A question on Calories

If I am 180cm, 70Kg with an FTP of 300W & my girlfriend is 170cm, 60Kg with an FTP of 200W & we ride for 1 hour at 100W do we burn the same amount of calories?

I think yes as we’ll both burn the same to produce the same but she thinks no given I’m working at 30% of FTP & her at 50%.

Bring on the science!

(Yes winning this debate (fight) is important enough to me to come on here and ask :slight_smile:)

You do the same work if you both ride at 100 watts, which is 360 kJ of work.

Whether you both have the same metabolic efficiency is another matter, but within +/- 5% you will probably burn the same calories.


Wasn’t this kind of discussed in the most recent Podcast?

I’d have said no. You’re both aiming for the same watts for the same time duration but, your working at a significantly lower % of your FTP.

My answer is based on this being done on a trainer where all other factors (weight, drag etc…), are equal.

Yes, @janerney 's answer is correct, including the metabolic efficiency variable

What will change, although calculating how much requires a gas exchange test, is where those calories come from. Likely yours will come more from fat than glycogen due to the % of FTP you are working at whereas hers will likely come more from glycogen than fat

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I think this is possibly one of the biggest misconceptions for beginners - because it feels hard, they think they’re burning more calories. But in fact Peter Sagan would burn exactly the same if he put out the same watts, even though he wouldn’t be sweating.

I can imagine it can lead to over-doing the recovery meals and on-bike snacks by those who are just starting out, and not actually putting out that many watts.

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Possibly counterintuitively, adding time at low intensity is way more effective at burning calories than a harder workout. Hard workouts are relatively inefficient at burning calories (unless you have limited time).

A typical tough TrainerRoad interval session might be something like an hour at 0.85 IF – so, the NP is 85% of your FTP. But the average power will run more like 70-75% of your FTP. An hour at 75% is easier but burns the same calories. 1.5 hours at 65% burns the same as a 1-hour all-out effort!

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It’s maths. Watts x No. of seconds = Joules which correlate to calories.

If you do an hour at an easy pace you will produce & use fewer calories than when riding at a harder pace. For instance i spent an easy hour today sat on the trainer watching the Tour De France and burned about 600cal. On Thursday night I raced for an hour and burned 1100 calories.

That’s an insanely easy pace on the trainer.

Imagine your racing for an hour was an all-out time trial – one hour at FTP. That’s 305 W. Now, if you were racing, it’s probably not that even a power output (VI > 1). You’ve still got to average 305 W to burn 1100 calories, so that means your NP was more than 305. A typical VI for a road race seems to be around 1.2, maybe, so that makes for an NP of 365 W, held for one hour.

Your easy hour on the trainer is 600 calories, which is 165 W. If your race was an all-out effort, that means your easy hour was at 45% of FTP. That’s really easy!

If you wanted to match the 1100 calories of racing, you could hold a constant 245 W for one hour 15 minutes. That would be less than 70% FTP. Which do you think is easier and more repeatable, racing full-bore for an hour, or 70% FTP for 1.25 hours?

To maximize calorie burn:

  • More time is more effective than harder effort. The relative difficulty of producing X watts increases quickly (faster than linear), but the actual energy consumed just increases proportionally.
  • Even effort is more effective than varied effort. Varying your work level makes the NP (the “relative difficulty”) higher than the average power (the amount of energy consumed).
  • If time is limited, use the highest effort level you can sustain and repeatably recover from.
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Here’s a really good demonstration of this from my two rides this weekend.

Ride One: a group ride lasting 2hr38mins, including 4 hard efforts that pushed my HR above 90% max for significant periods, and finishing with a little sprint up the hill to the cafe. IF was .83 and average HR 127.
Ride Two: 88 virtual kms on Zwift, 2 and a half hours, never going above 75% maxHR, staying in power zone 2. IF .65, average HR 111.

Calorie results?
Ride One: 178 TSS, 1489kj
Ride Two: 112 TSS, 1628kj

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Hello together,

I have been discussing the following question with my girlfriend for a while and we cannot agree on an answer. Possibly you can help us solve the question:

Assuming two identical riders both pushing 200 watts for an hour. This equates to approximately 720 KJ. To my knowledge the kj can be converted into kcals with the ratio of 1 to 1 (due to factors such as efficiency, etc.), hence the riders burning 720 kcal in this hour. However, how does heartrate factor in? If rider A is riding at only 70% and rider B at 90% of max heartrate, is rider B going to be burning more calories? If so, what is the reason and how can the total effect be approximated?

I look forward to an interesting discussion and insightful answers.



The heart rate is immaterial in terms of total calories burnt. There will likely be small differences in calorie burn depending on efficiency, etc, but you’d need lab testing to figure out those differences, they’re unlikely to be very large, and it could be rider A or B who is burning more.

Rider B is probably burning a lot more of those calories from glycogen stores not fat, and is also likely to have to stop a lot sooner :wink:

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Heart rate doesn’t matter

Similar discussion here: A question on Calories

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If you are both at 100w exactly and assuming you are both riding the same distance:

  • She would finish first (lower body weight)
  • You’re ride will take a bit longer, and you would burn more calories

In actuality, you are probably both riding the same distance and same speed. So your power can’t be identical. You would have to be putting out a bit more power, and correspondingly you would burn a bit more calories.

So you would burn more calories, but only because of body weight differences (not general fitness or FTP)

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This appears to link to the top of this very topic, as the question asked was exactly the same as the OP.

Maybe we can keep this going and make it a giant thread dedicated to answering the same question every 6 months…

My post is from a separate thread that the person I was replying to created. Chad merged that thread into this one because it was redundant

Ah, makes sense now! Thought I was getting deja vu…

Hello Grant,

You’re actually mistaken. When it comes to calory burning, unfortunately, we are not all created equal.

According to researches, men burn more calories than women for the same amount of effort. It’s not fair, I’ll give you that :slight_smile:

You can read more about factors that affect caloric expenditure here: https://thechamplair.com/training/how-many-calories-does-running-burn/

So your girlfriend was right. Don’t worry it won’t be the last time and she will always remind you. FTP has nothing to do with work done. It’s about joules and the efficiency of your particular body.