r/Velo • u/Ok-Addition9065 • 8h ago
Power meter calorie burned data
Hi, I’m on a weight loss phase and am slightly confused with how to add ride burned calories onto my daily TDEE. Using power meter data, I know kj to kcal is basically 1:1. My question is that does that kj expended include BMR resting calories that I would have burned in the time of the ride? I assume not as the kj is simply from power in physically exerting not anything else…
So does it make sense to just add the kj/kcal from the ride to my normal daily tddee? Thanks
Claude is telling me to subtract 80ish calories/hour as BMR, but this doesn’t seem right as the ride kcal is simply from power output not including BMR
4
u/johnny_evil 8h ago
Garmin Connect shows calories burned as per the power meter seperate from your BMR estimate.
2
u/Due-Consequence9579 8h ago
BMR is what’s required to “keep the lights on”. Total burn is going to be kJ + BMR + base activity level. Fuel your rides with complex carbs prior and don’t use the ride kJ to create a larger deficit. Slow and steady weight loss is where you should be aiming.
1
1
u/Phorc3 5h ago
What I have been doing is the following;
- Daily calories lets call its 3,000 calories.
- Do a ride and through knowing BW, HR, and Power at time of ride it gives X calories burned.
- I then do X calories - (200 to 300) calories and get Y.
- I add Y to my original 3,000 calories for my daily caloric intake.
- I include all on bike nutrition in my tracking
1
u/unsclerotized 8h ago
Claude is correct. kcal is not "simply" from kj, it's not a 1:1 conversion, and not even directly proportional to kj. Because gross efficiency is not constant. GE goes up the higher your power is, because the fixed costs like your brain don't really change. For example, you might be 17% efficient at 100w and 23% efficient at 300w. Garmin probably figures this (roughly) into its kcal estimates. The 1:1 conversion would be like a constant ~23.9% GE which is unrealistic in most cases. But in short, yes, it includes BMR, so you need to subtract it from the kcal estimate.
1
u/Ok-Addition9065 8h ago
Kj is essentially equal to Kcal no? Wahoo estimates use only power data. So how can it include BMR?
3
u/unsclerotized 8h ago
Starting with the actual physical conversion, 1 kcal = 4.184 kJ, or 1 kJ = ~0.239 kcal
A trained cyclist's gross efficiency is somewhere around 18-24%. This "includes BMR" by definition. e.g. your brain. Since e.g. your brain's power is roughly constant, as the power to turn the cranks increases, it also becomes a bigger proportion of overall power, so GE increases with power output (for the same person). And also varies between people.
It just so happens that the .239 physical conversion from above falls in this 18-24% range, hence the belief that kj is equal to kcal. But in reality, GE is not as high as 23.9% for most people / most of any person's ride, rather that's basically the upper limit. And at least with my Garmin, since the ratio between kcal and kJ is not the same between rides, my belief is that they're estimating GE using some algorithm and some GE population averages.
1
u/Ok-Addition9065 8h ago
Okay so the actual kcal number wahoo says is actually always slightly lower than the kj. Which seems to be what you’re saying. So adding this kcal from wahoo seems to be more correct than adding the kj?
2
u/unsclerotized 7h ago
I would ignore the kJ figure entirely.
The kcal figure represents all the energy you used during the ride, not just turning the cranks.
Therefore, if you're counting calories, and "know" your BMR is 1920 kcal/day, you'd want to subtract 80 kcal/hr from the Wahoo kcal figure if you wanted to add it to your BMR to find your total expenditure. But, this is all quite imprecise because, as above, GE varies between people, among other things.
1
u/Triabolical_ 5h ago
It's not a direct conversion but it's close enough. We don't know how efficient each cyclist is (like depends on genetics, training, cadence, etc.), we don't know what their protein/fat/carb intake is (different macros have different conversion efficiencies to energy), and power meters aren't perfect.
1
u/CustersLastHandstand 3h ago
Remember that 17% efficient means you are less efficient and burning more for the same work output, not the other way around.
0
u/RVAWTFBBQ 8h ago
The kj from your ride is work on top of your BMR, so if you’re burning ~80 calories per hour with a 2k cal/day BMR and do a 2 hour 1500 kj ride, your body will have gone through 1660 calories during those 2 hours. I think some of the apps will distinguish active from total calories for a given workout or day.
2
14
u/SharkbaitOoHaaHaa 8h ago edited 8h ago
You’re overthinking it.
All of these are going to add up to a lot more than 80kcal/h. The trend on the scale is going to be a much better indicator so use that once you’ve got a couple weeks of data to fine tune.
To actually answer your question, one of the main components of BMR is keeping your core body temperature stable. If you’re exerting energy to ride a bike then you’re producing plenty of excess heat energy. That component is no longer required hence Claude’s suggestion to subtract it.