5K effort won't burn any fat? O_o

jmoneygrip

Agreed, at that heart rate that was a sugar burn. Slow it down to burn fat.

tfanlegacy

@herlas My suggestion is to adjust the zone setting, it appears your zone setting is too low, been able to work out at zone 5 for nearly 14 minutes indicates your maximum HR maybe set too low(now at 200 perhaps?).

There are a lot of articles about how to get your max HR with a field test, or laboratory test if you want (get your Vo2Max as well), once this is dialed in, you should get a correct reading from your watch I believe.

herlas

This was a 5K race all out type effort my max HR is indeed 191 bpm, was surprised that 0 g of fat got burned, my zones are okay

jim russell

@herlas

I used to read up a lot on this kind of thing but my memory is a bit hazy…from what I remember this is probably correct . As far as it looks, you were running for 20 minutes “as fast as you can”…in evolutionary terms you were frantically running away from a lion! As other commenters said, I think the body will definitely not use fat for that, it’s much less efficient for making the muscles contract at high speed - I think the body would only use glycogen stored in the muscles and liver for an all-out effort like this (there is plenty enough glycogen stored for a very hard 20 minute effort).

Also I think I remember that the fat burning mechanism takes a little while to “switch on” so might not happen so much in shorter exercise sessions anyway.

As I said though, it’s a long time since I read all this stuff, so my memory might not be quite right!

margusl

@herlas , it’s just a model (all models are wrong, some are useful) , doesn’t mean that you didn’t burn a single gram of fat during those 21 minutes.

But generally all-out efforts are like that, ~ 95% or so of energy comes from burning carbs.

Just a (semi)random image, but the right edge (i.e. % of metabolic substrate usage vs max effort) of most of those graphs looks pretty much the same:

https://www.researchgate.net/figure/Relative-use-of-fat-and-carbohydrate-as-metabolic-fuels-depends-on-exercise_fig5_47545323

ChrisA

@herlas I think zero gramms is actually not true, but like already said, your body uses stored energy depending on how fast the energy is needed by the muscles. Metabolism of fat to a Form of energy is a slow process while metabolism of carbohydrates goes much faster. You spend most of your time in high HR zones where the energy demand of your muscles is high and getting it by using the stored energy of your body’s fat wouldn’t just go fast enough. I am pretty sure to remember that the fat metabolism also starts when your activity goes longer than a few minutes to deliver energy from fat too, so I would have assumed that there would be at least 1g or so… Polar has a lot of blog articles about this, since training with HR Zones is their big theme

https://www.polar.com/blog/heart-rate-goes-scale-goes-right/

Dimitrios Kanellopoulos

I don’t eat carbs and I do best efforts. So where does my energy come from ?

The perhaps answer to this comes to studying blood glucose and how your body metabolizes fat but also when and how it’s stored.

ChrisA

@dimitrios-kanellopoulos if you don’t eat any carbs your body generates „ketonebodies“ after a few days, which are generated from fatty acids from the fat you eat and which then are used for fast energy use and also for your brain (which normally runs on carbohydrates alone). Additionally your body can also transfer proteins stored in your muscles back to carbs, so when eating no carb/low carb in a ketogen diet the right protein intake is important (too low and your body will use protein from your muscles to build other tissue where it’s needed and if you eat too much protein ketosis will not start, because your body will generate glucose out of the digested proteins through a process called „gluconeogenesis“.

I lost 10kg by not eating any carbs for some months, but I found it too hard not to have any bread, pasta or sweets and all the other tasty things

A very good (but lengthy) book in this regard is „Good calories Bad calories“ by Gary Taubes which especially tells you that eating high carb low fat diets isn’t the healthy way of loosing weight, like e.g. I was told in School

suzzlo

Agree with everyone. 0 fat (or near 0) could be ok, since you have donde very intense and “short” effort, so no time to start converting fat into energy

Anyway, as it’s being commented, I also love the “every model is wrong, but some of them are useful” sentence, because every singe body works different and a model is representing the average and could not fit 1 to 1 with our metabolism

BR

Dimitrios Kanellopoulos

@chrisa yes but on z5-z4 do you burn any fat at all ? Or do I only burn proteins (muscle based )?

Brad_Olwin

@chrisa said in 5K effort won't burn any fat? O_o:

@dimitrios-kanellopoulos if you don’t eat any carbs your body generates „ketonebodies“ after a few days, which are generated from fatty acids from the fat you eat and which then are used for fast energy use and also for your brain (which normally runs on carbohydrates alone). Additionally your body can also transfer proteins stored in your muscles back to carbs, so when eating no carb/low carb in a ketogen diet the right protein intake is important (too low and your body will use protein from your muscles to build other tissue where it’s needed and if you eat too much protein ketosis will not start, because your body will generate glucose out of the digested proteins through a process called „gluconeogenesis“.

