Diminishing returns ?

mr_eddy

Maybe someone can help with this.

Basically I have been looking at amount of calories burned for doing X number of miles etc on various websites and using apps on my phone. The general opinion is that for someone like me (29yr male, 5'10", 175lbs) cycling at an average of about 15-18mph burns around 900 calories per hour (+/- 50 cal)

However I have doubts as that number seems very high, my route home is roughly 8 miles and takes just under 30 minutes. According to the various apps etc I am burning around 450 calories each way.

I have noticed that my effort compared to when I first started some time ago has been much reduced and the speed has remained constant. Would I still be burning 450 calories each way despite being noticeably less knackered at the end of it? At the end of my commute I really am not very tired at all so I can't see how I would have burned 450 calories worth of energy

I know this seems like a daft question but I just wanted some advice. Basically I am looking for a general method of measuring calories burned each day based on my current level of fitness ( I would consider myself to be above average)

Hope this makes sense.

Thanks

sungod

calorie apps/websites/etc. are just making guesses, often extremely poor ones

i'd guess c. 300, but a strong head/tail wind would make a big difference, as would hills

the only reliable indicator of actual calories used cycling is a powermeter, even then accuracy is limited by the uncertainty between mechanical energy output and your body's actual energy use (afaik usually assumed to be c. 25% efficiency, but people vary)

amaferanga

900 calories/hour equates to around 250W average power. That's hardly mind blowing Wattage, but on rolling terrain with a bit of coasting, the odd junction, traffic lights, etc. then maintaining 250W is actually not so easy (even if you can ride at 300W or more at threshold). The difference in average power between riding at 15mph and 18mph is massive, but for me doing my 35min commute 250W would result in about 19mph average. To average 15 or 16mph would only be around 200W or ~700 calories per hour. I'm a fair bit lighter than you though.

Anyway, I'd agree with sungod - about 300 calories each way, maybe 350 would sound about right given your average speed. I'd say 450 is quite likely to be an overestimate, which is obviously not what you want to be doing.

smidsy

Interestingly the 450 cals each way you quote for your 30 min commutes is exactly the same ratio as the 900 cals per hour that you doubt so much in the first place - so forgetting the mechanics/maths of it you already knew it was wrong didn't you ;-)

amaferanga

smidsy wrote:

Interestingly the 450 cals each way you quote for your 30 min commutes is exactly the same ratio as the 900 cals per hour that you doubt so much in the first place - so forgetting the mechanics/maths of it you already knew it was wrong didn't you ;-)

I could be wrong, but I figured that the reason he asked about 450kcal each way being right was actually based on the fact that the online guesstimators had suggested 900 kcal/hour. So is your point that the OP knows how to divide 900 by 2?

smidsy

amar - No

CambsNewbie

Taking aside the exact number of calories burnt..

Say I cycle 20 miles and burn for example 1000 calories. At the end of it I'm completely knackered. I then start training hard. Six months later I then cycle the 20 miles again. Will I again burn 1000 calories because that is the energy required to travel that far on a bike, or as I become fitter does my body become more efficient and therefore may now only require 750 calories to do the same effort?

Lightning

CambsNewbie wrote:

Taking aside the exact number of calories burnt..

Say I cycle 20 miles and burn for example 1000 calories. At the end of it I'm completely knackered. I then start training hard. Six months later I then cycle the 20 miles again. Will I again burn 1000 calories because that is the energy required to travel that far on a bike, or as I become fitter does my body become more efficient and therefore may now only require 750 calories to do the same effort?

If your average power and duration for the ride is the same, yes, it would be about the same. It's not just about length/duration since conditions change (maintaining speed against a headwind will require more power for example). However, if you trained and are then much faster, you'll probably do the ride considerably faster since you can keep a higher average power for the same perceived effort. You'd then "win" calories burnt due to your now higher power, but also "lose" some since the duration of the ride would also be shortened.

sungod

as above, conditions will have a huge impact

with training, it's likely your weight will drop, which saves you energy on climbs, and probably reduces drag a bit, also it may result in your body becoming more efficient at burning fat, which may improve endurance

but if you are stronger/fitter/sleeker, you'll probably be going faster, the energy required to overcome drag rises exponentially, so it's quite possible you'll burn more energy for the same distance