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Discussion Starter · #1 ·
Givens:
If I train long and hard, I'll:

  1. Lose weight
  2. Gain pedal power, measured in watts
  3. Gain speed on the bike
  4. With or without power gains, generally, a loss of weight will make me faster

OK so here's my question: Having started in an untrained (out of shape) state, will I burn fewer calories the more trained I get?

In other words, if I'm fat and out of shape now, and I do a 1 hour ride averaging 200 watts, when I'm 9 months into training, having lost 20 pounds and gained back a personal best FTP, will I burn fewer calories in a 200 watt ride over 1 hour? Sure I'll do it faster, but will I burn the exact same number of calories?

I suspect that calories are a chemical measure of energy, and so putting out the same power over an hour equals the same amount of calories burned, regardless of my physical state, or even who I am, whether I'm a tall woman, or a short man.

I'm curious, let me know what the facts are here; thanks in advance.
 

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I think you can increase your efficiency to a degree, but I don't have any supporting data. The numbers I've read suggest an efficiency of 20-25% for the calories-in to power-out conversion.

However, if you've gained fitness and increased your FTP, you should be doing your ride at a higher power thereby burning more calories.
 
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if we're getting granular we could argue about the first three on your list but the answer is "most likely".

watts being a measure of work at a point in time and Joules/kilojoules being a measure of work over time if you have to do less work (less weight) at the same effort level (all other things being equal) you should be faster.

There's a loose correlation between work and your caloric expenditure (google says 4.2 kj per "calorie") and then you'll have to figure out your efficiency (google says somewhere between 70-80% of your calories are just converted to heat) and it looks like this can vary but.

one of the links that looked right in line with your question is from Stages and right here...they use 22% efficiency and I'd wager they've forgotten more about it than I ever knew.

You'll also get more efficient at a certain level of work. I've been doing marathons for.... (feeling really old now) a long time and I'm not trying to backdoor brag but because of that I can ride nearly all damn day in high z2 if I'm fueled and my HR might creep into the mid 130s by the end of the day (observed max 177 but there's probably a little more room there and very little growth in ftp numbers).

does that help?
 

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The answer is complex, and not my area of expertise. I will try and explain it as I understand it. If someone knows more than I please fill in the gaps.

When you are out of shape a certain wattage, let us say 200 watts, might be hard enough that you are burning primarily glycogen as a fuel source, when you are well trained at the same wattage you might be burning fat as your primary fuel source. Glycogen burning is actually more efficient than fat. So a rider burning glycogen is ultimately using less calories per hour than one burning fat. However, you only have about 1500 calories of glycogen available and 10s of thousands calories from fat available.

One the terms I starting to hear a lot is "metabolic flexibility." The idea that you want to train your body to burn fat as it primary fuel source for sub-maximal activities, but when you going flat out you want your body to switch to glycogen.

So... to answer your question, as you get fitter two cool things happen.
#1. You burn more calories per hour because you get a high percentage of your energy comes from fat.
#2. You are not as hungry after because you haven't depleted your glycogen.

Makes weight management much easier.

A couple of the elite athletes I work with can regularly do 4hr rides without needing to fuel. I on the other hand have bought a house in bonk town if I try and do 3hrs without fuel.
 

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When you are out of shape a certain wattage, let us say 200 watts, might be hard enough that you are burning primarily glycogen as a fuel source, when you are well trained at the same wattage you might be burning fat as your primary fuel source. Glycogen burning is actually more efficient than fat. So a rider burning glycogen is ultimately using less calories per hour than one burning fat. However, you only have about 1500 calories of glycogen available and 10s of thousands calories from fat available.

One the terms I starting to hear a lot is "metabolic flexibility." The idea that you want to train your body to burn fat as it primary fuel source for sub-maximal activities, but when you going flat out you want your body to switch to glycogen.
^^^This, right here. At any relative workload, trained athletes are burning a higher percentage of fats to fuel the activity than untrained athletes.

