Do You Really Know How Many Calories You Burned In That Work Out?

Most of the nifty fitness trackers let you to add the calories that you burn during workouts back into your daily calorie allotment which can lead to weight loss sabotage. Unless you know what your basal metabolic rate (BMR) is you can’t know how many calories you’re burning at rest or at play.

Getting an accurate  BMR measurement isn’t easy. To accurately calculate your BMR you will need to undergo an indirect calorimetry test which means you’re hooked up to a machine that measures the volume of oxygen consumption and the volume of carbon dioxide output.  The test is done in a lab or clinic where they have the equipment to properly administer the test.

Since it’s not possible for most people to get their BMR measured in this way they do the next best thing.  They use an on-line calculator that has them enter height, weight, age, gender and activity level. The web page then calculates your BMR and provides you with the number of daily calories you need to consume.

BMR 2

On-line BMR calculations are a guesstimate at best. In fact, The American Council on Exercise says these calculators can be off by as many as 1,000 calories!

Most People Overestimate Calories Burned During A Work Out

Where people get into trouble with calculating calories burned during exercise is it’s difficult to properly estimate activity level. Most of us think we’re working harder than we actually are which means we think we’ve burned more calories than we have. This was the focus of a study being done by a team of researchers at the University of Ottawa.

At the U of O, researchers had a small group of participants take a brisk walk on a treadmill until they were told to stop. They were then led to a buffet table where they were instructed to consume foods that would equal the calories they spent in their workout. Not surprisingly, the group consumed two to three times more calories than they had burned on the treadmill.

A follow-up study in the UK had participants exercise at 60 to 90 percent of their V02 max.  They maintained that intensity until they had burned 450 calories or a treadmill. As in the Ottawa study they were then led to a buffet and were told to match the number of calories that they ate to the amount they burned on the treadmill.

The results were similar to the first group however this group underestimated the number of calories they burned. That did not stop them from overeating. They overate to the same extent as the people in the Ottawa study did.

What This Means For You

I’m not anti Fitbit, Jawbone or MyFitnessPal. I think they are all excellent ways to track calories and activity and keep you motivated.  But I worry that too many people are relying on these devices and apps to accurately tell them how many calories they’ve burned doing a workout. Then they think it’s okay to put those calories – or more according to the studies – back in to make up for the loss.

Fitbit calories burned

Flickr photo by Nagu Tran

Your Fitbit cannot possibly know how many calories you’ve burned on a four mile run.  It can tell you how much the average person of your height, weight and gender might burn. But it can’t tell you how many you’ve spent.

Go ahead and track your calorie intake and do your daily workouts but don’t add back the calories you’ve burned working out. Let those goes. Think of it as a bonus then see if you have more success reaching your weight loss goal.

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Beware of Fitness Instructors That Tell You You’re Torching 800 to 1,000 Calories.

They may not be telling  you the whole truth.

I received an e-mail today with an article attached and a question about calorie expenditure during exercise.  The article listed a variety of workouts and stated how many calories would be burned  per hour for each one.  Here’s what it said:

  • Kickboxing – 800
  • Spinning – 700
  • Zumba – 500
  • Jump Rope – 780
  • Step Aerobics – 600
  • Running – 650

Figuring out how many calories you burn during exercise is tricky because everyone is going to burn a different amount.  I couldn’t tell you which participant these estimates are based one, but I do know that I’ve never come close to burning 500 calories in Zumba.

Which one torched 1,000 calories in Spin class?

Which one torched 1,000 calories in Spin class?

Your Metabolic Fingerprint

The number of calories you burn in a normal day is determined by your Basal Metabolic Rate (BMR).  It is as individual as your fingerprint and is influenced by a number of factors including your body size, body composition, gender, and age.

Accurately determining your BMR can be done with a breath test.  There are also many on-line calculators that will give you an idea of what your BMR is, but remember, those are only estimates and if you’re trying to achieve an exact calorie-in-calorie-out balance you don’t want to rely on them.

How You Burn Calories When You Exercise

In a Spinning class with 25 people on 25 bikes each person will burn calories a little differently based on their BMR and the intensity that they are exercising.  The number of calories they burn in that hour is determined by how much oxygen they are using, in other words, their heart rate.

Your Maximum Heart Rate (MHR) is about 220 heartbeats per minute minus your age although, an older physically fit person can achieve a higher MHR than someone younger who is out-of-shape.

To improve cardiovascular endurance and burn the most calories, your target heart rate zone when exercising should be between 80 and 90% of maximum.  So, theoretically a 32 year old working at 80% MHR would be at 150 beats per minute.  But, let’s say everyone in the Spin class is 32 years of age.  Not everyone would be at 80% of their MHR if they counted their pulse and found their heart was beating at 150 BPM.

This is one reason why the Target Heart Rate Chart, that at one time was on the wall of every fitness class studio in the world, has been replaced by a chart that allows the participant to measure Perceived Exertion.  Perceived exertion asks you to determine, on a scale from one to ten, how hard are you working?  If you’re at 10 you may need to slow it down.  If you’re at two you need to pick up the pace if you plan on burning any calories to speak of.

Getting an estimate of your BMR, taking your heart rate during class or while you’re on the treadmill, and measuring perceived exertion are all worthwhile.  But it’s important to keep in mind that all of these are estimates.  To know exactly how many calories you burn during a 60 minute Turbo Kick class would require you to be hooked up to equipment that measures your VO2 max.  That doesn’t sound like much fun.

Less is More

The danger in over-estimating calorie expenditure – which is what I think some fitness instructors do to sell the class – is that you leave thinking you’ve created an 800 calorie deficit.  To some of us that means we have an 800 calorie hole that needs to be filled.  With food.  If, in fact, you’ve only burned 400 calories but eat 800, you’ve got a problem and a new question: “Why do I gain weight when I exercise?”

The old rules of exertion still apply.  Whatever it is you do, do it consistently and work hard enough at it that you can’t carry on a conversation with you neighbor, but not so hard that you’re completely exhausted when you’re done. Find that happy place where you leave the class thinking you had a good workout and are anxious to come back for more.

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