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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Comments

  1. Marylyn Barber says:

    I am a Fitbit fanatic, I wear my Fitbit Flex everyday but I’ve learned not to rely on their numbers. I like my Fitbit because it reminds me to get up and move around especially when I’m at work.

    • Karen Stefaniak says:

      I think that is exactly what they are good for. Many people have had success wearing them. It’s the calorie’s spent part of it that troubles me. Keep on keeping on, Marylyn. You’re doing great!!

  2. Marylyyn says:

    Thanks Karen! I definitely don’t believe everything the Fitbit says because there’s flaws in these fancy gadgets. It’s also a great conversation piece…I was talking to a insurance rep this week and we both had on our Fitbit Flex and we spend at least five minutes talking about it. Also, these new fitness gadgets you can link them to other sights like mynetdiary or myfitnesspal. I use Earndit to accumulate points, which you can use to purchase items like workout clothing, fitness gadgets, energy bars etc, I don’t get hung up on the numbers, I’m more concerned if I don’t make it to step class, now that’s where it counts!!

    • Karen Stefaniak says:

      How fun that you can connect to win stuff! I’m going to have to look into that!!