TT pacing with powerTap

[mickthomas]

I have just started using my PT for TT pacing (I've set the rolling average to 5 sec). The area that concerns me is whether or not to include the start (say initial 20 seconds) as part of my pacing strategy. Lets say I'm aiming for a 315W average for a certain TT, the first 20-30 sec the average power is very high as I accelerate to get up to speed (since TTs start from a dead stop) leading to an iniitial high average - lets say 470W after 20 seconds. This could lead me to gradually backing off on the power till the average reduces to my pacing target and possibly losing time.

What is recommended as a strategy overcome this problem.

 

[Spunout]

Don't use average power in your display is the quick solution. You are using default watts display, right? Use 5 second averaging, good. In 5 seconds after you back off you'll be in your zone. Negligible performance hindrance.

If you wish to display average watts: You could get up to speed, back off to your target wattage and then advance the interval which would re-set the average display. Keep in mind that this also resets the KM or Time display but if you know your TT course this shouldn't cause a problem. (I do not think this is what you're thinking about though).

 

[frenchyge]

Shoot out of the gate, get in the right gear, drop into aero mode, take a breath or two, then look down. During that time (~15 secs or more) your initial power overshoot will have settled down and you should be near your target or approaching it quickly. If it's not, then you probably should back off slightly to keep it dropping towards the target.

20 secs at 470w seems like a pretty hot start for a target power of 315w.

 

[Spunout]

20 secs at 470w seems like a pretty hot start for a target power of 315w.

Agree, you aren't going to win a TT in the first 20s. But you can lose it

 

[RapDaddyo]

Depending on the course, the 1st 20s is the least of your pacing problems. It's not even clear if 315W should be your target power in the first minute or so. Is the course flat? If not flat, are there long climbs or just short rollers? What are the prevailing winds?

 

[padawan]

Depending on the course, the 1st 20s is the least of your pacing problems. It's not even clear if 315W should be your target power in the first minute or so. Is the course flat? If not flat, are there long climbs or just short rollers? What are the prevailing winds?

I agree that course layout and conditions play a huge factor in deciding my strategy for how I would use the PT display. I do triathlons (essentially, TTs) and I love using the PT for pacing. Sticking to a good wattage strategy is crucial because you have to have something in your legs to run afterwards.

If the course is flat and not too windy, you could just keep the power display on current power with 5 sec averaging and the 'other' display on cadence. Once you've figured out the correct gear for your self selected cadence that gets you around your target power output, you can just pedal and keep your eye on cadence and power every once in a while.

If dealing with hills or changing wind direction (much more common than a dead flat, no wind course), I start with the power on current display, just to make sure I don't hammer the start and switch it to average power display after a few km. That way the hills winds, etc. are taken into consideration. After that first few km when I switch over to average display, I'm looking to see that I am still a few watts under my target average. Start easy and build!

My $0.02
Pad

 

[mickthomas]

Depending on the course, the 1st 20s is the least of your pacing problems. It's not even clear if 315W should be your target power in the first minute or so. Is the course flat? If not flat, are there long climbs or just short rollers? What are the prevailing winds?

This was an 8:30 min effort up a 5% climb, although the first 800 m was flat. I wanted to average ~310 to 320W as I know I can hold that for 8 minutes. Looking at the graph afterward I had a relatively high power for the first 30 sec or minute (although it didn't feel that way and I probably would have over cooked it without the power meter) 450W for the first 30 seconds. Then I tried to back off and averaged 270W for the next 30 seconds as I tried to reach my wattage pace.

 

[RapDaddyo]

This was an 8:30 min effort up a 5% climb, although the first 800 m was flat. I wanted to average ~310 to 320W as I know I can hold that for 8 minutes. Looking at the graph afterward I had a relatively high power for the first 30 sec or minute (although it didn't feel that way and I probably would have over cooked it without the power meter) 450W for the first 30 seconds. Then I tried to back off and averaged 270W for the next 30 seconds as I tried to reach my wattage pace.

