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Comment by jeltz | Hacker News Reader

While I agree with that excerice isn't a very efficient way to lose weight I think that you understate how many calories running burns.

When I run consistently I need to eat what feels like a lot more food to maintain my weight. Running burns about 700-800 kcal per hour for me (I have a quite small build) which ends up quite a bit over a week (I run 5-8 hours per week).

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Think about it this way. The rate at which you burn calories is directly proportional to the rate at which you breathe out CO2 because that what happens with carbon you burn.

So if every day you train for an hour so that your breathing is 3 times faster, then you have additional two hours of burning in a day. 23 usual hours plus one worth 3. So you have 26 instead of 24 hours in a day.

It's way easier to put 15% less on your plate every day than to intensly train for an hour each day while keeping portions the same.

Yes but in numbers it is way more. If I bike for an hour I burn 700-1000kcal . Thats not 15 but 50% of the dayli calorie intake… i am no expert btw. My understanding is that the problem is more that after 20 minuts of sport, at a certain heart rate, is starting to burn fat…but not body fat. More free floating fat. And it takes one hour or so to start burning bodymass. So the fuel for one hour sport is what I ate before and not my bodyfat. Another example. I do mountaineering, mostly 1 week walking in the alps for 10h a day. Thats around 4000kcal more burned a day. And there I see instant results with all my friends coming with me . They get thin very fast. Around 500g of body mass a day :)

> If I bike for an hour I burn 700-1000kcal . Thats not 15 but 50% of the dayli calorie intake…

That's estimated and probably impossible.

1000 kcal is 4184000 joules, divided by 3600 it gives you around 1100W

Human at rest burns about 100W. Pro-cyclist can do additional 400W. There's no way you can burn energy at the rate of 1.1kW consistently for an hour unless you literally set yourself on fire.

EDIT:

I was wrong.

Apparently 700kcal burned per hour of cycling is a pretty realistic number. https://www.welovecycling.com/wide/2020/05/14/how-to-convert...

Also resting kcal burn might be around 1800 per day. So 40% increase in of calories burned by hour of cycling per day every day is achievable.

The question is how can you breathe out additional ~10h of CO2 within an hour?

3 times deeper breathes 3 times faster? Because that carbon has to go somewhere.

Cycling is only approximately 25% mechanically efficient, so the parent is correct. There's a lot of heat to get rid of.

Apparently 700kcal burned per hour of cycling is a pretty realistic number.

https://www.welovecycling.com/wide/2020/05/14/how-to-convert...

Also resting kcal burn might be around 1800 per day. So 40% increase in of calories burned by hour of cycling per day every day is achievable.

The question is how can you breathe out additional ~10h of CO2 within an hour?

3 times deeper breathes 3 times faster? Because that carbon has to go somewhere.

The CO2 concentration going up in the blood increases the efficiency of respiration (because it is ultimately diffusion).

You don't necessarily need to exchange 10 times the volume of air to deal with the additional CO2.

Range given for concentration of CO2 on exhaled air is 4-5%

So it looks like it could be 25% difference at most.

I doubt the 4-5% you saw is a first principle of breathing.

Why not? CO2 levels in blood must be tightly controlled. It probably can't get twice as high as usual.

If there's already 4% of CO2 in the air around you it's an immediate danger. While you can spend 10 minutes in 3%. If your body could bump up CO2 in exhaled air from 4% to 8% then you'd probably have bo problem surviving in air thay contains 4%.

Its a mix of anerobic and erobic exercis. Its hard to keep the same heart rate while biking. So sometimes the body doesnt need oxygen to burn fuel. So it doesnt exhale co2. As said I am no expert.

https://en.m.wikipedia.org/wiki/Anaerobic_exercise

That might be it. Thank you. If anyone wants to read more about it it's called Cori Cycle and it doesn't require oxygen and it doesn't produce CO2.

But you'll need to get energy eventually from normal beathing to recycle lactic acid back into glucose in the liver.

So probably after an hour of intense exercise you'll be breathing out more CO2 in the following hours as your body clears up lactic acid.

What's interesting is you get 2ATP from making lactate, but you need 6ATP to recycle lactate back into glucose.

