Time Trial by power

koger

Hello

I'm looking for some info about time trial by power.
My first theory is that I should keep the power output at a fixed point relative to FTP depending on the length/expected duration of the route.
On second thought, it might not be so simple as the route could be hilly and the wind may change.

Hills - the slower I ride, the less energy (than average) I'm going to waste on breaking the wind. So my conclusion is that I should spend more energy going uphill than when riding on the flats.

Wind - the same goes for wind. I should spend more energy when having headwind and less in the tailwind.
This also means that I should spend less energy when going downhill.

Does this make sense to you - and if it does, how much more or less energy should I at the different parts of the route?

beerco

You pretty much have it. If you search this site there are some discussions in the archives. Just make sure you don't go so hard that you pop during the "hard" portions.

daveryanwyoming

Both your theories are good depending on the course and the conditions. But basically you should be trying to hold your best average power for the duration. On a rolling course or one with a lot of wind changes you should do as you suggest, work a bit harder into the winds and uphill but overall you're still targeting your best estimated sustainable power for the duration. That means the hard sections can't be much harder than that average and you shouldn't back off too much in the "easier" sections. You shouldn't for instance, coast on gentle descents and try to make it up by killing the hills you're still bounded by AP(and NP) for the duration so don't stray too far from that average.

Perhaps the most important way to use a PM during a TT is to keep one eye on the meter for the first five minutes or so to make sure you're not going out too hard in the excitement. If you can stay at or slightly below your best AP for the duration during those opening minutes you're in a much better position to just listen to your body and pace accordingly for the rest of the effort. If you go out too hard(really common problem with race day excitement) it'll be really tough to pace later on when it really counts.

Good luck,
-Dave

dkrenik

Your plan is pretty sound. Do as Beerco recommends and search the archives (try "variable pacing strategy").

One area that I think you need to look at again is:

When you think about it, I believe that you'll want to do the opposite. The logic is similar for why you would want to lift your effort (wrt FTP) on uphill sections vs downhill sections. You get more bang for your buck when you can limit the % of effort used to overcome wind resistance - if I got that right.

Dave

frenchyge

Not exactly. It doesn't matter whether the resistance is wind, gravity, or rolling friction, but you'll get the best bang for your energy use whenever there's a lot of 'it' (ie, resistance).

One way to think about it is that the baseline for comparison would be an isopower output. The isopower rider is going to lose a lot more speed when the resistance is high than they gain when the resistance is lower. Now, think about how a variable power approach could be constructed to minimize that effect and you'll see that it's best to go hard during the slow sections of the course and cruise during the fast sections.

rmur17

mantra: when you start to slow down, push harder

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rmur

koger

Thanks for your replies, and for the tip on searching the archive. There are some great posts.

The biggest problem, I still haven't found a solution to is how harder or easier should I go, on the different parts of the course. It seems almost impossible to answer that, since there are a lot of variables. The gradient, the wind velocity, length of the various course parts, my physics e.g. I know the avg. power, but if I take I go say 20w easier for 1 minute, how much harder can I climb the hill without blowing on the way home.

Calculating it seems impossible, so I guess the best thing is to have some good rule of thumps.

acoggan

Actually, it's pretty easy - the hard part is executing such an optimal (theoretically, anyway) pacing strategy "on the fly". I therefore view such endeavors as simply a way to get in the ballpark, with further refinement coming from experience and/or pre-riding the course in question.

koger

lAny rule of thumb where I could start, say go 5% slower on flat a couple of miles before the hill, then 10% harder up the hill - or something like that

It's not easy getting experience in the real world. I have to be equally rested, the wind conditions have to be the same for me to compare two tests. I really don't see how I can get the correct experience.

Markster

Anecdotally, I hear more and more (educated and respected riders) advocating a constant power approach. I think Chris Boardman did this. In my own experience I also seem to have achieved better results/watt when aiming to hold a constant power.

Could it be that as soon as you consciously attempt to ride to a variable schedule, you introduce too much variance. i.e. with the best will in the world you tend to vary a fair bit anyway in anything other than a flat straight windless course. Aiming to vary more on top of that then puts you too far either side of threshold, and you end up putting less actual J's into the system (even if you are applying them a bit more efficiently).

Alex Simmons

Since we naturally push harder up hill and into a headwind, I suspect it's more to do with how much one should hold back their effort on climbs/headwinds than looking to encourage them to push even harder.

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robkit

i dont have anything like the real numbers or explaination of the physiological principles that demonstrate this right now, but i beleive i read something stating that it takes your body 4 times as long to recover from a unit of power generated above threshold than it does for power generated within.

seemingly this would support the idea that the greatest energy release over a distance is actually achieved by riding at a constant power equal to or very close to your threshold power.

putting it more simply this is equal to the way i have always ridden time trials...bumping HR upto and off threshold but maybe going over by 2-5 beats on a drag or hill.

probably the biggest contribution of power meters in time trialling is in ensuring you dont go way too hard in the first few minutes... i rode my first TT with an SRM a coulple of weeks ago and even with this firmly in mind i was amazed how much excess power i wanted to put out from the start line.

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Alex Simmons

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Alex Simmons

These abstracts might prove an interesting read:

http://www.ncbi.nlm.nih.gov/pubmed/...ed_Discovery_RA

http://www.ncbi.nlm.nih.gov/pubmed/...ed_Discovery_RA

http://www.ncbi.nlm.nih.gov/pubmed/...ed_Discovery_RA

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