Hello,

I beleive that a lot of the fitters measure power. Generally for tri, particularly longer events you want to maximize comfort, then power, then aero, then minimize weight. For a short tri you may be able to give up some comfort for more power or aero. Even without a power meter you can do some tests your self. Ideally you can find a 1-3 mile loop road in a park where you can ride laps all out. Ride multiple laps in different positions and record time Vs HR (or percieved exertion). Remember that HR may vary a little with a different position, more speed is what you ultimately want, not a lower HR, more watts, or more aero position.

OK, here is a more concrete question along the same lines: Have any of you who train with power found that a power meter has enabled you to make bike fit changes that create an immediate measurable ("free") improvement in your ability to generate power over a given distance at the same HR or RPE? If so, what changes did you make and how much improvement did it cause?

I don't have any first hand experience with power/aero tweaking yet. But I spent a day riding with a chap who commented that "once you ride with a power meter and see the effect of position on power output, you'll never go back to riding without power measurement" (or something like that). Up until that point, I had ruled out the idea of including a power meter simply based on the price. His comment was enough to convince me to spec an Ergomo on my new bike. So the short answer to your question is "Yes - power has allowed at least one person to improve their bike fit, but I don't know the specifics of his changes".

Rob

Normally what I have done is set my saddle height and fore/aft according to slowmans articles or by feel. Then I start out with the aerobars set as low as possible and as narrow as possible (which is typically very aero).

Next I do a series of hard 15 minute intervals (on a trainer) with full recovery in between, measuring HR, power and cadence using a powertap. In between I raise and/or widen the aerobars. Generally, the power and comfort will go up. When power stops going up significantly, their you are.

This should be repeated a few times to take drift and fitness into account. Also it should be done every year as fitness and flexibility changes.

Also note that the saddle tilt and height might need to be changed as the aerobar height is changed.

Most fitters that I have heard of use your bike and a computrainer. I would love to see a powermeter attached to a serotta size cycle (very adjustable) to get your ideal position. Then you would need to find which frame best accomadates that position.

"measuring power output in different positions at a constant heartrate? Is this a valid exercise?"

you have to be careful with this. let's consider cadence instead of position, and let's say you fix the wattage and pit cadence against HR. at a very lower power output the exercise works. but at a higher effort level, you'll find that the most (aerobically) economical cadence is about 70rpm.

however, you'll be better off at 90rpm than at 70rpm, and the reason is that your aerobic system is not the only system you need to accommodate. you might burn less O2 at 70rpm, but if you're exhausting your thigh muscles of glycogen because of the bigger gear you're mashing, you can't easily recover from that later in the ride, or during the run.

you must keep that in mind when considering using this test. i guess i'd say that it's a reasonably valid test if, and only if, you eliminate cadence as a variable, by keeping your cadence the same, and relatively high, during each test.

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Dan Empfield
aka Slowman

I believe that this is not a valid exercise, due to the lack of adaptation for any given position. In other words, it may be possible to generate more power at lower cost in a new position, but only after the body has adapted to that new position, and that won't happen on a test ride. If there is something grossly wrong with your position (like you are riding with your stomach on the saddle), you might see some immediate results.

Ken Lehner

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"Go yell at an M&M"

Dan wrote: "however, you'll be better off at 90rpm than at 70rpm, and the reason is that your aerobic system is not the only system you need to accommodate. you might burn less O2 at 70rpm, but if you're exhausting your thigh muscles of glycogen because of the bigger gear you're mashing, you can't easily recover from that later in the ride, or during the run."

while one might burn more glycogen per stroke at a lower RPM I don't think it has ever been extablished that more glycogen is burned per unit time, at the same power, especially if the O2 burned is less (efficiency is greater), at lower cadence.

I think this is simply untested lore to justify peoples bias. You might be right but it makes little sense physiologically.

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Frank,
An original Ironman and the Inventor of PowerCranks

"I don't think it has ever been extablished that more glycogen is burned per unit time, at the same power, especially if the O2 burned is less (efficiency is greater), at lower cadence."

