Calorie Burn question

mr_eddy

I was just wondering if you burn the same number of calories doing the same bike ride as your fitness increases. For example my ride home from work seems a lot easier now than 6 months ago. All the variables are basically the same, I weight the same as 6 months ago, I am on the same bike and travel the same speed and get home at the same time (give or take 5 mins) its just that now I get home and feel fine yet 6 months ago when I first started the new route I was bathed in sweat when I got home.

According to some fairly generic calorie calculators my 1 hour ride home @ 15 mph average burns around 600-900 calories however 6 months ago it felt as though I had burnt about 10'000 and now it feels like I barely managed to shift the Twix bar I have after lunch.

Maybe someone with heart rate monitor / health monitor etc can shed some light ?

So the question really is assuming all variables are equal (weight, time, weather, bike etc) do you burn more calories as the ride becomes easier ?

Cheers

mrdsgs

surely less, because your body is not working as hard! "speed" is irrelevant to calories burnt, looking at average heart rate would give you a simplistic way of comparing two rides in terms of actual effort but there is so much more involved. Using my Garmin calorie estimate, which I am sure is wildly inaccurate, 60 mile ride yesterday in 3 hours including 10 hard miles close to my limit, through and off , calorie consumption 1600. 70 steady miles today in 4 hours but 3600 feet of climbing, calorie consumption 1600.

charlie_potatoes

.....but your metabolism should be faster now?

phreak

I think this is a decent way of working out your calories burnt

To work out energy expenditure in joules, you multiply average power (/1000) by time in seconds. Thus, the work done in 1-hr at 190 W avg is 684 kj (0.19 x 3600). To convert this to kcal you divide by 4.18, i.e., 164 kcal.

However, the human body when cycling is only around 25% efficient (normal range ~ 20 - 26%), thus, this needs to be calculated, to work out the human energy consumption, i.e., 164 / 0.25 = 656 kcal.

ric/rstsport

if conditions (i.e., passing cars, air temperature, wind speed, position on bike, bike equipment, etc, etc) are *exactly* the same (which of course they couldn't be ) and you rode at the same speed then your power output would be the same. If your power output was the same, then you can calculate your mechanical work done (power * time as explained above). Mechanical work done (which is energy in Kj) would be the same. You then just need to know your efficiency which would be similar but possibly not the same (or possibly it would, efficiency can change over long periods of time). So, it's likely that if all conditions are the same then you've expended the same (or very similar) amount of energy.

heart rate monitors have nothing to do with this whatsoever, as heart rate monitors only tell you how fast your heart is beating (which is only a vague proxy for how much work you're doing). you need a power meter to show you how much energy you're expending (mechanical work done). We tend to presume that efficiency stays static (as you need to measure expired respiratory gases to work out efficiency) and swap the amount of work done in Kj as the amount of energy expended in Kcal. For e.g., i expended about 2000 Kj on my ride today (as measured by my power meter), i just say that's 2000 Kcal i burnt (although it'd be slightly different in reality depending how efficient i am).

phreak

And for clarity Ric, efficiency is bodily efficiency rather than cycling/pedaling efficiency?

Herbsman

If your power output and the time taken was the same, let's say 230 watts for an hour, then the only thing that would change the number of calories expended would be metabolic efficiency.

However, the fitter you are, the more power you will be capable of producing for a certain time, so you could potentially end up burning more calories on the same ride. It just depends how much less time the ride took as a result of the increased power output, versus how much the power output increased.

Alex_Simmons/RST

phreak wrote:

And for clarity Ric, efficiency is bodily efficiency rather than cycling/pedaling efficiency?

Efficiency is always a measure of the energy output of a system as a proportion of the energy input.

In this case it's mechanical work done at the cranks as a ratio of the total energy metabolised. Typically for cyclists it's ~22% give or take a few %.

phreak

Thanks Alex. Does that efficiency change the better you become at cycling?

Alex_Simmons/RST

phreak wrote:

Thanks Alex. Does that efficiency change the better you become at cycling?

Yes, although longitudinal studies are a bit thin. Bear in mind that on average, efficiency of pro cyclists is not that much different to well trained club racers.

Generally an increase in efficiency is associated with a lot of training over many years but it's reasonable to expect some efficiency gains in the early years of consistent quality training.

