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Fit and Watts Question to assess whether difference is significant

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Fit and Watts Question to assess whether difference is significant

Old 11-29-08, 09:40 PM
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bostongarden
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Fit and Watts Question to assess whether difference is significant

Santa came early...mother-in-law asked what I wanted...so, what the hey, why not a fit...anyway, phase one of the process involved sitting on a Calfee adjustable stationary bike hooked up to a computer that made a lot of measurements based on some electronic-based flywheel in the back.

I'm curious whether anything can be made of difference in watts given my original position and an "initial" new position -- also, I don't know whether the info I provide enables you to assess this...but, I am curious.

I rode for 5 minutes on a 2.5% grade in a 40/21 at an average rpm/cadence of 85 (that's what I was told to do, so, that's what I did)...with my "original" settings, the (average I believe) watts were 181...with the "initial" new position, the (again, I believe average) watts were 177. [Note that average rpm, average speed, and distance covered were identical for both 5 minute periods...if I understand this correctly, with the "initial" new position, it took 177 watts of energy, rather than 181 with my "original" position, for me to go the same distance at the same average speed].

Let's put aside that I have no other sample data. Is such a difference in watts significant? Is this even possible to assess given the information provided?

Thank you Power-Measurement Gurus!!
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Old 11-29-08, 09:54 PM
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its impossible to do the same distance/speed with less watts.. unless you are more aero... and I doubt they were simulating that..

I dont really understand the reasoning behind that test... I think they should let you pick your gear/cadence instead of telling you what to do...
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Old 11-29-08, 11:37 PM
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Um, yeah, what dmotoguy said, that doesn't make any sense. If you were on a stationary bike and had the same resistance, gear, cadence, speed, distance, etc. were all the same the power has to be the same, regardless of your position. The only thing the position can affect is your aerodynamics or your ability to produce power, e.g. a lower position may make it more difficult to get sufficient oxygen, or have a hip angle that is more limiting...
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Old 11-30-08, 07:26 AM
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Thanks for the replies.

A couple of things:

1) for the moment, let's put aside whether this makes sense; I'll change the question: suppose a change could be made such that one would use 177 watts rather than 181 watts when cycling from point a to point b on a 2.5% grade in 5 minutes. Is the difference in watts significant/meaningful? Were you to get this difference, would you think it was a big deal, a somewhat big deal or no big deal at all?

2) Couldn't pedaling/stroke efficiency affect power requirement in watts? That is, perhaps, relatively speaking, my pedaling stroke was smoother in the second run. Wouldn't that affect energy requirements? Think about it. Consider 2 cyclists, KO and KI. KO pedals with his knees pointing out to the side (i.e., pretty inefficient) and KI pedals with his knees straight up and down over the pedals (i.e., pretty efficient -- if you prefer to say over the crank-arms, that's fine too...but, let's assume clearly that KI pedals with more efficiency). So, they are riding together from point A to point B. They are each in the same gear; they are each pedaling with the same rpm/cadence; they ride next to each other the whole way from point A to point B such that their distance covered is the same and their average speed is the same (and again, the average cadence was the same). Do you believe that KO -- who again is pedaling with a less efficient stroke technique -- had to generate more energy than KI to cover the same distance in the same length of time with the same cadence? If you answered yes , would you please indicate whether 177 watts vs 181 watts in my scenario was material, i.e., would you care if you were able to realize this change in your energy use?
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Old 11-30-08, 08:00 AM
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Originally Posted by bostongarden View Post
2) Couldn't pedaling/stroke efficiency affect power requirement in watts? That is, perhaps, relatively speaking, my pedaling stroke was smoother in the second run. Wouldn't that affect energy requirements? Think about it. Consider 2 cyclists, KO and KI. KO pedals with his knees pointing out to the side (i.e., pretty inefficient) and KI pedals with his knees straight up and down over the pedals (i.e., pretty efficient -- if you prefer to say over the crank-arms, that's fine too...but, let's assume clearly that KI pedals with more efficiency). So, they are riding together from point A to point B. They are each in the same gear; they are each pedaling with the same rpm/cadence; they ride next to each other the whole way from point A to point B such that their distance covered is the same and their average speed is the same (and again, the average cadence was the same). Do you believe that KO -- who again is pedaling with a less efficient stroke technique -- had to generate more energy than KI to cover the same distance in the same length of time with the same cadence? If you answered yes , would you please indicate whether 177 watts vs 181 watts in my scenario was material, i.e., would you care if you were able to realize this change in your energy use?
First of all, you're using efficiency wrong. Efficiency refers thermodynamics, not mechanics. Where you write efficient, replace it with fast; inefficient with slow. Second, smooth pedaling has nothing to do with going faster, and may, in fact, be slower. http://www.midweekclub.ca/articles/coyle91.pdf For your example though, the effect of pedaling with knees out would be to increase aerodynamic drag; knees out projecting more area to the wind. As to whether a 4 W difference would be significant, that depends on each individual. You can work it out for yourself here: http://www.analyticcycling.com
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Old 11-30-08, 08:18 AM
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The salient is being missed:

It's a stationary bike. You are not moving. You pedaled for 5 minutes at the same RPM. You generated 4w less power in the "new" position.