Regarding any other changes in efficiency, assuming the wattage you are monitoring is that at the cranks or wheel, then aside from any differences in efficiency related to substrate utilization, you do stand to be more efficient as you become lighter from a reduction in reciprocating weight (leg mass) and reduction in weight supported by the upper-body (so, heaving your fat torso around when pedaling out of the saddle, or even supporting your torso when seated). How much more efficient? I'm sure a cursory search on Google Scholar might reveal if anybody has measured this or not...
 

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I think too that if you're fat, you're expending calories (Watts) supporting and moving your extra weight around that you wouldn't be if you're skinny when putting out the same 200 W in both cases. It's probably not much of a factor sitting and grinding away on a stationary trainer, but riding on a trail it will be significant, IMO.
 

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Discussion Starter · #7 · (Edited)
Thanks everyone for contributing, good points all. The Stages link explains the commonly accepted formula translating from watts to Calories.

https://stagescycling.com/us/news/what-it-means-watts-to-kjs-to-kcals/

So the answer from a training perspective is that the gym and power meter industry has consented on a 22% efficiency to calibrate their exercise equipment.

As mentioned, slogging around on a bike while overweight, one would expect to expend more calories outside of the power meter during the 200w/1 hour ride-good point.

Three energy sources: food ingested on the bike, stored muscle glycogen, and fat, these three ways for the body to get energy are probably going to have different "miles per gallon," so to speak.

Not only that, but as mentioned, some people are either naturally talented or better trained at burning fat or have bigger glycogen stores-the example being some elite athletes can ride well over 3+ hours with just water. I start browning out at 2.5 hours without strictly staying in Z2.

So the simple answer is there's a commonly accepted formula for calculating calorie burn from watts, not unlike a FTP 20-minute test, but the reality is that caloric burn rate could definitely vary. As Stages mentions, is it 18-24% at the upper and lower limits? I've read that fat is almost entirely oxygen, carbon, and hydrogen atoms crammed together.

Sent from my iPhone using Tapatalk
 

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At equal workloads you burn the same calories, it doesn't matter if the fuel is glycogen or fats with a caveat mentioned by LMN (efficiency difference).

If you take into account efficiency, then the results will vary.

So in this case I believe there are 2 correct answers, the theoretical one and the practical one.

In the first it is as I first said, you will burn equal amount of calories independently of fuel source, assuming equal efficiencies.

In the second one, an untrained individual will have lower efficiencies and will use fuel sources different than the trained one. So the calories burned at a given power rate will not be the same.

Personally I think a very fit individual burns fewer calories, comparably to an untrained one, but I think its mainly because of HR difference and efficiency. On my best days when doing group rides I wouldn't even sweat in mid day and my HR was fairly low while my untrained friends were dying. Then, when I was the untrained one I as sweating and gasping while the trained ones were just okay. HR seems to play a major role on calories burned, but the efficiency gained by training in my experience is very significant as well.
 

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...but the reality is that caloric burn rate could definitely vary.
And consider individual differences in digestive efficiency...just because you ate x, y, and z grams of carbs, fats and proteins doesn't mean you actually absorbed every single one of those molecules.

Don't sweat the details. If you're counting cals in and tracking wattage/cals out, keep an eye on the trends. Don't worry if the math breaks down on paper...i.e. if you should be losing weight, but you're not, then eat less than the program would estimate; if your ride/race nutrition should cover the kJ/cals estimated, but it's not, then eat more or decrease the intensity. Acknowledge that no equation is going to account for all individual variation, and make adjustments as necessary.
 

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It's likely that you will become more efficient at using oxygen to convert food substrates to muscular work --and this is exactly what makes one person more "fit" than the other--but it's not going to really affect your daily calorie count.

It's also true that a higher volume of oxygen is needed to convert a given amount of fat to work than to do the same amount of work using carbohydrates, but that's not to say that carbohydrates are more efficient. In terms of a person exercising, we all are pretty much as efficient at using carbohydrates for fuel--they are there and we can all use them very easily. But of course this only work when and while they are available! On the other hand, the big factor separating riders of different fitness is their ability to use fat as fuel.

