HR & calories
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HR & calories
Postby swaz » Sun Jun 26, 2011 11:37 am
Does this sound like a fair assessment by my 310xt??
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Re: HR & calories
Postby OutOfBreath » Sun Jun 26, 2011 1:38 pm
On a 25km ride with an average heart rate between 150 and 160 my Garmin says that I burn about 950 calories.
I don't know if that's wrong, right, or even close... I don't use the numbers as gospel, but just as a general guide as to how much effort I have put in to the ride. I don't think you could rely on these devices to be all that accurate considering how different every person's body responds differently to exercise.
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Re: HR & calories
Postby Myddraal » Sun Jun 26, 2011 2:48 pm
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Re: HR & calories
Postby swaz » Sun Jun 26, 2011 4:05 pm
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Re: HR & calories
Postby Alex Simmons/RST » Sun Jun 26, 2011 6:00 pm
No. Assuming you mean 1000kcal and not 1000cal.swaz wrote:I ride approx. 25km into work sometimes. I've put all the correct data into my Garmin and it tells me I burn about 1000cal one way. The trip takes me between 55mins to 1hr and my HR is average 145. I'm 29, unfit, 85kg.
Does this sound like a fair assessment by my 310xt??
1000kcal would require you to maintain an average of ~280 watts on your commute, not something an unfit rider would typically be expected to do.
I'd suggest it's over estimating by nearly 100%
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Re: HR & calories
Postby ValleyForge » Sun Jun 26, 2011 10:41 pm
Alex is right - 280W would be what you need to output and the garmins default to kcal. Just think of it as being generous as to how many Big Macs you can eat afterward....
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Re: HR & calories
Postby hosko » Mon Jun 27, 2011 7:40 am
I am 32, trying to get fit, 109kg.
We do 22kms in about 48 mins twice a week during our lunch breaks at work.
When I wear my HR strap, I got the other day under 500 calories listed in the computer for that time. HR was averaging 170 according to the computer.
Not sure how accurate that is but we are stuffed when we get back as it is not all flat!
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Re: HR & calories
Postby lethoso » Mon Jun 27, 2011 10:22 pm
wouldn't that be 1000kJ of work done (~250 kcal)? Or are you assuming ~25% efficiency for a cyclist?Alex Simmons/RST wrote:1000kcal would require you to maintain an average of ~280 watts on your commute, not something an unfit rider would typically be expected to do.
I'd suggest it's over estimating by nearly 100%
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Re: HR & calories
Postby open roader » Mon Jun 27, 2011 10:49 pm
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Re: HR & calories
Postby Alex Simmons/RST » Tue Jun 28, 2011 8:44 am
As a rule of thumb, 1 kJ of mechanical work done at the cranks requires us to metabolise 1 kcal of energy.lethoso wrote:wouldn't that be 1000kJ of work done (~250 kcal)? Or are you assuming ~25% efficiency for a cyclist?Alex Simmons/RST wrote:1000kcal would require you to maintain an average of ~280 watts on your commute, not something an unfit rider would typically be expected to do.
I'd suggest it's over estimating by nearly 100%
That ratio can vary depending on gross metabolic efficiency but note that:
1 kj = 0.239 kcal
GME typically ~ 19-24%
So that pretty much means a 1:1 conversion. It's really more like 1.1 : 1 give or take .1, but for a quick estimate, it's good enough.
Certainly sufficient to know that the calorie counter used by the OP is way, way off in its estimate.
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Re: HR & calories
Postby lethoso » Tue Jun 28, 2011 10:06 am
cool! interesting to know, cheersAlex Simmons/RST wrote: That ratio can vary depending on gross metabolic efficiency but note that:
1 kj = 0.239 kcal
GME typically ~ 19-24%
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Re: HR & calories
Postby BarryTas » Tue Jun 28, 2011 10:44 am
make sure the info in the hr monitor are correct ie, sex, age, weight etc
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Re: HR & calories
Postby Alex Simmons/RST » Tue Jun 28, 2011 11:30 am
OK so two riders same weight, sex, age. One has threshold power of 180W, the other 300W. Both have same HRmax & threshold HR.BarryTas wrote:swaz - borrow a polar hr monitor or anyther brand and wear that on your commute and not the garman and compare the stats
make sure the info in the hr monitor are correct ie, sex, age, weight etc
How can the HRM provide a sensible calorie estimate for both riders?
