There is no real reason to constantly monitor your heart rate during your training unless you have a medical condition.

No, not really, heart rate training is overrated.

Several years ago, when I worked at a certain Big Box gym, I sold heart rate zone testing.  This was a test that a participant could do with us on a bike or a treadmill, where they ride or walk/jog faster and faster with a mask on their face. This special mask measured the carbon dioxide: oxygen ratio expelled by the person, sent it for analysis on a computer; and with that info coupled with their heart rate, we could tell how much fat they burned in real-time.

The idea was that we could tell the person which heart rates they should aim for to maximize their fat burn during future workouts.

It takes calories (energy) for the body to stay alive. It takes energy to keep the brain functioning, heart beating, and basically just to keep the lights on. And the human body uses a mixture of calories from fat stores and sugar (glycogen) stores for that energy. To use the fat for fuel, body has to have plenty of oxygen. At lower heart rates, even while sitting here reading this right now, your body is probably burning mostly fat, although only a few calories. This is called being “aerobic,” and it usually happens up to about 60% of your maximum heart rate.

When you workout and your heart rate goes up to 70-100% of your max heart rate, the body starts getting too little oxygen to be able to burn fat, so it switches over to the sugar stores. Sugar does not require oxygen to burn so it is used primarily when the body is “anaerobic.” At the highest heart rates, although you are burning more calories, very few of them come from fat.

Then there is the sweet spot:

Somewhere in the middle where the body is burning a high amount of calories due to a higher heart rate, but the heart rate is not so high that the body has switched over to burning sugar. This is the spot where people should strive to keep their workouts. By maximizing the fat burn, we are working smarter, but not necessarily harder. Even if weight loss is not the primary goal, burning fat stores will allow the body to work longer than burning through the sugar stores.

The test that I sold at the Big Box gym told us at which heart rates the individual person maximized their fat burning. We also told them they needed to come back in 3 months for re-testing because as they got fitter, their zones would shift.

Here’s the dirty little secret that even I didn’t know at the time:

Your heart rate zones don’t just shift after getting fitter 3 months later. They shift day to day.

How much rest you get, how much and how well you eat, your emotional state, hormone levels, and a myriad of other factors affect your zones. Which means that when you test your heart rate zones, they are only accurate for that day. The next day, they will likely shift.

Rate of Perceived Exertion Scale

There’s a better way than constantly monitor your heart rate during your training. It’s called the RPE scale or the Rate of Perceived Exertion Scale. Using a scale of 1-10 (10 being the hardest) you get to be the judge of how hard you are working out. A 10 will feel different to you based on the day you are trying to work out. If you had a tough night the night before, a 10 today might feel the way a 5 did yesterday. Or if you had a great night’s sleep and a healthy breakfast, maybe yesterday’s 9 feels like a 4 today. And that’s the beauty of this scale. You can adjust your workout to fit how you feel without a heart rate monitor or any fancy tests.

Ultimately, if your goal is fat loss, you should be trying to keep your workout at a moderate intensity for the majority of the workout. This should feel like a 5 or a 6 on your RPE scale, which means you can talk, but you couldn’t sing. That’s the sweet spot.

Final takeaway:

Unless you have a medical condition and your doctor has recommended working out below a certain heart rate, there is no real reason to constantly monitor your heart rate during your training. A better way to evaluate the effectiveness of your workout is to use the RPE scale and keep yourself at a moderate intensity.

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