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HR vs Watts (Power) to Calculate Calories Burned
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Since I recently began training with power via my Wahoo Kickr, I'm trying to zero in on which metric would be more accurate for estimating my calories burned. The numbers are way off. If I were to go by HR for an easy ride, I'd probably be at around 350kcals burned. With power, It has me at close to 700. I'm leaning more towards HR as being more accurate, but was hoping someone better tuned into exercise physiology may be able to weigh in.

I have a basic understanding of the conversion of watts to KJs to Kcals. But what happens when you take a strong rider who can easily sustain 300 watts for a long duration and then compare myself, who at 300 watts will probably be pushing above my FTP? Over 40km my HR will be jacked and he will probably be riding comfortably, so shouldn't I be burning more calories as my lungs/heart will require more energy to keep me going?
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Re: HR vs Watts (Power) to Calculate Calories Burned [Jayy] [ In reply to ]
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Watts watts watts!

If you do a trainer ride one day at a constant 100 W for an hour, and the next day do the exact same ride but have a higher average HR (you're sick, or it's hot out, your job has you stressed, or whatever), do you think you burned significantly more calories?

If you're using watts as the primary metric for calories, the only variable or fudge factor is how efficiently your body converts caloric energy to physical work (typically around 25% efficiency). If you use HR, you're using whatever convoluted algorithm they have to get some caloric information.

Basically, if you use power, the only operation is convert watts to calories (exact calculation, no guessing!), and then divide that number by your efficiency (a best guess based on experimental data from other athletes).

If you use heart rate, the operation is take heart rate --> put into black box strava or wahoo or myfitness pal created (all of which will differ) --> get calories.

Unfortunately I couldn't find any scholarly research on how much efficiency varies throughout the population, but perhaps one of our esteemed members can enlighten us.
Last edited by: YTS: Nov 26, 14 8:19
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Re: HR vs Watts (Power) to Calculate Calories Burned [Jayy] [ In reply to ]
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Jayy wrote:
I have a basic understanding of the conversion of watts to KJs to Kcals. But what happens when you take a strong rider who can easily sustain 300 watts for a long duration and then compare myself, who at 300 watts will probably be pushing above my FTP? Over 40km my HR will be jacked and he will probably be riding comfortably, so shouldn't I be burning more calories as my lungs/heart will require more energy to keep me going?

Nope. They are simply able to burn the same amount of calories at a lower perceived effort. Think about it, they need to process a similar amount of oxygen. That oxygen requires the same ratio of fuel to burn for both of you. So they burn the same amount of fuel.

The range of effeciency of coverting a food energy to what a powermeter would measure is 20-25% for people and I do not know if evidence show that this changes with training either.
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Re: HR vs Watts (Power) to Calculate Calories Burned [chaparral] [ In reply to ]
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But wouldn't I be breathing at a much higher rate, asking my heat and lungs to work harder to perfuse all of the cells I need to keep up the effort, thus burning more energy (calories)?
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Re: HR vs Watts (Power) to Calculate Calories Burned [Jayy] [ In reply to ]
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For all practical purposes, kJ~kcal
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Re: HR vs Watts (Power) to Calculate Calories Burned [Nick B] [ In reply to ]
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Nick B wrote:
For all practical purposes, kJ~kcal

Where as a heart rate of 150bpm only means someones heart is beating 150 times per minute with no real implication as to the work being done and therefore Calories burned.

Hugh

Genetics load the gun, lifestyle pulls the trigger.
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Re: HR vs Watts (Power) to Calculate Calories Burned [Jayy] [ In reply to ]
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Jayy wrote:
But wouldn't I be breathing at a much higher rate, asking my heat and lungs to work harder to perfuse all of the cells I need to keep up the effort, thus burning more energy (calories)?

All of that "stuff" is what contributes to changes in the efficiency I was talking about. So yes, those things might account for a few percent change in your efficiency, but surely that variability is lower than what you'd get by using HR as your calorie measurement. (I say surely based on no evidence whatsoever).
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Re: HR vs Watts (Power) to Calculate Calories Burned [YTS] [ In reply to ]
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Ok I understand what you mean. All of the answers in the thread make sense. Thank you!
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Re: HR vs Watts (Power) to Calculate Calories Burned [Jayy] [ In reply to ]
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The next question you need to ask yourself regards the accuracy of the watts on the KICKR, thus the kJ, thus the cals. There have been several posts on here about people with redundant PMs who report the KICKR reads about 20 watts optimistic.
Still, even with that potential of error, you will get a better estimate on calories burned (maybe just round it down a bit).
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Re: HR vs Watts (Power) to Calculate Calories Burned [Jayy] [ In reply to ]
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What do you need it for? Is it for race day nutrition planning or just for general tracking?

As others have said when you allow for differences in efficiency, you will have a pretty good guess (or range) using wattage.

Maurice
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Re: HR vs Watts (Power) to Calculate Calories Burned [mauricemaher] [ In reply to ]
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I keep track of my daily calorie intake and expenditure
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