Makel

I'm waiting on the next magical watch that will answer all of our questions.... It's coming I just know it!

bbbean 

Using a power meter, I find that I typically burn 30 calories per mile at an average cruising pace. I burned around 2900 calories on a windy 5 hour century, so I'd say your ap overestimated by roughly twice.

https://connect.garmin.com/activity/530346559

Drew Eckhardt 

While I really like some marketing people, their departments are full of former English majors writing content with a deadline. Most don't have scientific training and many understandably use the internet as a source.

More cynically they can be selective about what truths they use. They can cite studies with controlled groups (for example: cyclists training 12 hours a week with body fat under 10%. My lactate threshold heart rate starting this season was the same 168 at under 180W as it is now at over 220W which is a 22% difference in energy and Calories). They can be flexible about where they look - gross efficiency is lower and therefore Calories burned relative to output at lower efforts. They can use averages - while the Withings people ethically don't advertise body fat measurement accuracy, they could use the median deviations from dcrainmaker's independent testing of 3.3% and 4.4% in athlete/normal modes although the extreme spreads are 12.8% under and 5.6% over where the later over-stated fat mass by 43% and is a big deal for an athlete targeting minimum safe weight.

That selection is biased towards what sells. In a world where people buy clothes with smaller labels and waist sizes, Esquire magazine found 36 inch pants varied from 37 to 41".

Drew Eckhardt 

Not as much as you'd expect.

Think about riders going the same speed.

Consider an extra 100 pounds which is 45 kilograms and ignore the aerodynamics.

I measured 923kj on my last fast flat 41.8 km ride (26 miles).

Multiplying 41,800 meters by 45 kg, 9.8 meters/second^2 gravity to get force normal in Newtons, and .005 for a high coefficient of rolling resistance yields 92,169 joules. That's about 92 Calories at typical cycling metabolic efficiency, or 10%.

I measured 1932kj on my 104km metric century (65 miles) with 720 meters of climbing (about 2360 feet).

Multiplying 720 meters by 45kg and 9.8 meters/second^2 gravity yields 317,520 joules which is about 318 Calories. Add 229 for rolling resistance and you're up to 547 for a 28% increase.

For a 50 pound weight difference you'd only have 5 and 14% differences.

Aerodynamics are less related to weight. Many of us are or were Clydestales due to fat which doesn't appreciably change our surface area and therefore aerodynamic drag in the same position. At my largest I was 215 pounds; in peak cycling form 138. Same height, shoulder width, and approximate drag either way.

Where they come from size there usually isn't too much variation. The average American female is about 5'5" versus 5'10" for the average man. Assuming the same proportions that's only a 16% difference in surface area and drag.

Offset that by average women having less power than average men and more larger people being in poorer shape so the speeds are lower, aerodynamic drag lower, and Calories per mile lower.

JohnJ80

I'm having a hard time with that sort of an explanation. I think that these suppliers are trying to get it right and have made good faith efforts to do so. I am using Cyclemeter by Abvio on an iPhone. When I add a HRM, the calories between that and just the straight up ride with no HRM are lower by about 10-15%. So they are taking into account the more accurate measurement using heart rate. The route I'm using is a midwestern hilly up and down loop so I start where I finish. That typically comes out at around 50-60 calories per mile in that software which corresponds relatively close to the Garmin Edge 1000.

If we were to take the 30 calories per mile, that something like a 70-100% variance between the two if we were using the 30 per mile as the basis. It can't be that wrong with a HRM where most estimates say that it's between 10-20% off of the power meter method (let's just use 15% for purposes of easy discussion). That is a massive difference in accuracy for the most studied form of exercise with respect to caloric burn there is.

So I don't disagree with the the number in the HRM or distance method being less accurate than a power meter (that's true by inspection almost) but I do think that an estimate of 30-40 is too low and equally inaccurate. If we stipulate that the argument that body weight has little impact then even more so.

J.

Drew Eckhardt 

30 may be high if you can't manage 20 MPH solo for an hour out and back on flat ground.