Also of course acute variations in efficiency do occur due to a wide variety of things (e.g. environmental conditions, diet, fatigue, state of glycogen stores, hydration etc), as well as the nature of the ride itself (e.g. lots of repeated anaerobic work reduces overall efficiency).

phreak

Presumably though the extra calories you'd burn by having higher power output would still be much higher than any potential 'loss' through being more efficient?

In other words, the better you get, you're very likely to burn more calories, even if you do get more efficient.

buckles

Yes... if from untrained to trained your efficiency went from 22% to 23% that's only a 4.5% increase... however I'd expect my FTP to increase much more than that...

mclarent

Just to add to Ric's example, if you're fitter in reality you've probably lost weight, which means that in Ric's example with identical conditions / speed you would require less power to push yourself along (and burn less kj) to achieve the same output, i.e. you'd burn less calories.

ric/rstsport

mclarent wrote:

Just to add to Ric's example, if you're fitter in reality you've probably lost weight, which means that in Ric's example with identical conditions / speed you would require less power to push yourself along (and burn less kj) to achieve the same output, i.e. you'd burn less calories.

potentially, or possibly, if you've lost fat mass (and i don't mean something like 20 kg, but say a couple as most people lose moving from winter to summer) and the ride is flat, it might not make any difference whatsoever to your power (that is, on flat roads mass has little effect on power when small amounts are being altered such as in weight loss). furthermore, losing fat mass *could* have a negative effect on CdA (i.e., CdA increases in some people who lose weight).

However, when i said identical conditions, i meant everything being identical except a change in fitness (power output).

mclarent

Yeah, didn't misunderstand your example, I mention that as the OP sounds like someone who's just started riding "seriously", so "quick wins" means he's prob lost a reasonable amount of weight. CDA is another thing, I was thinking more power to weight, obviously ignoring body composition questions. I also missed the bit where he says he weighs the same!

mr_eddy

So basically as a very general summary it could be set that if all variables are equal (I know that is technically impossible) then despite the same ride seeming 'easier' the mechnical work required and therefore the energy expended to handle that work load would not be vastly different from the same rider who found the ride 'hard'

Thanks for all the imput its fascinating reading.

drlodge

phreak wrote:

I think this is a decent way of working out your calories burnt

To work out energy expenditure in joules, you multiply average power (/1000) by time in seconds. Thus, the work done in 1-hr at 190 W avg is 684 kj (0.19 x 3600). To convert this to kcal you divide by 4.18, i.e., 164 kcal.

However, the human body when cycling is only around 25% efficient (normal range ~ 20 - 26%), thus, this needs to be calculated, to work out the human energy consumption, i.e., 164 / 0.25 = 656 kcal.

So quick "rule of thumb", its about 10 kcal per minute burnt, or 600kcal per hour for Mr Sporty Average.

Looking at my ride last night, which was pretty tough over quite a few hills averaged 17mph:
2h 17m duration, 1,700 kcal (according to Strava, with HRM) which is 12kcal / minute. Looks reasonable.

bigmonka

When you're driving a car you have the option of driving in an economic way or an unecomonical way (e.g. accelerating quickly away from traffic lights only to then slam the brakes on quickly after). I would guess that this is the same with cycling - being in a granny gear and unnecessarily pumping your legs away has got to be less efficient than being in the 'correct' gear. This will make the ride feel quite different for the rider, I'd assume.
But I guess that what has been said above is that a rider's efficiency is only ever in quite a narrow range (20-26% quoted above) and therefore wouldn't make much of a difference. Does that sound right?

buckles

BigMonka wrote:

When you're driving a car you have the option of driving in an economic way or an unecomonical way (e.g. accelerating quickly away from traffic lights only to then slam the brakes on quickly after). I would guess that this is the same with cycling - being in a granny gear and unnecessarily pumping your legs away has got to be less efficient than being in the 'correct' gear. This will make the ride feel quite different for the rider, I'd assume.
But I guess that what has been said above is that a rider's efficiency is only ever in quite a narrow range (20-26% quoted above) and therefore wouldn't make much of a difference. Does that sound right?

The 20-26% figure is for METABOLIC efficiency. Not mechanical efficiency.

Even so, the difference between 20 and 26 is 30%, almost a third. That would be a considerable difference.