You went backwards. Figuratively of course.
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Old 11-30-08, 08:31 AM
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One more point: you can't compare power values until your body gets used to the new position, which could take a few weeks. By then your power will have changed anyway, so you really just can't compare accurately.
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Old 11-30-08, 09:07 AM
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I gotta go against the grain here and disagree with everyone else.

Imagine you only use 10% of each pedal stroke to propel the bike forward, with the remaining 90% adding no energy.

You would accelerate the bike forward for that 10%, then the bike begins decelerating until the other foot pushes down where you begin accelerating again for 10% and then decelerating again.

Essentially you're accelerating 20% of the time and decelerating 80%. The steeper the grade, the more noticeable this is, I'm sure you've noticed something not as drastic when climbing out of the saddle on a steep road, especially next to another rider for a relative comparison.

What the computer is telling you is that you went from adding energy to the pedal stroke X% of the time to X+Y% to go the same speed up a hill.

The new fit has increased the smoothness of your pedal stroke, allowing you to climb slightly better.

This was not watts for a given PE or HR or time, but simply watts to go up a hill at a given speed.
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Old 11-30-08, 09:13 AM
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Originally Posted by Hocam View Post
I gotta go against the grain here and disagree with everyone else.

Imagine you only use 10% of each pedal stroke to propel the bike forward, with the remaining 90% adding no energy. ...
Before you go disagreeing, how about showing us the data? Coyle et al published 17 years ago and as far as I know, no one has produced data contradicting theirs. If you know something the rest of us don't, how about sharing.
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Old 11-30-08, 09:22 AM
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This sounds like that fuzzy math.
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Old 11-30-08, 09:43 AM
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Originally Posted by Hocam View Post
I gotta go against the grain here and disagree with everyone else.

Imagine you only use 10% of each pedal stroke to propel the bike forward, with the remaining 90% adding no energy.

You would accelerate the bike forward for that 10%, then the bike begins decelerating until the other foot pushes down where you begin accelerating again for 10% and then decelerating again.

Essentially you're accelerating 20% of the time and decelerating 80%. The steeper the grade, the more noticeable this is, I'm sure you've noticed something not as drastic when climbing out of the saddle on a steep road, especially next to another rider for a relative comparison.

What the computer is telling you is that you went from adding energy to the pedal stroke X% of the time to X+Y% to go the same speed up a hill.

The new fit has increased the smoothness of your pedal stroke, allowing you to climb slightly better.

This was not watts for a given PE or HR or time, but simply watts to go up a hill at a given speed.
I suppose that's possible but I'm not entirely convinced...
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Old 11-30-08, 10:52 AM
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Originally Posted by Hocam View Post
I gotta go against the grain here and disagree with everyone else.

Imagine you only use 10% of each pedal stroke to propel the bike forward, with the remaining 90% adding no energy.

What the computer is telling you is that you went from adding energy to the pedal stroke X% of the time to X+Y% to go the same speed up a hill.

The new fit has increased the smoothness of your pedal stroke, allowing you to climb slightly better.

This was not watts for a given PE or HR or time, but simply watts to go up a hill at a given speed.
If you go from making power 20% of the time to making power 20+X% of the time, your average power should go up. His avg. power went down.

that's why power is so great. It tells you how hard you're working. Peroid. the only unaccounted for variables are physical exertion (maybe 177W felt WAY easier than 181W) and aerodynamics, which aren't accounted for in a bike shop fit, esp on a simulated hill.
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Old 11-30-08, 11:13 AM
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Originally Posted by asgelle View Post
Before you go disagreeing, how about showing us the data? Coyle et al published 17 years ago and as far as I know, no one has produced data contradicting theirs. If you know something the rest of us don't, how about sharing.
The article you posted showed a correlation between elite national races being faster than competitive riders during a 40k TT done indoors because of these reasons:

1. Elite riders were operating at a higher % of VO2 max
2. Elite riders had denser muscle fibers and more type 1 fibers
3. Elite riders were producing more vertical torque during the pedal stroke

The riders in the article were riding a trainer at a given wattage simulating flat terrain, where aerodynamic drag is the biggest force the rider is resisting.

I was talking about climbing a hill, where gravity plays the biggest force the rider is resisting.

Why do you assume that one paper covers all cases? Also, wouldn't reason 3 be due to reason 2?

When you use analytic cycling, it's calculating the steady-state power to go up that hill, but you do not produce power in a steady state manner. Analytic cycling's number is the minimum power to go up a given hill at a given speed.