Ahlquist, et al, “The effect of pedaling frequency on glycogen depletion rates in type I and type II quadriceps muscle fibers during submaximal cycling exercise.” (European Journal of Applied Physiology, 1992:65)

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Dan Empfield
aka Slowman

there is a fitter here in St. Augustine, Fl. that will fit you using power, HR ect. (possibly with a computrainer) I think it costs about $300.

AND

All else being equal...

O2 demand (and therefore for the most part HR) will be less as the shift is made to a greater reliance on glycogen over lipids.

“The effect of pedaling frequency on glycogen depletion rates in type I and type II quadriceps muscle fibers during submaximal cycling exercise.” (European Journal of Applied Physiology, 1992:65)

Is that available without going to the medical library. I would like to read it. Makes no sense to me as to why this should be the case.

Frank

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Frank,
An original Ironman and the Inventor of PowerCranks

"Is that available without going to the medical library. I would like to read it. Makes no sense to me as to why this should be the case."

cost me $17 or $20 online. do a pubmed search and they'll show you how to pay the money and download the pdf. i'd email it to you but i don't know if i can find it. i'll look.

what has been demonstrated for decades is that 60rpm to 70rpm is the most economical cadence (if economy = O2 consumption) but cyclists both in the lab and on the road routinely choose a much higher cadence when given the option. why is that?

ahlquist measured glycogen depletion in the thigh muscles at various cadences. that rather (in my mind) landmark study answered the question. the mechanism is as follows:

1. at higher cadence rates less torque is applied per revolution, and fiber recruitment is limited to slow twitch fibers plus fewer (if any) recruitment of fast twitch fibers.

2. lower cadence rates result in a recruitment of a greater number of fast twitch fibers in order to do the work. since these fibers consume glycogen at a rate 50% higher than ST fibers, glycogen depletion is correspondingly increased.

3. therefore, the neuromuscular cost of a lower cadence overshadows the less economical nature of a higher cadence, that is, yes, you'll ride with a HR a couple of beats higher because of your faster cadence, but you won't blow your legs up.

one may or may not buy ahlquist's analysis, or his methodology (whatever) but i think the reasoning is sound on its face, and it parallels what is found in practice among cyclists.

i like to use the analogy of weight lifting. here's an event for you: bench press 2000 lb and then do 50 pushups. first guy to finish wins. bench press the 2000 lb however you wish. 50 x 40 lb, or 10 x 200 lb. you choose. just remember that you've got 50 pushups to do after it's over.

yes, you might be the first guy to finish the bench pressing if you choose 10 x 200 lb, and your HR might be lower than the guy who did 40 reps of 50 pounds, but will you have enough left over to finish off the 50 push ups, or will you have blown up your arms?

the "50 push ups" relates to whatever you need to do at the end of your event. for lance, it's the last 10km climb of a mountaintop tour stage, for you and me its the 10km or 13mi run. either way, a faster cadence gets us to the finish line first.

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Dan Empfield
aka Slowman

Can anyone provide an example of how a most 'comfortable' position would not also provide the most sustainable power (not short term power - sustainable power)?

It's my belief that for the most part 'comfort = sustainable power'. The tradeoff between aerodynamics and comfort is pretty much the same as the tradeoff between aerodynamics and sustainable power.

Dan wrote: "1. at higher cadence rates less torque is applied per revolution, and fiber recruitment is limited to slow twitch fibers plus fewer (if any) recruitment of fast twitch fibers.

2. lower cadence rates result in a recruitment of a greater number of fast twitch fibers in order to do the work. since these fibers consume glycogen at a rate 50% higher than ST fibers, glycogen depletion is correspondingly increased.

3. therefore, the neuromuscular cost of a lower cadence overshadows the less economical nature of a higher cadence, that is, yes, you'll ride with a HR a couple of beats higher because of your faster cadence, but you won't blow your legs up.

one may or may not buy ahlquist's analysis, or his methodology (whatever) but i think the reasoning is sound on its face, and it parallels what is found in practice among cyclists. "

here is my problem with such an analysis.

I agree that fast twitch muscles deplete glycogen faster than slow twitch muscles. However, faster cadences do not necessarily mean fewer fast twitch muscle recruitment even though there is less force put on the pedal for any given power at higher cadences. Why, because, before one can put one ounce of force on the pedal one must get the foot up to the speed and in the direction of the pedal. The only way to do this is through muscular action, the same muscles that put force on the pedal.