If the first 800 m was flat, then the optimal pacing strategy would have been to hold back until you got to the climb. I'm guessing that something like 250W for the first 800 m would be in the ballpark, maybe less! You get a much bigger payoff for increased power on the climb, especially if there is a section that is a bit steeper than the average grade. Plus, the greatest risk is overcooking it initially. If you wanted to ride that course for minimum time with a target of 315NP, you would probably ride the first 800m at ~250W and then ease it forward to ~300W when you started the climb and save your 300+W pushes for the slowest sections of the climb.

 

[SolarEnergy]

If the first 800 m was flat, then the optimal pacing strategy would have been to hold back until you got to the climb. I'm guessing that something like 250W for the first 800 m would be in the ballpark, maybe less! You get a much bigger payoff for increased power on the climb, especially if there is a section that is a bit steeper than the average grade.

You already explained this concept to me, with numbers to illustrate few examples, I was impressed and will use those knowledges every time they will apply. It had never crossed my mind that the return on power investment was so variable depending on the grade and the wind.

In this regard, you probably have a very good strategy.

But in this particular case, mine would rather involve starting the 800m at targeted ap, and stick to this number as soon as the climb section begins (~2min after the start signal). The first 800m would still feel like a walk in a park anyway.

My thinking is that 8:30min is a mostly VO2Max effort. High power aerobic capacity test. If the rider is properly rested, spending 2min well under pVO2Max may translate into lower average at the end, because it may be difficult to spend the remaining 6 min over pVO2Max without fatigue.

So basically, my strategy takes into consideration that acidosis would not be severe, and that the metabolical cost would not be that high, during the first 800m done at targeted ap.

At the end, maybe one minute from the finish line, I may even shift to max power display, and try to get the number moving.

 

[RapDaddyo]

My thinking is that 8:30min is a mostly VO2Max effort. High power aerobic capacity test. If the rider is properly rested, spending 2min well under pVO2Max may translate into lower average at the end, because it may be difficult to spend the remaining 6 min over pVO2Max without fatigue.

So basically, my strategy takes into consideration that acidosis would not be severe, and that the metabolical cost would not be that high, during the first 800m done at targeted ap.

At the end, maybe one minute from the finish line, I may even shift to max power display, and try to get the number moving.

The problem is that it all adds up. There just aren't any "free" watts at any point in the ride. If one can ride the first 30s at 450W and the last 8:00 at 315W, then he can ride the reverse strategy.

 

[SolarEnergy]

The problem is that it all adds up. There just aren't any "free" watts at any point in the ride. If one can ride the first 30s at 450W and the last 8:00 at 315W, then he can ride the reverse strategy.

I see.

Speaking about the first 30s, shouldn't the return on power investment be fairly high performance speaking(?), given that the body is accelerating from 0 to 40kmh? Also given that this duration will partly be done under atp-cp system, shouldn't it be done over targeted ap? Then maybe let the power drop down to targeted ap?

 

[Alex Simmons]

If you wish to display average watts: You could get up to speed, back off to your target wattage and then advance the interval which would re-set the average display. Keep in mind that this also resets the KM or Time display but if you know your TT course this shouldn't cause a problem. (I do not think this is what you're thinking about though).

Or hook up a 2nd harness and CPU

(just kidding) or an SRM with a revolving display

 

[RapDaddyo]

I see.

Speaking about the first 30s, shouldn't the return on power investment be fairly high performance speaking(?), given that the body is accelerating from 0 to 40kmh? Also given that this duration will partly be done under atp-cp system, shouldn't it be done over targeted ap? Then maybe let the power drop down to targeted ap?

But, it would take much less than 30s to accelerate to the optimal speed for this section of the course. As to drawing on a different energy system, that's true but that remains available later in the course as well. Just don't forget that part of AWC takes a long time to recover, way more than 8.5 mins. Use it now or use it later, but you can't use it now and use it later.

 

[SolarEnergy]

But, it would take much less than 30s to accelerate to the optimal speed for this section of the course

probably I take your guess more than mine

. As to drawing on a different energy system, that's true but that remains available later in the course as well. Just don't forget that part of AWC takes a long time to recover, way more than 8.5 mins. Use it now or use it later, but you can't use it now and use it later.

I may be wrong, but once depleted, I am not sure phosphocreatine energy system will be available per se anymore 'til few minutes after the end of the race, hence exploiting it during the first 30sec of the race.

