Calories burned

njee20

My Garmin reckons 736 this morning, 34 minute/10 mile road ride in, 155 bpm/195 watt average, and 1845 calories for 1hr 40 road ride home yesterday, 29 miles, 154 bpm/198 watts.

There's no real consistency either - my last race at Margam was 188bpm for 2hrs 3, and yet it only reckons 1411 calories - so it thinks my easy spin into work with about 500ft climbing is burning more calories than a 2 hour MTB race with over 3000ft of climbing!

Counterproductive as training data I reckon!

evo3ben

is that an average of 188bpm over a 2h race!! :shock: or a max hr?

njee20

Average :-)

Actually ends up as 189 average, 200bpm max when i upload it. Clicky. Horrible race - boiling hot, lots of climbing, and really muddy! Still, only 1400 calories, compared to my steady ride home tonight here, which was 1500 :roll:

evo3ben

Damn thats some going over 2 hrs! with all the factors in play i suppose everyones hr would be over there normal race average.
I only got a heart rate monitor two weeks ago and now started interval training etc but the other day i thought i would go all out and do a 25k route best i could and only averaged 165bpm, thought i was doing well lol was a bit up and down though and dry.

Back onto the Calorie count though, i have seen some differences as said above. Same route, conditions etc and a very noticable difference in Cal burned. dont pay much attention to them now.

njee20

Different people have different HRs, mine's always been high, that's not a particularly high average, used to get 195, with a max of 210. You certainly shouldn't take a lower HR as an indicator of performance.

I have to wonder how the Garmin does actually calculate it - it's like it uses HR, but when power's available it uses that, and estimates far higher.

Tank-slapper

Here you go:

http://www.dcrainmaker.com/2010/11/how- ... armin.html

njee20

So my 705 obviously uses power data when it's available, and is stupidly inaccurate, then HR data when it's not, and is more accurate.

Tank-slapper

No, read the article.

Your 705 uses speed-distance-weight primarily and uses the power meter as the fallback. It doesn't use HR at all for the calorie calculation. The power meter is the least accurate method because it measures power (joules) and not energy (calories).

njee20

Fair enough, must admit I skim read it - thought it was saying HR, then power if available, or speed/distance if neither was available.

So... despite having useful data on hand (in HR) it makes it up even more than it needs to. Very odd. I'm sure it doesn't give a calorie consumption if I don't have my HR strap though :?

weeksy59

Without reading... how does it do it when i train in gym ?

Tank-slapper

njee20 wrote:

So... despite having useful data on hand (in HR) it makes it up even more than it needs to. Very odd. I'm sure it doesn't give a calorie consumption if I don't have my HR strap though :?

Yes, unfortunately. I read in another forum that it is something to do with the royalties on the HR/calories algorithm. If Garmin were to make it available as a firmware upgrade, they would have to pay each and every time someone uses it. Or, have the users pay. The speed/distance calculation is probably accurate enough for most peoples needs anyway. If not, you will have to upgrade to a 500 or 800.

Try without your HR strap and report back. It would be interesting to see what happens.

weeksy59 wrote:

Without reading... how does it do it when i train in gym ?

I have tried my 500 while riding a static bike in the gym and it did produce a figure for calories burned. The figure was quite a bit higher than the figure produced by the bike, which doesn't use HR in its calculation.

njee20

Yes, it does still give a reading, and it seems reasonably consistent with the data with HR. Strikes me as a totally pointless feature when it's clearly so inaccurate - anyone who is daft enough to think it's accurate will end up doubling in size!

MattJWL

andyrm wrote:

Around 800ish per hour for a fast XC ride, around 1000 per hour when racing flat out. They are pretty tried and tested figures from several training coaches and racers I know and are what I work to.

Funny enough, that's not far off the results I get from my Polar. I'm not fit or talented, but I try VERY hard on my rides, and there's no way I could burn 4800kcal on a 3 hours ride. More like 3000 on a 4 hour ride.

Tank-slapper

njee20 wrote:

Yes, it does still give a reading, and it seems reasonably consistent with the data with HR. Strikes me as a totally pointless feature when it's clearly so inaccurate - anyone who is daft enough to think it's accurate will end up doubling in size!

It seems quite accurate to me.

The 2 rides you mentioned earlier as examples - the race and the gentle ride home - are very different. Although you may have worked harder during the race, it was only 24km. The ride home was nearly double that at 47km.

In terms of calories burnt, the much greater distance of the easy ride is enough for the total calories to be higher than that for the race. But, in terms of calories per kilometre, which reflects the amount of effort put in, you burned far more during the race at 58 per km than the ride home at 32 per km.

Anonymous

Tank-slapper wrote:

It seems quite accurate to me.

Define accurate.

njee20

The 2 rides you mentioned earlier as examples - the race and the gentle ride home - are very different. Although you may have worked harder during the race, it was only 24km. The ride home was nearly double that at 47km.

In terms of calories burnt, the much greater distance of the easy ride is enough for the total calories to be higher than that for the race. But, in terms of calories per kilometre, which reflects the amount of effort put in, you burned far more during the race at 58 per km than the ride home at 32 per km.

The distance is totally irrelevant (as is the speed) - the race was longer and more intense, your body doesn't care how far it travels - just how hard it's working and how long for. HR (and power) are measures of intensity within a finite scale, so they're far more appropriate metrics to determine energy consumption.

If I coasted down a hill with a following wind and sat at 50mph and 90bpm the Garmin would show I used more calories than when I turned around at the bottom and rode back up - which is just wrong!

Tank-slapper

njee20 wrote:

The distance is totally irrelevant (as is the speed) - the race was longer and more intense, your body doesn't care how far it travels - just how hard it's working and how long for. HR (and power) are measures of intensity within a finite scale, so they're far more appropriate metrics to determine energy consumption.