If Ahlquist had also measured intramuscular pressure he would have found that intramuscular pressure went up with both higher and lower cadences. There is an optimum cadence for any given power. This probably correlates closely to the optimum efficiency. Otherwise we would follow this reasoning and all ride at a cadence of 150 or 175. Try riding at a cadence of 150 (even at low power) and see how long your glycogen lasts. Did Ahlquist also measure efficiency and coorelate it to glycogen depetion? The higher the power the higher this optimum cadence.

Pros, who put out higher powers have optimum cadences higher than amateurs whose power output is a lot less. Amateurs who mimick pros are wasting energy and wasting glycogen, in my humble opinion.

To use this paper to advocate that everyone should ride at high cadences misinterprets the data I believe.

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Frank,
An original Ironman and the Inventor of PowerCranks

I think the primary reason road racers use smaller gears in road races is that it is much easier to tolerate accelerations.
if everyone is on a 53-15, spinning 100rpm and you are on a 56x13 at 65rpm, as soon as someone accelerates, you are history...see Ulrich in TdF 2 years ago, pushing much bigger gears than Lance...
this year he was pushing slightly smaller a was able to react (not always though, but that's an other issue)

"Didn't you once brag that you'd put your knowledge of exercise physiology up against anybody's"

I think I did, although I may have meant physiology and not exercise physiology, per se. I am, after, all, an anesthesiolgist. An anesthesiolgists job is to understand physiology and get oxygen to the cells under all sorts of adverse circumstances in a manner not to cause harm. I was also a trained nuclear engineer before i went into medicine so I have a pretty good understanding of mechanical priciples. At one time I was also a retty good athlete but never elite. Now, it has been awhile since I did that stuff serously so I am probably not as knowledgeable as I once was but I have a pretty good grasp on this stuff, yes.

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Frank,
An original Ironman and the Inventor of PowerCranks

"orrelates, maybe, but the two are definitely not the same."

Why are you so definite about this?

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Frank,
An original Ironman and the Inventor of PowerCranks

I accept that under certain tactical race conditions that athletes can accept less efficiency to gain other advantages, such as increaased acceleration. Higher power requires higher cadences. High acceleration requires high power.

What we are talking about here (power, efficiency and glycogen depletion) has primary applicability to TT's and triathlons. Even under these conditions athletes must accelerate out of corners, etc. Of course, isn't that what the gears are for, something to allow you to rapidly change cadence for acceleration, if you need to.

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Frank,
An original Ironman and the Inventor of PowerCranks

I just don't believe the studies are there to support this interpretation. Simply because an author opines that a certain mechanism explains the results, doesn't make it so as there could also be other explanations or mechanisms that are just as valid. Under those circumstances the researcher should design a study to try to figure out which is the best one.
Frank

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Frank,
An original Ironman and the Inventor of PowerCranks

"However, faster cadences do not necessarily mean fewer fast twitch muscle recruitment"

my reason for bringing this up was only to apprise you of a study that you didn't know existed.

there are plenty of studies that reference cadence, dozens that i've read. ahlquist is the most intriguing, tho, in that he seems to tackle the question of, "why is it that all accomplished cyclists -- other than ultradistance riders -- almost without exception favor a cadence 20 beats higher than is optimal for O2 consumption?"

btw, unrelated, but i don't see that any of this argues against the use of the PC. perhaps it even argues more in favor of it.

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Dan Empfield
aka Slowman

"I think the primary reason road racers use smaller gears in road races is that it is much easier to tolerate accelerations."

that explains crits or "crit-like road races" but not, imho, long road courses, especially hilly ones. fresher, fitter riders climb with higher cadences. your cadence drops, you're toast. even if nobody is around you.

likewise on flats, even if you're alone. the longer the event, however, the less torque applied, the less fast twitch fiber recruitment (hence a lesser problem of neuromuscular fatigue) and the more the aerobic needs must be considered (hence a correspondingly slower cadence).

there is no perfect cadence. there is just an appropriate gradient, or line, that describes the relationship between cadence and event distance.

as to your very true statement about tactics, a cadence of 120rpm is quite common in crits, but that's not what we're talking about here i don't think.

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Dan Empfield
aka Slowman