Fat burn percentage Polar FT60

solevoix

I FINALLY just got a HRM - the Polar FT60. So far I love it, but I have a question about the fat burn percentage readings I'm getting. Yesterday, I took my dog for a long walk - very easy going (lots of pauses for sniffing, you know) with a few bursts of ball chasing/jogging, and in 90 minutes (69 of which I spent in "Zone 1") I burned 430 cals with 51% being fat calories. This morning, I did a 60 minute high intensity workout (57 mins in Zone 3) and burned 711 cals, but only 13% were fat calories. That percentage was much lower than I expected.

The argument I always hear people use is that, even though you burn a lower percentage of fat calories at higher intensity, you burn more calories overall so the number of fat calories will ultimately be higher as well. But that isn't the case in this example (219 fat cals in low-intensity workout vs. 92 fat cals in high-intensity workout). Of course I know afterburn is probably higher with the high intensity workout, but still.

I don't want to overanalyze - I'm just not sure what to make of these numbers. I'm looking to get leaner and drop about 10 pounds, so I don't know if I should worry too much about "fat burn", or just stick with the high-intensity and focus on getting a high calorie burn.

Azdak

I FINALLY just got a HRM - the Polar FT60. So far I love it, but I have a question about the fat burn percentage readings I'm getting. Yesterday, I took my dog for a long walk - very easy going (lots of pauses for sniffing, you know) with a few bursts of ball chasing/jogging, and in 90 minutes (69 of which I spent in "Zone 1") I burned 430 cals with 51% being fat calories. This morning, I did a 60 minute high intensity workout (57 mins in Zone 3) and burned 711 cals, but only 13% were fat calories. That percentage was much lower than I expected.

The argument I always hear people use is that, even though you burn a lower percentage of fat calories at higher intensity, you burn more calories overall so the number of fat calories will ultimately be higher as well. But that isn't the case in this example (219 fat cals in low-intensity workout vs. 92 fat cals in high-intensity workout). Of course I know afterburn is probably higher with the high intensity workout, but still.

I don't want to overanalyze - I'm just not sure what to make of these numbers. I'm looking to get leaner and drop about 10 pounds, so I don't know if I should worry too much about "fat burn", or just stick with the high-intensity and focus on getting a high calorie burn.

I'm terms of overall calorie burn, the FT60 has features that, if set up properly, make it a little more accurate than the lower-level Polar models. However, the % fat calories is just a gimmick. Even if it those numbers were accurate (which they most definitely are not), fat calories burned during exercise have NO effect on long-term fat loss.

vorgas

Bottom line up front: don't sweat it. Burning more is almost always better.

Now for the explanation:
When doing exercise like this, your body has two energy sources. One is to mix fat with oxygen (aerobic exercise). The other is to use the glycogen stored in your muscles (anaerobic exercise).

The fat burning process is relatively slow, and can't keep up when energy demands are high, so it turns to glycogen use.

When you're doing high intensity aerobics, some of the energy comes from the fat, some from the glycogen, right? The exact amount varies on the person. So lets look at your two workouts.

On day one you burned 430 calories, right? Lets say it's accurate and that 219 fat cals and 211 glycogen cals.
On day two you burned 711 calories. Again, assuming accuracy at 92 fat cals and 619 glycogen cals.

Now, your body is going to replace that glycogen. It's an imperative to it. Has to happen. The way it does that is with carbohydrates.

So lets say the next day you eat 175 grams of carbohydrates. That's 700 calories.
On workout day one, 489 of those calories will be converted into fat, because your glycogen stores are full.
On workout day two, only 81 calories will be converted into fat, because it takes a LOT more glycogen to replenish your stores.

So, over time, you will end up losing more fat with the higher energy workouts because you aren't gaining as much back. Make sense?

solevoix

Bottom line up front: don't sweat it. Burning more is almost always better.

Now for the explanation:
When doing exercise like this, your body has two energy sources. One is to mix fat with oxygen (aerobic exercise). The other is to use the glycogen stored in your muscles (anaerobic exercise).

The fat burning process is relatively slow, and can't keep up when energy demands are high, so it turns to glycogen use.

When you're doing high intensity aerobics, some of the energy comes from the fat, some from the glycogen, right? The exact amount varies on the person. So lets look at your two workouts.

On day one you burned 430 calories, right? Lets say it's accurate and that 219 fat cals and 211 glycogen cals.
On day two you burned 711 calories. Again, assuming accuracy at 92 fat cals and 619 glycogen cals.

Now, your body is going to replace that glycogen. It's an imperative to it. Has to happen. The way it does that is with carbohydrates.

So lets say the next day you eat 175 grams of carbohydrates. That's 700 calories.
On workout day one, 489 of those calories will be converted into fat, because your glycogen stores are full.
On workout day two, only 81 calories will be converted into fat, because it takes a LOT more glycogen to replenish your stores.

So, over time, you will end up losing more fat with the higher energy workouts because you aren't gaining as much back. Make sense?

Wow, this makes so much sense. Thank you! I mean I knew I wasn't getting lean walking the dog, but this is a great explanation why

Azdak

Bottom line up front: don't sweat it. Burning more is almost always better.

Now for the explanation:
When doing exercise like this, your body has two energy sources. One is to mix fat with oxygen (aerobic exercise). The other is to use the glycogen stored in your muscles (anaerobic exercise).

The fat burning process is relatively slow, and can't keep up when energy demands are high, so it turns to glycogen use.

When you're doing high intensity aerobics, some of the energy comes from the fat, some from the glycogen, right? The exact amount varies on the person. So lets look at your two workouts.

On day one you burned 430 calories, right? Lets say it's accurate and that 219 fat cals and 211 glycogen cals.
On day two you burned 711 calories. Again, assuming accuracy at 92 fat cals and 619 glycogen cals.

Now, your body is going to replace that glycogen. It's an imperative to it. Has to happen. The way it does that is with carbohydrates.

So lets say the next day you eat 175 grams of carbohydrates. That's 700 calories.
On workout day one, 489 of those calories will be converted into fat, because your glycogen stores are full.
On workout day two, only 81 calories will be converted into fat, because it takes a LOT more glycogen to replenish your stores.

So, over time, you will end up losing more fat with the higher energy workouts because you aren't gaining as much back. Make sense?

Wow, this makes so much sense. Thank you! I mean I knew I wasn't getting lean walking the dog, but this is a great explanation why

Unfortunately not that simple.

No common energy currency: de novo lipogenesis as the road less traveled (Hellerstein).
Am J Clin Nutr 2001;74:707–8.

In the hierarchy of fuels, dietary carbo- hydrate appears to have a higher priority for oxidation than does dietary fat; when both are present, carbohydrate is chosen. The 2 major macronutrient energy sources (carbohydrates and fats) are not, however, interconvertible energy currencies. Fat cannot be converted to carbohydrate in animals because animals lack the enzymes of the glyoxylate pathway, and carbohydrate is not converted to fat because of a functional block of uncertain cause.