Tuesday May 26 short endurance ride. 17.2 MPH moving average at 142W. 26.1 miles, 801kj, 31 Calories / mile at typical metabolic efficiencies.

Monday May 25 4x10 minutes with 5 minutes rest starting at 110% of FTP. 240W, 219W due to traffic, 239W, and 215W. 17.6 MPH moving average at 155W. 33.7 miles, 1101 kj, 33 Calories / mile.

Week of 5/18 through 5/24. 13:50 riding, 210 miles, 5849kj, 28 Calories / mile.

Not including ~30 easy commuting miles that breaks down to

Saturday May 23 endurance ride with 1400 feet of climbing. 15.4 mph moving average. 47.3 miles, 1395 KJ, 30 Calories / mile.

Friday May 22 rest day. 13.9 MPH moving average. 26.6 miles, 595kj, 22 Calories / mile. Every hard day must be balanced by an easy one to restore freshness for what follows, or time off the bike which would not be much fun.

Thursday May 21 threshold ride. Had a nice uninterrupted hour in the middle covering 20.4 miles using 207W (.94 intensity factor). 20 MPH moving average at 197 Watts. 26.2 miles, 948 kj, 36 Calories / mile.

Wednesday May 20 rest day. 14.2 MPH moving average, 26.2 miles, 594 kj, 23 Calories / mile.

Tuesday May 19 short endurance day. 14.9 MPH moving average, 26.1 miles, 643kj, 25 Calories / mile. I'm often spent after my hard day.

Monday. May 18. FTP test with a maximum 20 minute effort (230W); then 10 minutes rest and another 20 minutes in which my tired legs didn't break 100% at 213W. 18.3 MPH moving average at 175W, 26.2 miles, 919kj, 26.1 miles, 35 Calories / mile.

I don't ride Sundays.

Week of 5/11 through 5/17. 13:39 riding, 207 miles, 5693 kj, 27 Calories per mile. Almost the same as last week although I kick off each mesocycle with 3x10 starting with a maximal effort.

Week of 5/04 through 5/10. Rest week ending my mesocycle. 14:01 riding, 205 miles, 5015 kj, 25 Calories / mile. You need recovery time for your body to adapt; which in my case was a 10W FTP increase.

4/11 metric century, typical endurance ride when not fatigued from hard efforts. Skipping the time meandering between parking, cue sheet pickup then back to the ride 2360 feet climbing, 16.3 MPH moving average. 63.2 miles, 1897 kj, 30 Calories / mile.

etc.

RR3

Drew's numbers match mine.

Secondarily, most cyclists eat and drink too much on rides.

JohnJ80

That still doesn't square against the published research which was the basis for the numbers in most of the computers and what nutritionists and others are using. There is a discrepancy that needs to be explained and your data based on your instruments and performance is supposed to invalidate all the other research? While that may be possible, it does seem to stretch credibility considerably.

I'm not arguing that you are right or wrong, what I am arguing is that there needs to be something that squares this up with what you are doing compared to the rest of the research. The discrepancy is significant (i.e. gross) and something is way off. I don't think that it's as simple as saying what you have is right and everything else is wrong.

J.

Willbird

I think I need to develop an ap that credits the user 250,000 calories per hour, let people get addicted, then revise it back to a number approaching sanity :-).

JohnJ80

The problem is we have conflicting and unresolved versions of "sanity." So, you basically have the thing backwards.

J.

Willbird

Anything under 250,000 calories would be "more sane" :-).

JohnJ80

I took that for sarcasm and discounted accordingly.

j.

gregf83 

No it's not the most studied parameter. Research is seldom governed by how easy it is to do in a lab. I didn't read the whole thread but which peer-reviewed data does Garmin use? I thought they licensed their Caloric estimation algorithms from Firstbeat technologies for at least some of their devices.

gregf83 

Depends how fast you ride. The faster your ride the higher calories per mile. My rides are in the 40-48/mile range (assume 1.1 x kJ)