Cardio, Calories and Fat Burning
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Is Your Personal Trainer Current with the Latest Fitness Info?

Okay, in the spirit of full disclosure, I’m writing this blog post as a result of a conversation I heard  today between another trainer and their client. The trainer is a good trainer, but in my opinion – gave some outdated information and advice.

The Scenario

I overheard a discussion between a trainer and their client about burning fat calories while doing cardio.  In short, the client wants to lose weight and get the most out of her 20-minute cardio workout.  She was trying to figure out what her “fat burning zone” is based on her heart rate.  Also, she has a goal of burning 200 calories in 20 minutes.  The trainer gave her information that is outdated and proven to be wrong in recent reputable studies on the subject of cardio, calories and fat burning.  Here’s why.

Issue #1 – Target Heart Rate

Up until this past summer, women were lumped together with men when calculating targeted heart rate.  But a recent study of 5,500 women by Northwestern Medicine in Chicago has resulted in a new formula.  The New York Times article on the study was reported in July of 2010.

According to the study, a decades-old formula for calculating heart rate is largely inaccurate for women, resulting in a number that is too high.  The commonly used formula subtracts a person’s age from 220 (HRM = 220 – age).  This forumula is still considered to be okay for men.   But based on the data collected in the Chicago study, the right formula for calculating a woman’s maximum heart rate is a little more complicated: 206 minus 88 percent of a woman’s age.

Ladies’ HRM = 206 – (age x .88)

The article draws attention to the  fact that using the old formula of 220 minus age, a 40-year-old woman would achieve an average maximum heart rate of 180 beats per minute. That means her pulse should stay around 153 beats per minute during her workout to achieve a target heart rate of 85 percent. That would be considered a high-intensity workout.  A low-intensity workout would be 65%, or 117 beats per minute.

Using the new calculation, that woman’s average maximum heart rate is 171 beats per minute, meaning her desired target heart rate is just 145 beats per minute, 8 beats a minute slower than under the old formula.  The lower intensity workout would be around 111 beats per minute.  For a person who has developed good cardiovascular strength and endurance, this seemingly small gap can be a big difference between a strong workout and one that is too exhausting.

My Advice:Use the new formula, ladies.  But don’t get too hung up on occasionally reaching and passing your maximum heart rate – as long as your doctor is okay with it.

Issue #2 – You’ll burn more calories if you keep your heart rate at the lower end of your targeted heart range.

Not true.  What is true is that when a person is exercising at the lower end of their target heart rate, they’ll burn a higher PERCENTAGE of fat calories.  But, we know that to lose weight and burn fat, we have to create the biggest calorie deficit possible.  Let’s assume that you and I are the same age, weight and height.  If you go out and walk around your neighborhood for 30-minutes at a brisk pace, you’ll maybe burn 120 calories with 58 (48%) of those calories coming from fat.  While you are walking, I am running at a 10-minute mile pace.  I burn 325 calories with only 24% of the calories coming from fat.  I will have burned off 78 fat calories.  Remember, to lose weight, we must burn ALL calories.  Sure. you are burning off carbohydrates at higher intensities, but that’s what fuels our ability to crank through rigorous workouts and burn fat. Bottom line is, it’s all about the calories we burn and creating an energy imbalance and the body doesn’t care where those calories come from.

My advice:Up the intensity of cardio workouts by doing intervals and spiking that heart rate.  Use at 3:1, 2:1 or 1:1 ratio to go from easy to high-intensity.  On the treadmill, I will walk at 3.8 mph for two minutes and then run at 6.5 mph for two minutes, doing this for the entire 30 minutes.  My heart rate will fluctuate from 110 to 168.   Again, check with your doctor to figure out what is best for you in your current state of health.

Issue #3 – If your heart rate is maxed, you are only burning glycogen.

Well… sort of, but there’s more to it.  First, you are probably wondering, “What is glycogen?”  In simple terms, when we eat carbohydrates our body stores them for fuel (in the form of glycogen) to be used during activity.  It’s the gas in our gas tanks.  Once glycogen is used up for fuel, our body draws energy from our reserve gas tank which is full of nasty, yucky fat.   Our body reserves about enough glycogen for a moderate, 30-minute workout.  After 30 minutes, guess what happens? We start burning fat.  During a low intensity workout, our body will pass by most of the glycogen and burn a small amount of fat for fuel.  That’s why, in the example above, we burn a higher percentage of fat calories… but not MORE fat calories.

So, for the first 30-minutes we are on the elliptical or treadmill, we are primarily burning glycogen if we are at a low to moderate intensity.  If we continue for another 15 minutes, we then burn 15 minutes of fat stores for fuel because the glycogen has been depleted.  That’s one reason why doing 45- to 60-minutes of moderate cardio will burn more fat.  People who only do 30 minutes of low- to moderate-intensity cardio don’t see anywhere near the same weight loss results..

My Advice: There are ways around this dilemma.  First, know that strength training (lifting weights) zaps glycogen stores.  Glycogen is needed for the power to lift the weights and recover – it’s anaerobic.  That’s one reason that I recommend my clients do a 20- to 30-minute cardio session after lifting weights.  The fuel to complete the post-resistance training cardio session comes primarily from fat fuel.  If you do the cardio before you lift weights, then you deplete the glycogen stores that will give your muscles enough power to lift the weights.  The muscles don’t draw the fuel from fat for short bursts of energy.

Another solution is to exercise first thing in the morning before you eat.  You don’t have the glycogen stores available and you’ll tap into that reserve of fat fuel much faster.  But make sure to eat after exercise… replenish your carbs and protein.

What would I do?

So, what would I tell the other trainer’s client if I was her trainer?

  1. Let’s re-calculate your maximum heart rate and heart rate zone using the new formula.
  2. You can’t burn significant calories – especially fat calories – in just 20 minutes.  You won’t even get into burning fat with a moderate intensity workout.
  3. You need to increase your cardio workout to at least 45 minutes, three days a week.  You need to create a calorie deficit of 3,500 calories to lose one pound a week, 7,000 to lose two pounds.  You get that through cardio, strength training and sound nutrition (notice I didn’t say “diet”).
  4. You need to do intervals to take your heart rate up and improve your cardio endurance, especially if you can’t do more than 20 minutes of cardio.

If you are working with or looking for a personal trainer and want to be sure they are knowledgeable about current fitness issues, ask some questions like:

  • What is my targeted heart rate?
  • What is my targeted heart rate range for exercise?
  • Will I burn more fat calories during lower intensity or higher intensity exercise?
  • Should I do cardio or strength training first?
  • Is it okay to exercise above my maximum heart rate? If so, for how long?

If your trainer (or perspective trainer) can answer these questions, great!  If not, then find one who can.

To your health!

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