If you climb a steep hill, standing on the gears and pushing down very hard, your speed vs. time graph would be something like a sin wave, with peaks and valleys. You're constantly accelerating during the power phase of your pedal stroke and slowing down between power phases, then re-accelerating to the same speed. To accelerate a mass takes energy, so you're losing energy both from going up the hill and accelerating yourself.

So, if you reduce the amount you're decelerating due to changes in applied power from your pedal stroke, it takes less energy to go up the hill.

Doesn't sound fuzzy to me.

Last edited by Hocam; 11-30-08 at 11:19 AM.
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Old 11-30-08, 11:18 AM
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Originally Posted by brianappleby View Post
If you go from making power 20% of the time to making power 20+X% of the time, your average power should go up. His avg. power went down.

that's why power is so great. It tells you how hard you're working. Peroid. the only unaccounted for variables are physical exertion (maybe 177W felt WAY easier than 181W) and aerodynamics, which aren't accounted for in a bike shop fit, esp on a simulated hill.
You're misinterpreting what I mean, let me try to be clearer.

Keep the amount of work done during a pedal stroke constant (kJ), and the cadence constant (RPM), then the power is constant (Watts).

However, the rate power applied is not constant during your pedal stroke. If you go from applying power 20% of the time to 30% of the time, your peak power is lower but average power remains the same.

In the case of a more even pedal stroke, the OP's case, gravity is decelerating you for a smaller amount of time, so you need slightly less power to go up a given grade at a given speed and cadence.

Last edited by Hocam; 11-30-08 at 11:21 AM.
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Old 11-30-08, 11:40 AM
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and none of this matters because it still takes the same amount of watts to get from point A to point B, if nothing changes... yes you can have a smoother pedal stroke, thats great, but you will still need the same average watts...

without knowing more about the setup that the op was tested on, i would say that the 4 watt difference doesnt mean anything at all.
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Old 11-30-08, 11:41 AM
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Originally Posted by Hocam View Post
gravity is decelerating you for a smaller amount of time, so you need slightly less power to go up a given grade at a given speed and cadence.
gravity is constant
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Old 11-30-08, 11:47 AM
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Originally Posted by Hocam View Post
In the case of a more even pedal stroke, the OP's case, gravity is decelerating you for a smaller amount of time, so you need slightly less power to go up a given grade at a given speed and cadence.
Physics fail. Gravity is accelerating you 100% of the time. It doesn't turn off while you apply power. That's why climbing steeper hills is more difficult. C'mon.
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Old 11-30-08, 12:19 PM
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Let me reword.

You put power into the pedal stroke 20%, you are resisting gravity.

You don't put power into the pedal stroke 80% of the time, you are not resisting gravity so you decelerate.

You spend less time decelerating, you decelerate less because gravity is constant right? You decelerate less, the next pedal stroke comes and you don't have to accelerate as much, right?


The work you do is a function of raising your potential energy as you go up hill, as well as acceleration. If you speed is constant, the only work you're doing is raising your potential energy because your not accelerating.

Given the potential energy rise is a constant, you are now doing less work than if your speed is like a sine wave.
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Old 11-30-08, 12:32 PM
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Originally Posted by Hocam View Post
The work you do is a function of raising your potential energy as you go up hill, as well as acceleration. If you speed is constant, the only work you're doing is raising your potential energy because your not accelerating.

Given the potential energy rise is a constant, you are now doing less work than if your speed is like a sine wave.
I think you need to borrow a grade 12 physics book. Work = Force x Distance. If you neglect losses due to air friction and rolling tire losses. The work is simply a function of the height of the hill and you and your bike's mass. It doesn't matter how you choose to climb the hill fast, slow, accelerating or constant speed the work is the identical.
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Old 11-30-08, 12:35 PM
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What's more work, riding at 20 mph steady or sprinting to 20, coasting to 10 and sprinting to 20?
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Old 11-30-08, 12:42 PM
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riding steady at 20mph...
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Old 11-30-08, 12:46 PM
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This is simple physics, there is no way around it.

His average wattage was 4w less, therefore if the "hill" did not change, he must of had a slightly slower average speed.. it could be outside of the precision of the equipment.
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Old 11-30-08, 12:51 PM
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I can't explain in any clearer terms, riding at a constant speed up a hill takes less energy than mashing up it at the same speed.
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Old 11-30-08, 12:53 PM
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you cant explain it beause it isnt possible.. you can do 1000w bursts every 5 seconds or hold a steady 200w... you will get there at the same time and average 200w either way...
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Old 11-30-08, 01:05 PM
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Originally Posted by Hocam View Post
I can't explain in any clearer terms, riding at a constant speed up a hill takes less energy than mashing up it at the same speed.
Go to analyticcycling.com, plug in the numbers, show us the results, and maybe you'll convince someone. Basically all you're doing is putting up two scenarios and telling us one takes less energy because you say so.
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