If I coasted down a hill with a following wind and sat at 50mph and 90bpm the Garmin would show I used more calories than when I turned around at the bottom and rode back up - which is just wrong!

The 705 uses distance and time to calculate the calories burnt, so they are hardly irrelevant.

Riding down a hill and then riding back up it would result in exactly the same number of calories burned (on a 705). This is because all the factors used in the basic distance/time calculation are equal - same distance, same speed/time ratio (e.g. 10kmh for 1 hour is the same as 1kmh for 10 hours).

Yes, yes, I know it doesn't feel the same and that is why calculations using VO2 and HR are more accurate.

However, if you ride mainly circuits starting and finishing at the same point, the 705 should be reasonably accurate. The differences between climbing and descending and the wind direction would tend to cancel out, especially over long rides.

yeehaamcgee wrote:

Define accurate.

In the case of distance/time calculation 65-80% accuracy
HR calculation 90-93%
VO2 c.95%

njee20

The 705 uses distance and time to calculate the calories burnt, so they are hardly irrelevant.

You misunderstand. I'm saying that the calorie consumption thing is meaningless, and that is because the data is meaningless in the context it is used!

Tank-slapper

You are right, I don't understand what you are trying to say. Please explain.

njee20

That the calorie consumption function on a Garmin 705 is essentially meaningless as it uses data which bares no relationship to calorie consumption, despite having such data available.

Yes there will be times when it'll be 'about right', but there are more times when it will be really really wrong!

Not that difficult is it!?

Tank-slapper

Obviously you don't really know how calorie consumption calculations work or even have a grasp of basic physics and maths. Have a read here:

http://www.cptips.com/energy.htm

njee20

Right... That shows that calorie consumption is linked to work. Speed is not inextricably linked. You do not consume more calories the faster you ride - agreed? That suggests that as you coast down a hill getting faster you progressively consume more calories (on an instantaneous basis obviously) ad infinitum, which is stupid.

Your body does not know how far or fast it is going. It knows how hard it is working and for how long. If you ride at a higher intensity you consume more energy. In lab conditions you can link that to speed, but not in the real world. My road/MTB comparison proves that. It is biologically impossible for the body to consume more energy whilst working 30% less for half the time. Again, the distance is totally irrelevant. Your body doesn't have inbuilt GPS!

Obviously you don't understand how the body works or even have a basic grasp of biology. Using speed as an expression of work is inaccurate. Less of the condasention please!

Anonymous

Scientifically, it should take the same energy to move, say, a 100 kilo load 100km, whether that's done instantaneously, as in an explosive release of power, or done over a whole day.
I don't know, but I suspect, that the human body works in the same way.

njee20

Nah, not that simple! Does a marathon runner use the same amount of energy as someone who cycles alongside, on a TT bike, at exactly the same pace, freewheeling most of it? They cover the same time and distance, but have very different energy requirements.

Edit: although I agree with you in lab conditions, as I said above, there are too many variables in the real world for that to stand up.

Tank-slapper

Yeehaamcgee is right. The energy will be the same. There will be a huge difference in the amount of power used though!

Of course it takes more energy to ride faster, as it does to ride further and if you weigh more, etc, etc and your two rides demonstrate this very nicely. If your Garmin 705 was only using speed/distance data in it's calculations, the calories for the road ride would be about double that of the MTB ride. But, because your 705 is also using the power meter data in it's calculations, it gave closer readings of 1800 for the road ride and 1400 for the MTB ride. You obviously expended more power during the MTB ride, but not so much more that you burned more calories in total.

You mention real world examples, but then back up your argument with freewheeling downhill which is basically hypothetical. No ride I have ever done has been 100% freewheeling and the vast majority are circuits with equal ascent and descent. Over the course of a ride, freewheeling time and other errors tend to cancel out and the accuracy of the calorie data improves. Taken over several rides, it will become even better still.

Out of interest, do you have the power meter readings for those two rides?

njee20

Nope, only got a PowerTap on the road.

Do you actually reckon you burn twice as many calories/hour riding easily on the road vs a seriously hilly, muddy MTB race?

Anonymous

njee20 wrote:

Nah, not that simple! Does a marathon runner use the same amount of energy as someone who cycles alongside, on a TT bike, at exactly the same pace,

Nope, because one is running, one is cycling. Running is harder work than cycling, since it less efficient

njee20

Nope, because one is running, one is cycling. Running is harder work than cycling, since it less efficient

That's my exact point, the Garmin doesn't know that - riding an MTB uses more energy than the road, but that's not reflected either!

Tank-slapper

njee20 wrote:

Nope, only got a PowerTap on the road.

Do you actually reckon you burn twice as many calories/hour riding easily on the road vs a seriously hilly, muddy MTB race?

That isn't what I said, in fact I don't think anyone has said that. How do you figure 1800 to be twice as many as 1400?

njee20 wrote:

That's my exact point, the Garmin doesn't know that - riding an MTB uses more energy than the road, but that's not reflected either!

No-one has said that it doesn't. Your contention was that the figures given by computers for calories burnt are useless. I say they are not.

njee20

From my post on page 2:

My Garmin reckons 736 this morning, 34 minute/10 mile road ride in, 155 bpm/195 watt average, and 1845 calories for 1hr 40 road ride home yesterday, 29 miles, 154 bpm/198 watts.

There's no real consistency either - my last race at Margam was 188bpm for 2hrs 3, and yet it only reckons 1411 calories -

34 minute road ride - 736 Calories = c1400/hour
123 minute MTB race (20% higher intensity) - 1411 calories = 700/hour

1400 = 2 x 700, ergo, it's suggesting that my easy road ride used double the Calories as my MTB race (assuming same length).