Why do I barely burn calories with cardio?

Question

Lately i have been doing a lot of cardio. I want to lose weight and I've been told that cardio burns a lot of calories. But about 2 weeks ago i bought a heart rate monitor (polar M400 HR). I have been wearing it during cardio - mainly during elliptical training and it says that i burn about 300 calories an hour. I expected way more to be honest. The calorie counter in my elleptical trainer says i burn about 600 though..

But what i was wondering: is the heart rate monitor always right? I am a young female with a normal weight, but yet I barely seem to burn calories even though I really train as hard as I can.

Answer 1

A heart monitor is only one data point or piece of the puzzle when it comes to calculating energy expenditure. Both the elliptical and heart monitor by themselves aren't going to be accurate, at least not in the sense you care about.

Typically, when you want to get a more accurate reading on calories burned, you need a device (fitness wearable, Fitbit, Garmin, etc.) that will accept several data points like: age, gender, weight, height, body fat percentage, etc. With this information along with your heart rate will you paint a more accurate expenditure of energy. Even with this information, it is still an estimate, but certainly better than a heart rate monitor or elliptical on its own.

For perspective think of this: you have two people that are 150 lbs, but one is 5'2" and the other is 6'0". Now put them both on the same exact program in an elliptical or recumbent bike. The net result is both of their calorie expenditures are going to be different. In this case, the 150 lb person at 5'2" will have burned more calories. They're overweight relative to their height and have to work harder to perform the same program as the 6'0" 150lb person.

One more thing to think about is your body adapts and becomes more efficient at performing the same exercises. For example, when you started running for 10 minutes, you might have burned 100 calories. After a month, and performing that same exercise at the same speed, you're now only expending 80 calories over 10 minutes. This can be further exacerbated by your diet if you're in a caloric deficit.

As a side note: if you want to burn fat and sculpt your body, lift weights. You burn more calories lifting weights than you do performing cardio. One exception is HIIT, or high-intensity interval training. It provides a similar effect that strength training provides, EPOC, or excess postexercise oxygen consumption. This is a fancy series of words for something known as the afterburn effect. Which means, you continue to burn calories 12-48 hours after the activity is over.

Why High-Intensity Interval Training Is Best For Weight Loss

Answer 2

I would look at the results of your heart rate monitor.

You may have been initially burning about 600 calories/hour on the elliptical, but repetition of the same workouts of the same intensity (and maybe even at the same time each day of the week) will allow your body to adjust and plateau. That's why so many people stress the importance of variance in your workouts. You might try the elliptical one day, rock climbing the next, and stair-climbing the day after! See if that seems to make anything different. Good luck!