I'd say the same principle is true for pure awc events. Better off giving more power at the beginin while being on a faster metabolical system, to get the body at race pace asap.

The part of AWC that takes long to recover, is the sever acidosis (that is still believed by some to cause fatigue). I think phosphocreatine system doesn't have much of a negative effect on acidosis.

 

[RapDaddyo]

I may be wrong, but once depleted, I am not sure phosphocreatine energy system will be available per se anymore 'til few minutes after the end of the race, hence exploiting it during the first 30sec of the race.

Let's say that a cyclist can ride for 30s at 450W and 8m at 315W. You're saying that he can't ride the reverse strategy, 8m at 315W and 30s at 450W?

 

[SolarEnergy]

Let's say that a cyclist can ride for 30s at 450W and 8m at 315W. You're saying that he can't ride the reverse strategy, 8m at 315W and 30s at 450W?

What I am saying is that the energy system on which you mostly relied in the first seconds of the race, is absolutely no longer available at the end of the race.

I might also add that if one can finish the last 30sec of an 8min race at 450 (targeted ap 315w or 340w whatever), one would have finished with this number anyway, even if begining the race with a 30sec at 450w.

You know, we're not talking about a lot of seconds here. I didn't calculate, but if I just try a guess, I'd expect maybe what, 5-10sec faster, if the first 800m is also done on average at targeted np. If not I don't see how you can catchup given that you'll spend most of the event at pVO2max (or near).

But maybe you're right too. That is just my strategy. Good thing to different riders have different strategies

 

[RapDaddyo]

I might also add that if one can finish the last 30sec of an 8min race at 450 (targeted ap 315w or 340w whatever), one would have finished with this number anyway, even if begining the race with a 30sec at 450w

No way. Not if the 315W was the max power for this duration. Try this experiment. Pick a power that you can ride for ~5mins max. By 5mins max, I mean that the last min is excruciatingly hard and you're counting the seconds until you can stop. Now get on your trainer and ride at that power for 4.5 mins and ride the last 30s at 150% of the target power. No way.

BTW, if you can ride the last 30s at 150%, then the target power was too low. You'll know when you have the right number because it will require 100% concentration to ride the last min.

 

[SolarEnergy]

No way. Not if the 315W was the max power for this duration.

Agreed.

I was just answering your question.
"Let's say that a cyclist can ride for 30s at 450W and 8m at 315W. You're saying that he can't ride the reverse strategy, 8m at 315W and 30s at 450W?"

I am just saying that the 450w at the begining and the one at the end are done on different fuel type. So if one's max ap is 315w over 8min, one can start at 450w without putting the 315 in 'danger' (sorry... what's the term jeoparty?). But, as you say, one would not necessarly be able to finish at 450w.

 

[RapDaddyo]

I am just saying that the 450w at the begining and the one at the end are done on different fuel type. So if one's max ap is 315w over 8min, one can start at 450w without putting the 315 in 'danger' (sorry... what's the term jeoparty?). But, as you say, one would not necessarly be able to finish at 450w.

That's exactly what I'm saying. If one can ride at 450W for 30s and 315W for 8m, then he can put the 450W effort at the beginning, middle or end. The question is where will he get the biggest benefit in time saved? The answer to that question is where he should put the 450W effort.

 

[SolarEnergy]

That's exactly what I'm saying. If one can ride at 450W for 30s and 315W for 8m, then he can put the 450W effort at the beginning, middle or end. The question is where will he get the biggest benefit in time saved? The answer to that question is where he should put the 450W effort.

Here RD. Yesterday night, I was discussion with you without looking at my reference books at all. I may have given the impression that atp-cp system could supply energy (at a very high rate) for 30 secs. That's not entirely true.

Though it may contribute for this duration, the supply will be at least half depleted after only 5-10sec after the start signal, as shown here in a little table adapted from Greenhaff and Timmons (1998).

I still stick to my strategy though, that is to push harder at the begining. Use this fast energy system while it's available to fight inertia from a short standing starts time trial event.

Energy comming from atp-cp system isn't availble at the end of a 8:30min effort done near pVO2Max, making it almost impossible to reach the same power numbers at the end of this event, without having to *under pace* the few minutes before the end.