Garmin 500 calorie calculations are incorrect. Is there a fix?
 

Last month, I replaced my old Garmin305 with a 500. Love it except for the calorie calculation. It is very low compared to my 305 calculations, which were close to several internet references I use.
I am a 66, 5'10" and 153 lbs with a lactate threshold of 149. Yesterday, I did a 70 mi. training ride with 5850 of climbing. Avg HR was 132. The calories burned on the 500 registered 1455. My 305 registered 4510 at a 134 Avg HR on the identical ride. Internet calculations are +-3995. The error factor is consistent on all of my comparable rides. Does anyone else have the same problem? Is there a fix?

I think both are off. For an example reference, I recently did a ride of 71 miles with 5200' of climbing and my powermeter recorded 2700 Kj of work. That would be about 2700-3000 Cal. I weigh 190# currently so I would burn more Calories than you do at 153#.

Do not concern yourself with calorie calculations on your 500, or your 305 for that matter. Here's why. The calorie calculations on any computer are at best an estimate. Only with a power meter can you come close to an accurate calculation, and even then the conversion from power to calories burned is an estimate. Further, since you continue to burn calories after the ride while you recover, the number of calories burned during the ride is just an estimate of part of the total. On top of that, even if you ride 5000 - 6000 miles per year, the total calories burned as a result of riding is only about a quarter of the total burned during the year when your basal metabolism is taken into account. After spending a long time trying to make sense of bike computer-based calorie calculations, I've come to the conclusion that it's a waste of time. Some years ago the guy who developed Cyclostats software posted here that he figures most riders burn about 40 calories per mile. I figure about 35 per mile, and don't worry about it otherwise. I strongly suggest you do so as well.

Head over to forums.garmin.com and search for things like "calorie burn" and "calorie calculation". Grab a large beverage to enjoy while you read, there are many threads on this issue.

Many thanks Woodinville. Been through your home many times on my journey from Sea-Tac to Everett. Wasn't aware that there was a forum dedicated to Garmin. Old age, I guess.

Your 500 numbers are definitely way off. My 500 typically shows about 850 calories burned for a moderately paced two hour ride (about 30 miles). A ride of 70 miles should show way more than 1455 even at your light weight.

You need to update your personal information on Garmin Connect.

With your edge connected, at the top of the page select the Settings link.

Go through those and update all the personal information, weight, age. HR etc.
Then follow the instructions and let it update your Garmin 500 physical unit.

You will have to play around with the HR / Training zones as 5 zones are the least you can have. Know your resting and max and go from there.

Make these fit your known training/exercise zones and your calorie burn will be far more representative.

I stopped paying attention to the Garmin calorie data when two otherwise identical rides showed first at over 2000 calories and then about 800.

+1 If the ride duration was 4 hours, you burned ~670 calories per hour. 500 to 700 calories per hour (per my power meter) is typical for me assuming I am doing focused efforts and or climbing.

You have a power meter. I assume you are measuring Kg and converting to calories?

I actually haven't used the powermeter outside much yet. I just take the Garmin caloric estimate FWIW and don't worry about it too much. Garmin's caloric estimates seem far more realistic than what came out of a Polar HR monitor I used to use. Garmin numbers are also in the ballpark with calorie/hour estimates from Am College of Sports Medicine and other Physical Education organizations.

I'm going to take my powermeter outside a lot more this month but not so much because it gives calorie information, which I do record but actually don't care about that much. Average and normalized power... now that's another story! And average speed of course...

The belt hole method always works.

Power meters do not provide Calorie data. However, it turns out that when all the calculation are complete, that 1 Kj of energy produced correlates to 1 Calorie burned. The variable is the body energy conversion efficiency. Here is a writeup that looks correct to me. http://www.flammerouge.je/content/3_...xpenditure.htm

Unless the measurement is being done in carefully controlled and calibrated circumstances I suspect that all calorie measurements are at best estimates. Not only that but estimates of questionable value.

As the body builders say: Don't look at the scale, look in the mirror. In other words look at the results.

Not satisfactory for quantifying how much you have stimulated the local economy by extra food purchase at the supermarket... or possibly losing weight of course.