Would that mean that for burning more calories you should have as much of anerobic excercises as possible because it's really ineficient use of glucose?

Thanks for the hint. I didnt know that one needs co2 to get rid of lactact

And to that question as said I am nonexpert. Imho sport after a certain (1h or so) time is a mix of both and should burn most calories in a healthy way. As far as I know there was a downside to having too much lactat. And burning calories aint synonym with burning body fat. Short intensity anerobic training is not atacking bodyfat in my opinion. It only uses the reserv in carbs we have anyway ( around 2000kcal) Biking is the best exercise for bodyfatburning in my opinion. If it is more than 2h.

If you are pro-athlete, I think you could, but 1kW is probably about max a human can burn for longer periods. I managed to output 500W for 5 minutes of rowing, but I'm overweight couch potato.

I think you need to account for human inefficiency. I have to burn more than 1 joule to output 1 joule on a bike. The average efficiency of a human on a bike is somewhere around 20 to 25%.

You are forgetting about the efficiency of the human body. Roughly, only 21% of your power is transferred to the bike. So a professional adding 400W to the bike is actually consuming ~1900W of power. This all matches up with their nutrition [1]. Namely

> They averaged 91 g of carbs every hour across all of the stages.

That's nearly 400 calories worth of sugar simply while riding the bike. In fact, I would say cycling is a clear counterproof of this article. Their equations are literally (calories in)*efficiency = power and they know exactly how much to feed. I don't disagree that 99% of people are better served eating less, but doing cardio for 2 hours a day + diet management will lead to very quick weight loss. "Very quick" here is 2lbs/week but people have some insane expectations.

[1] - https://www.welovecycling.com/wide/2021/07/01/how-much-do-th...

You are arguing a different point. They argued that doing exercise burns more calories than sitting idle.

@1_player said: > Your body burns incredibly more energy just "being there" than you burn moving about.

I was objecting to the word "incredibly".

You're assuming that breathing rate is proportional to CO2 breathed out, which I doubt. I barely breath any faster while running than while just sitting here, much less than 3x.

It is directly proportional because of how lungs work. The percentage of CO2 in exhaled air is roughly the same regardless of how fast you are breathing (if you don't artificially accelerate your breathing beyond what your body dictates).

Lungs can't put in more CO2 in breathed out air.

If you breath only slightly faster when you are running than when you are sitting that must mean you ran quite a lot and optimized your stride so that you don't burn much more calories running than sitting.

But more likely explanation is that you are not aware how fast exactly you are breathing when sitting and running. Try to measure it. Also take into account that you might be taking shallower breaths when you are sitting.

Just blow up a balloon when you are sitting and when you are running with your normal exhaled breath for few seconds to test it.

Also, you don’t absorb everything you eat. Actually, let me be clear: I have no evidence for this. But the fact that my weight is so consistent despite my radically inconsistent eating and exercising suggests to me that my body can regulate digestion. When I’m in a period when I’m overeating, my body just doesn’t absorb so much.

Again, more speculation, but i would imagine that metabolic disorders involve digestive regulation issues, not just lack of exercise and overeating.

TEE is what the article discusses measuring, not the energy burned during the exercises but the total in the day. The data in the referenced studies indicate the body compensates for the calories burned running by cutting back in energy use elsewhere.

I have no clue how many calories running burns, but the act of moving around leaves you less time to eat :). Getting fat in the dark winters of Sweden is more likely for me, because I'm just bored and don't want to go outside as much so I sit inside and eat chocolate.

The problem is, it isn't efficient if you are overweight :)

When I was at my heaviest weight, I could only do a normal-speed walk, which burned relatively little calories.

At my lightest, I was also having to go out of my way to eat extra calories, as I was cycling so much, and a fast 90 minute cycle would leave me light-headed if I didn't eat some extra calories.

This is primary that thing where exercising makes you more fit and in the long term more active in general. Because what was previously tiring straining activity suddenly becomes pleasurable. And if you eventually manage to stumble upon activity you actually like, it is way easier to do it then to sit at home hungry, passive and obsessed about how miserable you feel (until said person will break and eat a candy or something similar).

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