I lost 10kg by not eating any carbs for some months, but I found it too hard not to have any bread, pasta or sweets and all the other tasty things

A very good (but lengthy) book in this regard is „Good calories Bad calories“ by Gary Taubes which especially tells you that eating high carb low fat diets isn’t the healthy way of loosing weight, like e.g. I was told in School

@Dimitrios-Kanellopoulos Burning protein from muscle is bad! It is called rhabdomyolysis and you do not convert muscle protein to carbohydrates. Your liver is capable of glucose synthesis. I would be careful of fad books stating what are “bad” and what are “good” calories. The idea of a paleo diet that our early ancestors supposedly had and we are genetically predisposed to has been largely dismissed as well. A truly low carbohydrate diet is difficult to achieve and likely not healthy. Although fatty acids provide more ATP per gram the transport and breakdown is more energy intensive than glycogen (carbohydrate) mobilization.

Training to utilize fat while running requires sustained efforts below your aerobic threshold and will maintain or replenish glycogen stores for more intense efforts that may arise during a longer run or event.

Dimitrios Kanellopoulos

@brad_olwin I have no intention to burn muscle nor stay in keto. I just don’t try. Some days (1-2weeks) I just diminish carbs from my diet, be that be that I avoid carbs mainly. It’s very difficult indeed to lower carbs to a minimum of <50g. Also I don’t do this to loose weight. From my point of view I just fast all day long (since my 24y old) pretty much and late in the evening I have 1 meal. So if it’s with minimal carbs then I do wonder how for example such “burner stats” validate. If it means I burned x-fat vs x-carbs since that might not correlate with what I ate.

ChrisA

@brad_olwin Rhabdomyolysis in my opinion is something different as it is an illness and not a normal metabolistic process unlike the conversion of protein to glucose which is completely possible and normal:

„When glycogen is used up, muscle protein is broken down into amino acids. The liver uses amino acids to create glucose through biochemical reactions called gluconeogenesis“ (University of Michigan: https://www.uofmhealth.org/health-library/uq1238abc ) and that happens as a normal means to provide the body with energy when there are not enough carbohydrates and/or fat is available.

Concerning the book by Taubes it’s title „Good calories Bad Calories“is satirical that in its conclusion he says, that the old dogma, that calories from fat are bad, while those from carbs are good is just plain wrong

ChrisA

@dimitrios-kanellopoulos as far as I understand the body burns energy from different sources depending on the duration and intensity you workout:

for fast and immediate energy, muscles use energy that’s stored in the muscle itself in form of ATP which only lasts for about 10 to 20 seconds and after that the body starts converting glucose to ATP to supply the muscles with energy (faster process) and also converts fat as a supply too (slower process). So when you workout in a high HR Zone the body supplies energy first and for the bigger part from stored glucose. As far as I understand this works for 60 to 90 minutes unless your glucose supplies are used up, why runners (not me ) who can run that long should then - or better before - resupply glucose.
The conversion of fat to muscle usable energy takes longer and therefore the constant level of energy they provide is only enough for exertions in lower HR zones but this process can then go on for hours. That’s why you can walk / hike a whole day or even longer without the need to eat something.

In the end - when talking about loosing/gaining weight - it’s not so important if the body uses fat or carbs (or proteins) as an energy source but only how many calories you burn and how many you resupply by eating food as the body can convert carbs to fat and so when using a lot of carbs as energy the body can’t turn this used up carbs into bod fat anymore.

lexterm77

Beta oxidation peaks at about 60% of vo2 max and then it goes down but never to 0 because then you are dead. Same for carbs, never goes to 0 unless not alive.

https://pubmed.ncbi.nlm.nih.gov/6571234/

There is a test on how to do a beta oxidation rate
https://www.mysportscience.com/post/2015/03/18/what-is-fatmax

Out of curiosity I will do a 12h fasting 2h depletion run one time, and then repeat same run next week with carbo loading to see if burner only relies on itensity or some other trick.

ChrisA

@lexterm77 said in 5K effort won't burn any fat? O_o:

Out of curiosity I will do a 12h fasting 2h depletion run one time, and then repeat same run next week with carbo loading to see if burner only relies on itensity or some other trick.

I am think it’s intensity based only. But would be interesting to see, if fasting and a long run afterwards would show any difference compared to one, with well supplied glucose storages.

jmoneygrip

@lexterm77 it’s intensity for sure. As suggested earlier in the discussion, as you reach a higher percentage of your VO2 max your body transitions from burning fat to burning sugar (aka glycogen). This is known sport science and a big part of heart rate zone training. The burner feature is just looking at your heart rate zone.

People are different within reason but the OP already confirmed he was at or near max heart rate, we’ll all burn sugar instead of fat in that scenario so the results are not surprising.

Dimitrios Kanellopoulos

@lexterm77 once my toe is back to business, I can share with you guys how fasted long runs or intervals look like. 24-48h fasted and blood glucose levels if you are interested.

(Might have a few data from prev days as well)

Bulkan

@dimitrios-kanellopoulos yes please share. I’m interested in.

Another topic about glucose?

MiniForklift

All of my early morning runs (unless they’re going to be longer than 30km) are fasted. Supposedly we have enough glucose available to be converted to energy for at least a couple of hours of early morning activity before we start pulling it from less desirable places