Bike Fitting and Power Meters

[RapDaddyo]

I have recently gone through a bike fitting process with a cycling friend and the process has refined my thinking about bike fitting and power meters which I thought I'd share. A good friend recently got an awesome bike (BMC SLC01 w/Campy Record, Zipp 404s and PT SL). He was fitted by the most highly regarded fitter in LV and the size looks right. But, he has been struggling with finding a saddle that didn't cause numbness and that was comfortable. After a couple of trips to the LBS, he asked me for help. Notably, none of the fittings were done dynamically at power. So, I decided to test a theory I have been working on about fittings. I put him on my trainer and had him first ride at a moderate power (~200W) for about 5 mins. I then had him ride at ~350W (his FT is ~300W) for a few minutes and his position on the saddle changed markedly. He slid forward at least an inch if not more, placing him on a very different part of the saddle with respect to saddle width at the sitz bones. After lots of experimentation, the end result was a different saddle (Specialized) and a different saddle position (further forward). He is now happy with both his saddle and his position. My conclusion is that one has to ride at power levels that force the body to find its optimal position to apply leverage to the cranks. Yet, I don't think this is how most people get fitted. My observation is that most fittings are done either statically or dynamically but at low power. I now think these approaches are flawed. I am also becoming a believer in the Specialized approach to different saddle widths to accommodate different sitz bone widths, but I wonder if two widths is sufficient.

 

[shawndoggy]

A good friend recently got an awesome bike (BMC SLC01 w/Campy Record, Zipp 404s and PT SL).

Or the other way to look at it is how do you know your friend isn't accustomed to making power in a less than optimal position, and that when changed to a less than optimal position on the new bike he felt better? How was his old bike set up in relation to KOPS under power?

Part of making power from bike to bike or position to position is that the body needs to become accustomed to the position. Lots of people report that their power is down during their first few rides on the TT bike, but that once they become accustomed to the position the power comes up.

 

[frenchyge]

Part of making power from bike to bike or position to position is that the body needs to become accustomed to the position. Lots of people report that their power is down during their first few rides on the TT bike, but that once they become accustomed to the position the power comes up.

So are you saying that people should do several low-power rides once they are fitted, to try to adjust to the new position before being forced back into their old habits by high-power excursions?

 

[otb4evr]

My conclusion is that one has to ride at power levels that force the body to find its optimal position to apply leverage to the cranks. Yet, I don't think this is how most people get fitted. My observation is that most fittings are done either statically or dynamically but at low power. I now think these approaches are flawed.

RDO,

I *completely* agree with you. I have done several fittings like this and am very pleased with the results.

BTW It also works with TT bikes...

Jim

 

[RapDaddyo]

Or the other way to look at it is how do you know your friend isn't accustomed to making power in a less than optimal position, and that when changed to a less than optimal position on the new bike he felt better? How was his old bike set up in relation to KOPS under power?

Part of making power from bike to bike or position to position is that the body needs to become accustomed to the position. Lots of people report that their power is down during their first few rides on the TT bike, but that once they become accustomed to the position the power comes up.

I'm talking primarily about the fore/aft position on the bike (assuming the bike is fundamentally the right size and that the saddle height is fundamentally correct, i.e., not egregiously wrong). What I'm saying is that the body will position itself correctly on the saddle to apply leverage on the cranks, but only if you force it to by riding at a reasonably high power. At lower power levels (or worse yet just sitting on the bike), I don't think your body will position itself correctly. A slight fore/aft change in position is huge because it positions one's sitz bones on a completely different part of the saddle width-wise. My friend's saddle was positioned too far back on the bike, in spite of 3 trips to a very highly regarded bike fitter. And I think this only surfaced when he rode at the higher power levels, which forced him to slide forward to get adequate leverage on the cranks.

 

[RapDaddyo]

RDO,

I *completely* agree with you. I have done several fittings like this and am very pleased with the results.

BTW It also works with TT bikes...

Jim

Hi Jim,

That's interesting that you have discovered this independently. I don't consider myself a bike fitting expert and have always gone to an expert (e.g., Kyle in Philadelphia fit me on my current bike), but I have read every single discussion of bike fitting here http://www.cyclemetrics.com/Pages/FitLinks/bike_fit_links.htm. Not one of these links talks about dynamic vs. static fitting and I have never ever seen a suggestion such as I make in my OP and which you apparently discovered yourself. So, it's far from common practice.

 

[acoggan]

What I'm saying is that the body will position itself correctly on the saddle to apply leverage on the cranks, but only if you force it to by riding at a reasonably high power.

I completely agree. However - and I think this is a key point - there is no need for a powermeter to accomplish this, and in fact using a powermeter may work against you. The reason I say that is because of the effects of accomodation mentioned by shawndoggy, i.e., just because something is worse (or better) at first doesn't mean that it won't be better (or worse) after a period of adjustment. Acute power measurements don't address this issue, yet many fall into the logical trap of assuming that they can use a powermeter (and/or heart rate monitor) to easily achieve the "perfect" position.

 

[WarrenG]

Power, aerodynamics, position, speed. Which one matters most?