I sort of figured that from reading one of BikeWNC's posts above. I do record calorie estimates for my rides but have never really paid that much attention to it... except as indicated above in my response to Blues Dawg. The imprecise nature of these estimates has been evident to me for a long time. I'll check out the link you sent... thanks for posting.

Have used the powertap wheels outside twice and noticed that the power graphs are far choppier than when recorded on a trainer. I infer that it's harder to keep a smooth pedal stroke with varying conditions outdoors. Knowledgeable locals tell me not to change the sampling rate and to smooth, if I want, after I offload the data.

This month is going to be fun... gonna put lots of miles, outdoors, on the powertap wheelset. There will be interesting data, no doubt.

OP, I'm sorry to disappoint you but the algorithm used in the Garmin 500, while far from perfect, is much more accurate than that in the 305, which is notorious for overstating calories burned.

As far as your 70mile ride is concerned, I am a much bigger rider than you and at the level of intensity you describe I'd probably burn in the region of 2500 - 2800kcal. 4000 is absurdly high.

I'm a numbers guy and I've found (over years) the 35-40 guesstimate to be far more accurate than any other metric.

And I have both a 305 and 500. I think of their calorie calculations as comic relief.

4000 calories seems very high for a 70 mile ride. I'm a heavier rider (~240lbs) and reckon on 40 calories per mile as a baseline, maybe up to 50 if I'm pushing myself hard or going up big hills.

Based on extremely wet-finger-in-the-air reckoning I'd figure a 70 mile ride at your weight would burn somewhere around 2000 calories.

Interesting responses. Thanks all. I think I am going to take it off the screen. After having had multiple Bruce tests, I do know that I need to eat a lot of carbohydrates while riding. My system starts relying on carbs, rather than protein at 95bpm, so the caloric burn rate is something I needed to understand.

That sounds improbable, or at best an oversimplification. And typically one absorbs only around 60g of carbs per hour ( some say it is possible to raise that to a maximum of 90g) so there's no point eating more than that while riding, however many calories one is burning.

For me, at a bit over 100 pounds, I figure 20 to 25 per mile.

I reluctantly post this as I related this story the other day in another forum on this same topic and it seems most bike folks are really sensitive about accuracy in these matters.

What I related over there somewhat tongue in cheek was I did a 25 mile ride with a friend last sat from the city to the country and the destination was an old farm converted to a brewery. I set my iPhone app to record the trip plugging in some guesses at my weight and the weight of the tour bike loaded down etc and mostly wanted to record the map and distance. When we got there I stopped the app and got a report that I had burned 2025 calories. I showed it to my friend and he said “Looks like you earned 4 beers!”

I didn’t know if it was remotely close or how he computed the equivalency beer factor so fast in his head but the number seemed about right to me. I was thinking maybe a better app would display directly in beers. Maybe an empty pint when you hit start and as you ride it fills up, each successive beer could be a little mug in the top that’s a counter.

1 Watt = 1000 Joules of energy per second
1 Kjoule = 1000 Joules
1 Kcal ~= 4 Kj (4.184)
However, the average person is just under 25% efficient, so of the 1Kcal, about 25% is transferred to make the bike move. The rest is excess heat. Therefore, 1Kj measured by a Power Tap is equal to 1Kcal burned by your body. (4 x .25 = 1) It’s appx a 1:1 ratio.

Unless the Garmins actually measure power, then it's all just an estimate. Question- do the Garmins show different cal expenditures if you do 30 minutes at 20 mph on a flat into a 15 mph headwind vs with a 15 mph tailwind? Serious question; I've never used one of them (I've never even seen one...)

I agree, although it is fairly common to have carb usage exceed fat usage as soon as you get going. The switchover point is called the "metabolic equivalency point", and not having one is an indication of a lack of metabolic fitness, and a need for long base miles. And eating carb's encourages your body to burn them. If you want to improve endurance and reduce your dependency on carb's, then eat more fatty protein, and do not eat carb's on or before your rides. Eating for training, and eating for performance, can be two different things.

TMI. Ride, Grasshopper...