Slightly off topic, but we are off topic anyway: I would be very curious to learn about the relationship between caloric intake, mechanical power output, and power consumption.

In simpler terms, if I eat 1000 Calories, then go on a ride during which I average 100 Watts for one hour, how many of those 1000 Calories do I burn? Surely it must be a lot higher than the actual measured energy output of 100 Watts for an hour (equates to 360000 J = 90 Calories) , since the body is not perfectly efficient. It also must be a function of how well your body is fitted to the bike, and probably somehow related to fitness level.

I already know the rule of thumb 40 Calories per mile, but I am interested in a more meaningful relationship. If this rule of thumb is true it seems to me the body must only be about 16% efficient at converting stored energy to torque at the crankshaft!

To get a 100% accurate you will have to measure it in a lab using expired gas analysis. Its the same equipment they use to measure VO2Max. Essentially your calories burned is proportional to the ratio of O2 consumed Vs CO2 put out.

You are correct, the mechanical power does not account for cycling efficiency, and this is different for every individual person.

A good way of estimating it is to use a heart rate monitor. The calorie expenditure algorithms in the Polar (probably others too, but I haven't tested them) monitors are quite good. I have tested this in a lab myself and my polar monitor was bang on with my readings from indirect calorimetry (gas method). I emailed polar after doing that experiment and got a fairly technical but very good reply from them on how they created the formulas, basically in my opinion they are quite a good estimation, but will not be 100% perfect for everyone.

Anyway, the calories burned as stated by your heartrate monitor should be a good representation of true calories burned, if you have a power meter on your bike you can measure the mechanical work done and estimate efficiency.

Il Pirata, not only did hill climbing patrick, that was his strong point, but he and all the other riders on the peloton had to do also long flat runs all year long.

We are talking about recreational cyclists who chose to do mostly flats compared to mostly hills.

Wow great information. Do you know what formula they use? My cycle computer has a heart rate monitor but no estimation of Calories burnt. I think it must depend on your heart size (volume pumped per heart beat) as well, shouldn't it? Which would be difficult to know without the lab experiment?

Essentially what they did is got a few groups of people all of different fitness/activity levels and got them to do an exercise protocol with HRM's and gas analysis. They were able to them make regression formulas based on the different groups to calculate energy expenditure based on heartrate. As far as I know the formula's are propriety, but some time when I get a chance I might try looking for them in the sports science literature just in case they did get published somewhere. I know that they did refer me to two articles at the time. I'll have to see if I still have the email from them.

Efficiency will be related to many things. There will be physiological, biomechanical and kinematic aspects to it. This is where the balance between aerodynamics and ability to maintain power output comes in on the time trial discussion earlier. Essentially you have an Oxygen uptake chain, how much Oxygen can get into the lungs, how much can be perfused into the blood, how much can be stored by the blood, how much blood the heart can pump, how much the muscle can take out of the blood. An inefficiency anywhere on this chain will reduce cycling efficiency. Poor biomechanics can mean that you get less power into the pedals for a given oxygen uptake too. Its fairly complicated, but just goes to show that there are many aspects that can be trained to make you a more efficient cyclist.

and

sounds interesting, but I keep all math and science for my work hours, kthx

Now, how about the weekend ?

This is total crap, equal time spent climbing hills or on the flat, you will burn more calories and thus lose more weight climbing hills. Of course, that means you actually have to climb the hills on your bike not walk up or turn around half and call it a day.

But it is work hours

Hill climbing happens closer to your anaerobic threshold, hence burning less fat per equal effort in the same time.

a 1 hour hill climbing session will not burn the same fat as 1 hour flat riding, you'll build more muscle on the climb but you'll be less tired and leaner when doing the flat.

Easy aerobic exercise vs Hard anaerobic exercise.

None is "better" or "superior" to the other, simply they serve different purposes, and now I have 6Kg to burn, so I'll do more flats

Thanks for sticking your neck out, Salsa. I was on the verge of doing that myself. My concerns are
1. So much nerdy (and useful, priceless info) is getting lost deep down a different thread; I would have loved if all this info could be cross-linked to some great info threads Chris and others have posted about cycling.

2. My immediate worry is we are not a step closer to resolving where we are headed this weekend. We need to plan/prepare for it

I think everyone interested has decided to go around the lake on Saturday? correct?

Pity, I sold the 50cm Trek 5200 I had, some months ago.

I do have a bike that could fit you but I don't know if it would be good for the weekend for you

it is a bike with 650c wheels, has downtube shifters and is not heavy and very stiff ( made of Metamic B2C alloy )

If you want to check it out you can borrow it for the rides. it has standard pedals, downtube shifters, 2x8 gears, and standard road handlebars .

I'm in, let's see if Nathu can also do it on Sat, he was proposing Sunday.

Ah I missed that. I can do either day. If we do Sunday, I will still do the Oerlikon ride on Saturday.

You have just showed a total lack of understanding of how the body works.

Riding at threshold (or over) does not result in you burning less fat! The percentage of fat you burn reduces. This is not because you burn less fat but because you start to use more glycogen as an energy source. The absoulte level of fat burned does not drop. Furthermore its still all calories burned and at the end of the day creates a calorie deficit which is what is most important for weight loss... not the type of fuel you use.

As for the Oxford thing you quoted, that is out of context and is more an explanation of interval training. Lactate levels or tolerance to lactate do not change that much with training. What changes is power output and heartrate at threshold. Threshold for nearly everyone if 4mM of lactate in the blood. Some people with high tolerance may be able to have more, but generally this figure does not change that much. What changes is the power output and heartrate that someone has with a lactate concentration of 4mM. The reason that this is threshold is because over this the body does not use the same amount of lactate as it produces. Lactate is also a fuel and us used to generate power, its just that as the intensity increases the production increases, but the amount that can be used as a fuel is limited.

whatever.... I'll be doing my flats this weekend with anyone who wants to join....

you can stay at the library if you wish

So why can't one of you freeze it, by posting a new thread with (up)dated title? Since Patrick was the first to post a firm event (oerlikon, Sat) in this thread, my suggestion is, let's do that on Sat and keep the other event for Sunday.

I am up for both.

It's more objective than you realise:

Zurichsee is surrounded by hills.

The sides of these hills and the air around them are heated by the sun but the lake stays relatively cool.

The hot air rises up the hill sides (and is normally triggered into a thermal at the top of the ridge).

But, if all this air is rising up on the hills around the lake, air must be rushing in to take its place.
This air comes from from the lake (or appears to at ground level).
Additionally, as this air is cooler, the breeze feels stronger.

All this is more apparent during the spring / summer cycling season when the sun is highest and warmer, and so heats all hillsides.

It's not the library... or at least not now. This is the stuff my degree is in.

That is very nice of you We take it further by pm?