Someone who is more fit and more efficient will use fat at a higher rate at higher workloads than someone who is less fit and less efficient. This is great because those carbohydrates are so limited as mentioned!

This is a benefit for mountain bikers because we need those carbohydrates to go hard, but want to definitely spare them when we are recovering (like when we are coasting down a hill) or not going as hard. Sparing carbohydrates and saving them for when we really need them will allow us to go harder for longer. But if we are using those carbohydrates at too high of a rate, we will eventually run out of them...after which we will limp home with our tails between our legs...

Also, maybe a slight correction to the original question. I think training long AND hard is a tough way to get more efficient. What about long and easy? Will do wonders for being able to go hard :)
 

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OK so here's my question: Having started in an untrained (out of shape) state, will I burn fewer calories the more trained I get?

In other words, if I'm fat and out of shape now, and I do a 1 hour ride averaging 200 watts, when I'm 9 months into training, having lost 20 pounds and gained back a personal best FTP, will I burn fewer calories in a 200 watt ride over 1 hour? Sure I'll do it faster, but will I burn the exact same number of calories?
You dont have to dive too deep into the science here. Technically a calorie has a direct correlation with Watts. but in mountain biking, you are burning calories more than just the power through the pedals, which is immeasurable.

Here's something that will blow up your entire equation. If you start out at 220lbs doing 200 watts for 1 hour 5 days a week. In 9 months you may be 205 riding at 225 watts at the same perceived effort.

This equation equates to an entirely different speed on the trail where you are SIGNIFICANTLY faster.

When I first started riding, I would average 14.5 mph on the granite/bike paths on my MTB. and I was "really pushing it." Now a days with more power, less weight, better bike, Those speeds are closer to 18-20 at the same "really pushing it" effort.

Now if I went out and did a 14.5 mph ride, it would feel painfully slow and boring and I would be pushing less watts and fewer calories through the pedals. I also would probably ride 60% of the ride no handed and burning some calories through core stabilization. So executing the same ride at the same speed would be less effort and less calories and be considered a full on recovery ride. This whole scenario occurred for me over a 3-4 year period.

Remember: "It never get easier you just get faster" - Greg Lemond
 

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Discussion Starter · #12 ·
Perceived effort or speed were listed in the givens; let's focus on caloric burn this time. My idea here is just to understand that one of the benefits of any on-the-bike training on caloric burn rate, and estimate the resultant weight loss.

Calculating calories burned, in creating a workout plan, you can make sure you're able to hit weight targets for the season without crash diets, and also to know how long it's going to take to get there.

If we talk about mountain biking, yes, there will be immeasurable calories expended hucking the bike around, but will it be more or less the same if we do the same ride before/after getting in shape? Some differences due to girth, yeah sure. The real-world difference is only going to be measured on the bathroom scale, gotcha.

I think it's safe to say, after investigating, that the same workout will instill approximately the same caloric burn, and weight loss, before/after getting in shape, but it would be interesting to measure the variance.

The science I get into and find fascinating is the chemical composition of human fat--Googling it, you don't always get straight answers. From what I read it looks like that the body can grab the 3 appropriate atoms: carbon, hydrogen, and oxygen, from its fatty mishmash and turn them into the basic molecules you need to survive. This primarily comes out as expelled air (CO2) and water (H20). That's all that fat mostly is.
 

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it's simple

if you are putting out 200 watts to the crank
you will just be going faster if you weigh less

since you are carrying less weight [and
maybe a little less air resistance...]
 

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The best way to measure total calories is by putting a person in a thermal box and measuring the heat rise (or cooling input energy), while also measuring energy to the cranks.

If a person is putting 200W to the cranks, not sure what mechanisms would cause different temperature rises to the box, if a person is at different weights.

One thing for sure though, if a person is pedaling at near maximum, and has a good layer of fat on them, it is difficult to expel heat, thus making calorie output more difficult.
 
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