[Closed] How low can you go?

Your calorific output is based on a HRM or similar and therefore not accurate (and usually overstated IIRC?)...his may be more accurate, adn he's basically a cycling machine, 25 hrs+ on the bike per week for years, his body has adapted.

Garmin estimates are massively lower than Polar for me. Polar will get me at about 800 calories an hour on the bike and 900 running, Garmin will have me at about 200 an hour for both. It's probably an accurate comparative number, nothing more.

Also you've got to bare in mind he's probably slipstreaming within the peloton a lot of the time so although its still a heck of a long way its not a direct comparison (assuming your comparing riding by yourself!)

The peleton saves a heck of a lot of work.

Garmin estimates are also complete rubbish.

My Garmin gives much higher figures than Polar, well over 1000/hour sometimes. Polar are alleged to have the most accurate calculator, not sure on what grounds though, I must admit the figures I got always seemed far more plausible than those from my Garmin.

If you look on [url= http://connect.garmin.com/activity/40046236 ]Garmin Connect[/url], his average HR was 133, so possibly not trying all that hard. It's a shame more of them don't use power, as that's more 'even' across the field. David Miller appears to have a rather low HR.

Interestingly enough the Endomondo app changes your calorie output quite significantly if you change your activity from "Mountain biking" to "Cycling - transportation"

Apparently if I mountain bike to work I burn about 650cals if I cycle to work I burn around 300!?

Now I know fat tyres add a bit of drag but c'mon!

I therefore tend to ignore this calorie information.

I guess the majority of calorie estimations are similarly crap

Polar are alleged to have the most accurate calculator, not sure on what grounds though

Polar do that 'own-index' hr test, the results of which have been found to be an indication of VO2 max according to their own research papers. Some correlation between VO2 max and HR variability in certain conditions, apparently. They then use this VO2 max estimate and your max HR figure and body weight to estimate calorie consumption. Rather than just guess an average like Garmin does.

Bear in mind, if you cycle form A-B at speed C, weigh D and have an aerodynamic drag coeficient of E then you will burn aproximately the same calories as anyone else doing the same trip, yes a TDF rider will be more efficient, but not by an order of magnitude.

So a calorie consumption based on HR and weight (what the garmin/polar computer have to work on) is innacurate as it records him cycling for 4 hours at 170bpm. If I did the same I'd burn a lot less calories and get nowhere near as far, but the computer would say we'd done exactly the same workout.

TINAS, as mentioned, Polar have an estimate of VO2 max to work with in addition.

Interesting things you can do with physics..

Remember, you are all saying calorie, but you probably mean kcal (eg: 2000kcal is daily recommended ammount for a woman)

3500m of climbing. Say the mass of him and bike are 80kg. g = 9.81

mgh = 2746800J

1kcal = 4187J

2746800/4187 = 656kcal

That only takes into account climbing, which is why its so small. I imagine that would be how some GPS devices give a rough estimate of kcals used.

If you have their power output, you can do (power x time)/4187 = kcals used.

Over the course of the Tour, Landis averaged 232 watts of power when he was on the bike. But that was just his average; in a stage like the final time trial, where Landis finished sixth, he averaged 379 watts over 75 minutes.

I found this, so take a stage of 5 hours like mentioned. And using the above formula, you get another 997kcals used. Still not close to the 2298 mentioned before. So I'm guessing his average power output was slightly higher.

Realman, you're forgetting that muscles are not 100% efficient. More like 20%.

So 656kcal * 5 = 3280

The other figure, which is directly from a power meter so probably a bit more accurate, gives you about 5000kcals.

Strong tailwind plus holding onto the team car up some of the hills while he was "having his bike looked at", or is the 2298 calories mentioned horrendously underestimated? You decide!

Hesjedal's calorie count is much lower than his team mates' for the same course, possibly because calories are being calculated from heart rate and his barely tops 100bpm when he's riding on the flat. [url= http://connect.garmin.com/explore?owner=garmin-transitions#activityType=all&eventType=all&activitySummarySumDistance-unit=kilometer&activitySummarySumDuration-unit=hour&activitySummaryGainElevation-unit=meter&owner=garmin-transitions&sortField=relevance&currentPage=1 ]Here[/url]'s the Garmin Transitions uploads for the whole team on Garmin Connect.

I know, I was trying to work it out from a GPS prospective.

Its a really hard thing to measure accurately. Maybe if you allow yourself to completely bonk, then intake a set amount of kcals and see how long you can last for, that would give a rough estimate of how many kcals you're using over time?

How do you measure kcal intake from heart rate? Do you have to calibrate it to the rider, so you can have a guess at what power their outputting at what heartrate?

you cant really corelate HR to power, att he start of a ride you could draw a kind of map/3D graph ploting power, against cadence and HR. But youd then need a 4th dimanesion soemwhow taking into account that as you get tirred you HR remains high (itss til trying to pump all that glucose/oxygen) but the blood has no more sugar in it so its not actualy having any benifit.

TINAS, as mentioned, Polar have an estimate of VO2 max to work with in addition.

I've only got the basic wrist watch version which just asks for age/weight/sex.

Polars calorie calculations are far more accurate then Garmins. Polar did studies on groups of people with different activity levels and measured the HR's against a Expired air analysis (Gold Standard for calculating calorific usage). That is why you need to put in your activity level, age, sex etc when setting your polar watch. If you put in the information correctly your polar should be damn close to the real figure. I've had the possibility to check my polar in the lab against expired air analysis a few times and it has always been within about 5% of the real figure under different test conditions.

AFAIK the Garmin calculation is based on mechanical energy rather then any physiological measures. This causes the figures to be way off. I own both devices and my Garmin never gives figures anywhere close to the Polar and I trust the Polar.

As far as energy expenditure for the tour cyclists like somebody said sitting in the peleton is quite energy saving. I've read somewhere that on a flat stage it is probably possible to hang onto the back of the peleton with a power output of 90W!!! This is achievable by pretty much any amateur cyclist so these guys are barely ticking over if they are chilling somewhere in the bunch. That obviously goes out the window on a mountain stage.

HR and power output are correlated for a given person under the same conditions. Over a period of time a phenomenon known as Cardiac Drift occurs which means that your HR will drift upwards at the same power output. This is due to dehydration and a reduction in stroke volume in the heart which means it needs to pump faster to provide the same amount of oxygen to the muscles. Its not related to glycogen levels as someone has mentioned. When glycogen levels deplete there is simply no fuel to run anaerobically so power output and HR both have to drop, but they remain correlated (with a little deviation for cardiac drift).

realman, you'll be pleased to know that your exemplary science in this thread has convinced me of the veracity of your explanations in the downhill speed thread yesterday. 🙂

Remember, you are all saying calorie, but you probably mean kcal

Those are as good as synonymous in the vast majority of circumstances, no layperson literally means calories, they're always talking kCal.

I've read somewhere that on a flat stage it is probably possible to hang onto the back of the peleton with a power output of 90W!!!

Yeah I'd go for that, although you don't want to be right at the back, better off totally surrounded by other riders.

in a stage like the final time trial, where Landis finished sixth, he averaged [b]379 watts over 75 minutes[/b].

That's mental.

Those are as good as synonymous in the vast majority of circumstances, no layperson literally means calories, they're always talking kCal.

juan - Member

It would be saying a m is equal to a Km, whereas one is thousand times bigger

in every day usage that's completely different.