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Re: HR & calories
Postby BarryTas » Tue Jun 28, 2011 12:06 pm
Alex Simmons/RST wrote:OK so two riders same weight, sex, age. One has threshold power of 180W, the other 300W. Both have same HRmax & threshold HR.BarryTas wrote:swaz - borrow a polar hr monitor or anyther brand and wear that on your commute and not the garman and compare the stats
make sure the info in the hr monitor are correct ie, sex, age, weight etc
How can the HRM provide a sensible calorie estimate for both riders?
too much science in science
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Re: HR & calories
Postby nickobec » Tue Jun 28, 2011 12:40 pm
For example:
50 minutes at 36kmh avg HR 150 (group ride with tail wind) 1500 calories
2 hours at 20kmh avg HR 150 (return trip solo into headwind and then hills home) 1300 calories
70 minutes at 30kmh avg HR 115 (post heart attack, now with beta blockers, hence lower HR) 1600 calories
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Re: HR & calories
Postby Alex Simmons/RST » Tue Jun 28, 2011 2:10 pm
Well that just goes to show that speed is just as bad.nickobec wrote:The older Garmin (ie my 705) calories burnt algorithm is based purely on average speed, nothing to do with HR:
For example:
50 minutes at 36kmh avg HR 150 (group ride with tail wind) 1500 calories
2 hours at 20kmh avg HR 150 (return trip solo into headwind and then hills home) 1300 calories
70 minutes at 30kmh avg HR 115 (post heart attack, now with beta blockers, hence lower HR) 1600 calories
1500cal/50-min!!!
That's 500 watts at the crank.
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Re: HR & calories
Postby toolonglegs » Tue Jun 28, 2011 2:46 pm
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Re: HR & calories
Postby ValleyForge » Wed Jun 29, 2011 9:46 am
Day to day I think an HR minitor is OK, but trying to extrapolate a whole lot of extra information from just HR & speed is wildly inaccurate as we can see.toolonglegs wrote:IIRC my Polar CS200 was "quite" accurate on full out hour efforts...overestimated a bit but not too much,maybe 10%.But it hugely underestimated on recovery / endurance type rides for me...my heart rate hardly moves till I actually start working pretty hard.I won't be bothering with a heart rate monitor ever again...maybe a powermeter again one day.
And, yes, a powermeter one day..., but I'm a first-timer.
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Re: HR & calories
Postby swaz » Fri Jul 08, 2011 5:28 pm
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Re: HR & calories
Postby johnhunt » Sat Jul 09, 2011 10:20 pm
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Re: HR & calories
Postby Alex Simmons/RST » Sun Jul 10, 2011 10:15 am
The Calories you metabolise riding a bicycle can only be measured by knowing:
i. Volume of Oxygen utilisation (VO2)*, or
ii. Power output, duration and gross metabolic efficiency (GME can be determined from power output and O2 utilisation data)
* VO2 can only be measured using a metabolic cart in a lab
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Re: HR & calories
Postby leighthebee » Fri Jul 15, 2011 3:05 pm
I have dropped that by about 25% since my average H/R has dropped as it ride more comfortably.....
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Re: HR & calories
Postby Alex Simmons/RST » Fri Jul 15, 2011 7:15 pm
There in lies the problem of thinking HR has anything to do with calories metabolised.leighthebee wrote:Now I won't dispute the maths on this thread so far, as its far from my forte, but my experience has me similar to yours at burning around 1000 kCal per hour when I was unfit and working hard.
I have dropped that by about 25% since my average H/R has dropped as it ride more comfortably.....
Apart from 1000kcal/hr probably being wrong to start with, just because you are fitter and doing it more easily doesn't mean you are doing less work.
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