two did steady state aerobic training. The steady state aerobic exercise group did longer duration workouts because the lower intensity took longer to complete 300 calories of energy expenditure.

Result: The interval training group showed a -4.4% change in body fat whereas the low intensity steady state group exhibited a +1.2% change in body fat.

King et al.
A Comparison of the Effects of Interval Training vs. Continuous Training on Weight Loss and Body Composition in Obese Pre-Menopausal Women.

In another study, two groups trained 3 times per week for six weeks. The interval training group completed 4-6 intervals of 30 seconds on (high intensity), 4 minutes off (recovery).

The steady state aerobic group completed 30-60 minutes of continuous exercise at 65% VO2 max.

Result: Fat loss was 114% more with the interval training group than the steady state group.

Macpherson et al.
Run Sprint Interval Training Improves Aerobic Performance but Not Max Cardiac Output.
Medicine & Science in Sports & Exercise – 2010

So where does all this research leave us?

Just to be perfectly clear, I’m not of the assertion that aerobic exercise is completely worthless and serves no beneficial role in a body transformation program. I believe that is does, just not to the degree that many people think.

If I were to give you a hierarchy of importance for body composition change it would look something like this.

1. Supportive nutrition (once again diet tops the list)

2. Activities that burn calories, promote lean muscle mass development, and elevate metabolism (high intensity resistance training…aka burst training).

3. Activities that burn calories and elevate metabolism (high intensity interval training – cardio).

4. Activities that burn calories but don’t necessarily maintain lean muscle mass or elevate metabolism (aerobic based exercise).

So it’s not that aerobic exercise isn’t included in the list, it’s just the last item in terms of importance. All things being equal and I’ve only got “X” number of hours to exercise during the week, I’m going to recommend you plan your time accordingly.

Focus your time on the activities that have the most impact on body composition changes (the old 80/20 rule). If you’ve got time to complete additional aerobic exercise, great, by all means include it. Just don’t put it at the top of your priority list.

A lot of fitness gurus make the assertion that metabolic resistance training and interval training is the ONLY way to go for fat loss. While there’s an argument to be made that these are the more effective forms of exercise for fat loss, it doesn’t mean they’re the only way.

Truth be told you could make a significant impact on body composition change with a combination or resistance (weight training) and several bouts of aerobic exercise each week. You’d have to spend more time with the aerobic exercise but it would certainly work.

The sweet spot as I see it is the combination of ALL of the above. There’s a lot to be said about variety with an exercise program. The more you work all the energy systems of the human body, the better the results.

There is simply no holy grail of exercise for fat loss. As much as I endorse burst training and interval training, you couldn’t do it ALL of the time.

For starters, recovery would be a major factor. High intensity training is very taxing on the body and couldn’t be completed on a daily basis. You could try but the intensity would invariably go down over time, if you didn’t wind up injured or burned out first.

There’s no benefit of keeping the pedal to the floor all the time. In my experience the most effective exercise programming combines a little bit of everything.

Burst training (2-3 times per week) for resistance work, and cardio based work with a mix of interval training and low-moderate intensity aerobic exercise.

The idea is to factor in the above in a way that fits with an individual’s schedule, time availability, and takes into consideration sufficient recovery.

Once again, priority is placed on the activities that have the greatest impact on metabolism and body composition change.

If there’s one big take-a-way from all of this it’s that aerobic exercise isn’t the magic bullet for weight loss that many individuals mistakenly believe it to be.

It’s a great place to start, after all you can’t come out of the gate doing high-intensity exercise. The point is all that walking or time on the elliptical or stationary bike won’t do much unless it’s combined with resistance training and dietary changes.

Invariably there will be someone who reads this and says…yeah but, I know someone who didn’t change their diet much at all and started running every day and lost a bunch of weight, etc.

Remember not everyone has the same genetics, metabolism, and bioindividuality. There are those lucky few in the minority with a fast metabolism, high insulin sensitivity, and good genetics that can burn off fat with lots of physical activity (albeit any physical activity).

This doesn’t mean it will work for everyone obviously. While you can’t control your genetics, you can elect to exercise in a way that will have the most significant impact on metabolism.

In general, if the exercise is always “easy” it won’t be doing much in the long run to help you see a significant change in body composition. The human body adapts when an overload stimulus is provided.

In other words, “hard work” will be required. Deep down in your heart, I’m sure you already knew that.

Shane Doll is a certified personal trainer, fat loss expert, speaker, and founder of Shaping Concepts Fitness Training Studios. If you’re looking for a personal trainer in Charleston, you can receive a no-obligations personal training trial and consultation without risking a dime. Over 1000 Charleston area residents have transformed their bodies following our unique burst training workouts and simplified nutrition programs. Experience the Shaping Concepts difference today.

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Category: Fitness Training.