Correlation between HR% and Cals burnt

splattingly

[Sorry for repeat post - should have posted it in this section originally!]

Hi Guys,

I'm just looking for a bit of info about how to nutritionally replenish my workouts. Say I rode 1hr at 75% of MHR, what kind of calorie-range would I need to consume to make up for this. Would a rough amount be 1000cal per hour?

Thanks for your help,
Chris

ric_stern/RST

Chris,

Simply there is *no* correlation between energy expended and HR, other than you're likely to expend more per unit time at higher rather than lower %.

assuming you mean 1000 kcal, then you'd be riding at ~ 280 W, if you're an average sized male (~1.75 m and between say 65 and 75 kg) ride a standard road bike, and have a reasonably good position that's about 40 km/hr avg speed you'd be travelling at on flat roads.

It's only possible to calculate energy expenditure from expired respiratory gases (this is done in a lab) and for a ball-park figure outside you need a power meter (e.g., Power Tap, SRM).

As a *vague* estimate, i expend ~ 720 kcal/hr during road races, when competing in 1/2/3 or 2/3 category events. during training at zone 2 (quality endurance work) i'm expending ~ 700 kcal/hr, i'm an averaged sized male.

ric

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splattingly

Thanks for your help ric - I just thought there might have been a general rule of thumb but nothings that simple!!


Cheers

ric_stern/RST

basically, energy expended is a measure of (mechanical) work. work is equal to power output * time and is measured in kj. the amount of work you do in kj needs to be converted to kcal (divide by 4.18), but due to a bizarre quirk, cyclists are ~ 20 - 25%, and thus, you need to multiply the kcal amount of work by 4 to 5. in other words, as efficiency varies due to many factors, the original measure of work in kj can just swap it's units to kcal and that's a good ball-park figure (e.g., you cycle for an hour and expend 720 kj, just call it 720 kcal).


ric

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mattv2099

There are 'general rule's of thumb.' But they are just a ballpark. Nothing to bet the family farm on.

When fueling my body for riding and racing I've followed these ball park figures:

When I do endurance riding (17-20 mph 2-4 hours) I fuel as though I'm burning about 500 calories per hour.

If I'm racing (mountain bike, time trial) I fuel as though I'm burning 1000 calories per hour.

Works for me, although I know it's not very precise or accurate but it may be 'ballpark.'

juf2m

So in other words, my heart rate monitor, which tells me how many cals I'm burning based on my height and weight and the bpm...is WRONG???!!!!

I am a mere newbie, without experience in racing and doing heavy scientific calculations....(being a mathophobe) but I found that my heart rate monitor and my fitday bicycling calorie counter were so similar that it must be about right. For example, the other day I rode for 2 hrs and 42 minutes at an average of about 12 miles an hour and it said I burned about 1115 cals. This seemed like it would make sense, I really hope it's not drastically wrong because I'd really rather not have to do all these calculations that I will no doubt get wrong, just to figure out how many calories I am burning...

ric_stern/RST

you can't accurately calculate energy expended from a HRmonitor -- if you could you wouldn't need a power meter.

whether that estimate of expenditure is correct or not it's impossible to say. there's too many unknown vaiables to make statement on it's accuracy.

ric

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juf2m

So what is a power meter? Is it expensive? I am going bankrupt buying all these doodads for my bicycle!

ric_stern/RST

a power meter is a device which measures how much power you are producing to move yourself and your bike at a given velocity under given conditions. power is an absolute measure of the intensity of which you are riding and isn't affected by external factors (e.g., 300 W is 300 W and it doesn't matter if it's into a headwind, on the flat or up a hill!).

I recommend either the Power Tap (www.power-tap.com) which is a hub based design or the SRM (www.srm.de) which is a crank measuring design.

Prices start at ~ US$700, although at RST we can offer you a discount on these prices for the Power Tap.

ric

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juf2m

$700 US!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! *faints*

That, even at a reduced rate is a little out of my league right now. However, if I start more serious training for races etc, I will certainly consider it. I do appreciate this information, but I think more general caloric assumptions will do for me for now.

ric_stern/RST

i'm thinking that a power meter might be overkill for a "newbie", i was really just answering your query.

ric

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