Ok, so I know that any kind of online calorie calculator is generally a guess when it comes to how many calories i burn on the bike. I know that a power meter and a heart rate monitor are going to be a little more accurate. I don’t have a power meter, so scratch that option. I have done vo2 testing and I’ve got that plugged inot a heart rate monitor…but I don’t always wear it on longer rides.
so, on those other days when I want to back calculate calories, I usually use the following site:
http://www.kreuzotter.de/english/espeed.htm
I’ve seen a lot of sites, and most of them are pretty much garbage. This one actually asks a lot of questions about position and equipment and seems about as good as it gets.
so my question is about accounting for wind speed. Honestly I often leave that off as most of my courses are even loops or out and back. In my mind, headwinds and tailwinds would generally cancel each other out. But i got to thinking that if its a lot of side winds that I’m fighting too, then I think I should account for something. For example, the winds were coming from the east yesterday. Let’s say they were an even 20mph out in the open-often treeless lands i rode in. Going west I have a great tailwind, going east I’m fighting the whole time, going north and south I’m fighting side winds that would like to blow me off the roads. In the site above, should I list something like a 5 or 10 mph average because I was fighting the wind in some capacity for 75% or more of the time? I’m just not sure how to go about that.
Thoughts?
…and if anyone has a better online calculator they use, please let me know.
You’re right that these calculators are very much a guess at the calories - the easiest way is to use a power meter and estimate your efficiency (power meter measures how much actual work is done, not how much fuel is used up by your body - usually around 4-5x more IIRC). As far as the wind is concerned, the winds don’t really cancel out since you will expend more energy with a head/tail wind combo than windless conditions. You lose more speed with the head wind than you gain with the same tailwind due to the theoretical square law for aero drag. Then there’s the cross wind issue and all of the other details of the course that the calculator can’t see. In general, I don’t think you’ll get a terribly accurate guess either way with this, you could just make an assumption about the wind and it would likely not contribute hugely to the (already large) error.
Example - I plugged in the stats from my ride today (15mph wind, rolling hills, looped course - but used no wind and flat as inputs) and it predicted 2508 kcal, whereas the value I got from integration of the power file was around 1900kcal - probably due to the value for predicted CdA being too low (edit: too high). The wind and hills assumption would tend to decrease the total calorie estimate, which is obviously too high. This tells me that the estimate of wind is probably the least of your worries.
Yeah, estimating Calories burned during exercise without a power meter is tough and most of the on line tools are little more than swags at the problem. The calculator you linked is pretty good for estimating power and power is very good for estimating caloric burn. But if your rides are pretty flat and you regularly fight strong winds then those estimates are going to be pretty loose.
Basically based on power it comes down to:
Energy burned per hour in kj = average watts per hour * 3.6
That part is straight physics definitions of watts joules and seconds per hour (and conversion from joules to kj)
But there’s a little over 4 kj per dietary Calorie (which equals 1000 physics or engineering SI calories just to confuse things) but that more or less washes out because human beings on the average are only about 23% (+/- maybe 4 or 5%) efficient at converting fuels to useful mechanical work. IOW people have a Gross Metabolic Efficiency of around 23% plus or minus a bit and without lab testing with a metabolic cart you can’t pin it down tighter than that.
So in the end for all practical purposes the dietary Calories required to support a power output on the bike works out to roughly the energy associated with producing that power or the 3.6APhours estimate given above.
IOW, if you sustain 200 watts per hour for an hour you’ll burn roughly 720 Calories plus or minus a bit depending on your GME which doesn’t vary much across humans in general or even that much across the athletic population.
Even if you don’t ride with a power meter that’s useful information as it allows you to do a sanity check on other caloric estimators. For instance a female riding partner of my wife was was very proud of the 3500 Calories that her heart rate monitor told her she burned in a 3 hour ride. Well that’s more than 1150 kj per hour or that means she sustained an average power of more than 320 watts for 3 hours. Seeing she weighs roughly 50 kg that’s 6.4 w/kg for 3 hours which would make her not only an off the charts world class female cyclist, but a world class pro male rider as well. The point is that power sanity checks on caloric estimates are easy to do and if you use something like kreuzotter (which is a very good power calculator) it’s helpful to see if the power estimates match any kind of reality or whether the input assumptions (including wind) might need some tweaking.
-Dave
That was a fantastic explanation 
.
I’m not sure what your impetus is for wanting this # & what the gain is from knowing whether you burned 1000 calories in an hour or 1100.
Assuming you’re trying to potentially tie this into an intake strategy, your caloric expenditure (regardless of conditions or effort) is ALWAYS going to be far greater than your intake or your maximum absorption rate. As such, whether your caloric expenditure is 700 or 1000 or 1500cal per hour, is not really relevant, so I don’t know how much time I’d spend splitting hairs on this.
You are free to use my unscientific approach:
1000 cal/hr = balls out, cant ride any harder
450 = recovery ride
.
Thanks for the great responses everyone!
So I don’t have a burning Need to know Exactly how many calories i burn, but its just something fun to think about. I’m a lightweight (think sub 140 lbs), so I’ve never had to watch calories. My wife would actually tell you that I should probably be eating more. So first of all, I like to track some of this on the big rides just for my own information. Whether I’m burning 500 or 550 doesn’t matter, but I’d like to make it as accurate as possible and then try to keep variables consistent. Wind totally throws that off of course. I know from my metabolic testing that in zone 3 heart rate, where I normally cycle, I’m burning around 500 fat calories an hour. That’s a pretty good indication to start with, but sometimes I’d like to quantify how much harder a ride is compared to another. For instance, last week I did a 62 mile ride in the morning, in the cold (37-45 degrees), with crazy wind (avg 17 gusts to 30…but more of the higher numbers as I was out in the open lands). That ride tapped me out. And I didn’t feel normal again until around 7pm that day. I only averaged around 17+ but it might as well have been 22+ as destroyed as I felt. Then, this weekend I did over a hundred: Temps 42-53, winds around 15 or so and we averaged mid 16’s. At that energy expenditure, I think I could have ridden another 30 miles or so. It just makes me wonder what the calorie toll is. At the end of the ride I was within a pound of the weight I started the day with, so I know I ate and drank well enough.
That leads to the second reason, which is trying to be better about bringing enough nutrition for the intensity of the ride. I realize I can only absorb so much an hour, but within that, I can go heavy or light. I think I figured it well on that century with 250 calories per riding hour plus some extra if something went awry and the ride went long. …which it did, so i still ended up with 250 calories per hour of total time with stops breaks, etc included. I could have used about one more little energy bar of more solid food because I got a little hungry that last 10 miles, but I was well hydrated and otherwise felt fantastic.
There you go. That’s the impetus for asking the question. Just trying to pay more attention to the details, but trying to do it consistently…while still having fun.
Thanks!