Wednesday, May 18, 2011

Calculating Calories Burned Based on Average Heart Rate

I got at least a little intrigued by this idea, and have started doing my traditional poke around the internet. here's what I've come up with so far:

All look pretty similar. What I'm going to do is to enter the information from my workout last night into each and see what they come up with. Here's the info from last night:

Avg Heart Rate: 141 BPM
Duration: 57:00 min

And my info...

29 years old
235 pounds
45 VO2 Max

Here goes:

Triathlottrainingblog says: 840 calories burned
Shapesense says: 895 calories burned
Braydenwm says: 841 calories burned

There are some other factors, of course. These calculations are based on a heart rate between 90 and 150 BPM. If you go above or below those, the calculations are no longer accurate. I'm also thinking there has to be an element of heart rate zones in here somewhere. I know you keep burning calories all the way into your Zone 5, but the calories are now predominantly glycogen instead of stored fat.

Since this is as good a time as any to get into a discussion of heart rate zones, let's get to it. You can do all of this with calculations which are really just estimates based on age and gender, without any real bearing on what your own numbers might be. That is why science invented the stress test, to see what your very own heart and lungs can do. I'm thinking more and more that I should get one of those. Until I do, though, here's the info I've been able to scrounge up.

I just found this article and I like what it has to say.

Your maximum heart rate is 220 - your age according to most sources. So for me, since I'm 29, my maximum heart rate is 191. Seem arbitrary? It is! By this logic, a 29 year old marathon runner has the same heart rate as a 29 year old quadriplegic who runs zero marathons. Silly, obviously.The one in the article is at least slightly better, hopefully. It's 210-(50%*Age) - (5%*Weight) + 4 for men and 210 - (50% * Age) - (1% * body weight) for women. Using that calculation, mine is 188. It still doesn't have anything to do with my fitness, but at least now it's tied to my body in some way.

Your resting heart rate is your heart rate when you're totally at rest. The best way to calculate this is to take your pulse a few days in a row before you get out of bed. I'm sort of miserable at doing this. I suck at counting my own pulse, and I really suck at remembering to do anything before I get out of bed. I'm going to guess my resting heart rate is 60 and try very hard to remember to measure it over the next few days.

Your "Heart Rate Reserve" is the difference between your resting heart rate and your max. Think of it as the heart rate you have left over between complete rest and maximum work. So you take your max HR (191) and subtract your resting HR (60) to get your HRR (131).

Let's talk about zones. Zones are broken down by percentages of max HR, generally. One of the sources I found breaks them down by percentage of HRR + Resting HR, but that's the only one I can find that does that, so it may be a bunch of hooey. I think the % of Max HR is the way to go, just based on the numbers you get. Using the more complicated method indicates that you're not even starting to get into a training zone until you get up to 124 BPM, which seems really silly.

Zone 1 is your heart fitness zone. It's a brisk walk. You're not really burning fat or increasing cardio capacity, but your heart is moving and you're getting the benefits of low-intensity exercise. This is 50%-60% of your Max HR, or 94-112 for me.

Zone 2 is your fat burning zone. It's a low enough intensity that you can stick with it for a good long while, and you're burning up to 85% of your calories from stored fat. This is a good place to be. Most people (myself included) tend to train too hard and miss this sweet spot. This is 60%-70% of your Max HR, or 113-130 for me.

Zone 3 is the aerobic zone. This is your cardio training zone. You're burning about 50/50 for carbs and fats, so it isn't the most efficient zone for fat burning, but it the best place to be to increase your overall cardiovascular health. Your heart and lungs are working hard in this zone, meaning you'll be increasing their capacity to do work. This is 70%-80% of your Max HR, or 131-149 for me.

Zone 4 is the anaerobic threshold zone. This is where your body can no longer supply your muscles with enough blood and oxygen to keep them operating in an aerobic mode, and has to switch to anaerobic to keep going. You're not using very much fat at all for energy at this point. You're switching over to using primarily glycogen. Training in this zone will help you to increase your threshold, meaning you'll be able to work harder without getting into this zone. You can only work in this zone for so long before you deplete your glycogen stores and you fatigue. Depleting your glycogen stores means your body builds them back even larger, so this is also where you train to increase your glycogen capacity. This is 80%-90% of your Max HR, or 150-168 for me.

Zone 5 is your maximum heart rate, or your "Red Line" zone. You can't work in this zone for more than a couple of minutes at a time. This is where you throw up, pass out, injure yourself, etc. It's not a place to spend long periods of time. It's useful to train here, because this is where you can increase your speed. People normally train in this zone using intervals. This is 90%-100% of your Max HR, or 169-188 for me.

Now that we've gone through all those, here's the kicker: Each zone will not be a simple 10% swath of your heart rate. Depending on how you've trained, certain zones will be wider or narrower than others. If you've trained in sprinting a great deal, your AT (anaerobic threshold) may be very high. That would mean your Zones 4 and 5 would be compressed, and your Zone 3 might be extended. If you never work your AT, your Zones 1-3 might be compressed due to a significantly lower AT. Individual zones could be larger or smaller and none of these calculations have any way to account for that. They're estimates at best, and they're really estimates based on estimates based on averages. So...nearly worthless. But maybe, just maybe, you will have your actual zone limits close enough to where your estimated zone limits are that when you train intentionally in the middle of Zone 3, you will actually be working your own personal body in Zone 3. So...there's that. The bright side is that anything under Zone 4 will burn fat, just not as efficiently as being in Zone 2. Anything above Zone 2 will help increase cardio capacity, just not as efficiently as Zone 3. So there's a range available, it's just not something where you can say "Hey, it's fat-burning day. Let me take these numbers I calculated from the internet and do my workout in Zone 2," and be anything more than kinda sure that you're actually doing that. You'll still get benefits of course, they just may not be the benefits you're looking for. Since I'm currently at a point where literally any improvement in any area of health or fitness is a worthy goal, I don't have to worry too much about it. But I probably will anyway.

Thanks for reading!

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