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08/28/2010

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Nuno H Luz

Hi Joe,

Interesting post. One question related to this: even you're going 50+ mph, shouldn't you pedal anyway going downhill after a hard climb (and before another one) just to keep your legs moving/help recover/avoid the dead leg feel when you start the next climb?

Thanks in advance!

Nuno

Roger

Thanks for the post, I think it's very clear.

For those mathematically minded I would say that power increases polynomially with speed (to the power of 3) rather than exponentially. A 25% increase in speed represents a 95% increase in required power (1.25^3).

Joe Friel

Nuno--Turning the pedals easy or pedaling hard? big difference.

Nuno H Luz

Thanks for the reply, Joe.

I meant turning the pedals easy.

Nuno

Curt

Joe,

In earlier writings I think you recommended increasing power when riding into the wind. Why doesn't the same advice apply in that situation (i.e. reduce power into the wind and increase power with the wind at your back)?

Thank you for your blog. It is a great source of information.

Andy

Great info Joe as usual.

Side question: when is the best time to grab a drink of water/open up and pop a gel/eat some food. Is it best to do that while coasting down a hill or on a flat while doing some light pedaling? Which one wastes the least? thanks!

Joe Friel

Andy--The worst time to come out of an aero position is when going the fastest. That's nearly always downhill. The best time is when going the slowest. But that's usually a hard uphill when it is hard to drink or eat. That leaves the flat terrain.

Joe Friel

Curt--I think you may be misinterpreting or misremembering something I wrote. Into the wind in a steady state event such as a TT or tri power should remain constant while speed drops. Trying to maintain speed will require a greater output of power. Of course, there are still a few 'it depends' here. If it's a short period of time into a strong wind and it's a short race then it really won't be significant to raise power into the wind. Then we're talking about how strong of a wind vs how much power to overcome it.

Roberto

Dear Joe,

This is a very interesting post, as usual. I'm in a "college physics" doubt: Shouldn't it be considered the kinetic energy that depends on the squared speed?
Why do you use the speed to the third power?
Regards from Chile,

Roberto

Curt

My apologies. It wasn't your original work. You were quoting studies in your 17 Mar 2008 Blog that suggested increasing power into headwinds:

"* Using a mathematical model Swain found that when compared with a constant effort there was a significant time savings in a cycling time trial by slightly increasing power on the uphills and into headwinds and decreasing it slightly on downhills and with tailwinds. (Swain. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Med Sci Sports Exercise 29:1104-1108.)

* This study involved a review of other research such as Swain's above using a mathematical model to predict how hills and wind affect performance in a cycling time trial. The authors then revised the previous models slightly but the results were largely the same as the others: Increasing cycling power on uphills and decreasing it on downhills, and increasing power into the wind and decreasing it when riding with the wind improved time trial times significantly. (Atkinson et al. 2007. Variable versus constant power strategies during cycling time trials: prediction of time savings using an up-to-date mathematical model. J Sports Sci 25(9):1001-1009.)

* Seven male cyclists did a 16.1km (about 10 miles) time trial on a CompuTrainer 3 times each. There was a simulated 8km headwind in the first half of the ride and a simulated 8km tailwind in the second half. The pacing of the 3 rides were: a) self-selected pace, b) constant power and c) variable pacing with 5% higher power into the wind and self-selected and constant with the wind. Times were significantly faster in b and c compared with a. The fastest was c. Variable pacing based on power should be used when there is a headwind. (Atkinson and Brunskill. 2000. Pacing strategies during a cycling time trial with simulated headwinds and tailwinds. Ergonomics 43(10):1449-1460.)"

Applying the laws of fluid dynamics, it seems to me you would want to apply more power with a tailwind where you would get more speed per watt due to decreased drag.

Thanks.

Joe Friel

Roberto--Thanks for your note. When I wrote the piece I asked my physics buddy, Bill Cofer, for his input on the issue from a physics perspective. So I've asked him to reply to your comment. Here's his reply...

"Roberto is correct… Kinetic energy does depend on the speed squared. However, as speeds increase the energy used to overcome aero drag starts to become significant since aero drag is directly proportional to the velocity cubed."

Gary

Joe,

Thanks for the tips. Can you relate pedal easy and pedal steady to heart rate zones? After cresting a hill on a half iron course with virtually no flats, you know that you have recovered when .... ?

Joe Friel

Gary--Thanks for your comment. I really can't answer that. The part you're referring to came from Alan Couzens. You'd need to ask him how he interprets those instructions (you can probably reach him through his blog address which is listed in my blog). I'd take it to mean just back off some. No measured HR implied. Especially since HR is slow to respond. On a short downhill HR may not change at all even though you are coasting. Power would be a much better indicator since it is much more sensitive. Good luck!

Richard

Heya this is interesting principle, I always tried to keep pedalling at about 220 W (my ftp=330) below 50kmph, this year and found I was passing loads of people who would coast and then go far too hard up the next hill, after i while i was able ot pull away from them as they have spent more energy in the long term. So I agree that just keeping the pedals turning at a reasonable rate saved a great deal of time without much sacrifice of energy. I also used this principle for a couple of 50 and 100 mile TTs and found I could gain on other competitors whilst feeling like I was recovering.
So I definite agree with the idea.

Richard Sterry

Good post. A few months ago I did some number crunching for mountain biking that supports your theory.

If there is a downhill section of 1 mile, the time benefit of increasing your speed from 15-20mph is just 1 minute (increasing from 20-25mph will only gain 36 seconds over the mile). However, if there is an uphill section of 1 mile, the time benefit of increasing your speed from 3-4mph or from 4-6mph is a massive 5 minutes. This supports your theory to power up the hills and rest on the descents.

Applying this strategy for the South Downs Way in Southern England, I knocked off 1:30 hours from my personal best time for the 100 mile trail.

Supra Shoes

Good job.No matter where we are, we must study all the way. As the proverb says that: You are never too old to learn. Thank you for your blog.

Air Jordan

So nice blog! But I have a suggestion that you can add some humorous language up to your article. Maybe you can write more better.

Stuart Lynne

For TT's you should know what your average watts will be for the duration you will be racing. Then I follow two simple rules.

Get up to speed fast when starting downhill which may take a short anaerobic burst. Then generally use up to your average power while going downhill.

Possibly a little lower if conditions immediately ahead will require over your average watts (turning into the wind or uphill.)


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