 

[RapDaddyo]

However - and I think this is a key point - there is no need for a powermeter to accomplish this

I agree that a PM is not the key part of this. It only serves to allow someone to ride at realistic sustained yet high power levels. I don't know where he would have positioned himself at, say, 400W, but it doesn't matter much because that's not the intensity that matters.

in fact using a powermeter may work against you. The reason I say that is because of the effects of accomodation mentioned by shawndoggy, i.e., just because something is worse (or better) at first doesn't mean that it won't be better (or worse) after a period of adjustment. Acute power measurements don't address this issue, yet many fall into the logical trap of assuming that they can use a powermeter (and/or heart rate monitor) to easily achieve the "perfect" position.

I agree that one shouldn't assume that a position is "wrong" because they initially make less power in that position than in another position. And, we didn't use the PM for that purpose. Rather, we used the PM simply to get him in the desired range where it matters -- the upper end of his sustainable power range. Maybe FT would have been even better, but I wanted him to have to push it a bit more (not a lot more) than normal.

 

[shawndoggy]

So are you saying that people should do several low-power rides once they are fitted, to try to adjust to the new position before being forced back into their old habits by high-power excursions?

Pretty much. In my experience (translation: the last time I goofed up my own position) when changes in position are made they need to be made during the off season. This time of year (for those of us in the northern hemishpere anyway), when I'm in race/high intensity interval/A race/peak mode, I won't change anything. No saddle up or down or forward or back or seat change, or new shoes or anything like that.

Maybe it's just me, but when I've gotten my body to squeeze out those last few watts, it's very particular about doing it in the same position. The last time I tried a drastic position change in the middle of race season (and by drastic, we're talking about seat hight and fore aft adjustment of less than a centimeter either way), I ended up with a knee pain that sidelined me for a couple of weeks. Same for changing my shoes mid season a couple of seasons ago... the cleat position was just different enough to compromise my power for a while. I'm now resigned to making position and equipment changes in the fall when I'm just riding for fun, before I'm back on the L4 interval grind.

Essentially, by making the changes at the beginning of my training cycle, I re-learn how to make high end power from the ground up in the new position. Again, this is my own experience and application to your situation may vary.

 

[acoggan]

Power, aerodynamics, position, speed. Which one matters most?

Speed, obviously. However, unless you're testing and racing on an indoor velodrome, speed is too variable to be of any real use.

 

[SolarEnergy]

I have recently gone through a bike fitting process with a cycling friend and the process has refined my thinking about bike fitting and power meters which I thought I'd share. A good friend recently got an awesome bike (BMC SLC01 w/Campy Record, Zipp 404s and PT SL). He was fitted by the most highly regarded fitter in LV and the size looks right. But, he has been struggling with finding a saddle that didn't cause numbness and that was comfortable. After a couple of trips to the LBS, he asked me for help. Notably, none of the fittings were done dynamically at power. So, I decided to test a theory I have been working on about fittings. I put him on my trainer and had him first ride at a moderate power (~200W) for about 5 mins. I then had him ride at ~350W (his FT is ~300W) for a few minutes and his position on the saddle changed markedly. He slid forward at least an inch if not more, placing him on a very different part of the saddle with respect to saddle width at the sitz bones. After lots of experimentation, the end result was a different saddle (Specialized) and a different saddle position (further forward). He is now happy with both his saddle and his position. My conclusion is that one has to ride at power levels that force the body to find its optimal position to apply leverage to the cranks. Yet, I don't think this is how most people get fitted. My observation is that most fittings are done either statically or dynamically but at low power. I now think these approaches are flawed. I am also becoming a believer in the Specialized approach to different saddle widths to accommodate different sitz bone widths, but I wonder if two widths is sufficient.

Funny because I made exactly the same changes to my fit. New seat post (a straight one) and a specialized seat (paid $120).

A friend of mine owns a fitting company. That's all they do. They don't sell nothing.

They use a pm, and video film you. They then transfert the video data in a computer software for biomechanical analysis. They evaluate your flexibility strength and weakness. They then base their fitting recommandation on all those factors. They encorage you to buy more than one session.

In fact, I find that fitting is a continuous work in progress.

 

[Lonnie Utah]

A friend of mine owns a fitting company. That's all they do. They don't sell nothing.

Got a link?

 

[beerco]

After lots of experimentation, the end result was a different saddle (Specialized) and a different saddle position (further forward).

Something to think about - when I see people riding on the nose of their saddle and complain of numbness, instead of moving the saddle forward I have them drop it by a few mm. Essentially, it's the same effect as moving it forward but it doesn't affect reach but does close the hip angle some.

If they're sliding back on it, it's time to raise the saddle.

 

[WarrenG]

Speed, obviously. However, unless you're testing and racing on an indoor velodrome, speed is too variable to be of any real use.

Selecting a position based on power OR aerodynamics is secondary to choosing the position that allows the rider to go fastest (speed).

 

[meandmybike]

I am also becoming a believer in the Specialized approach to different saddle widths to accommodate different sitz bone widths, but I wonder if two widths is sufficient.

I've thought the same thing. People are prepared to pay a premium for a made to measure frame, hundreds of dollars/pounds for a bike fit, even custom shoes, so why is no one offering made to measure saddles?

 

[frenchyge]

I've thought the same thing. People are prepared to pay a premium for a made to measure frame, hundreds of dollars/pounds for a bike fit, even custom shoes, so why is no one offering made to measure saddles?

Heh. I was thinking what a crummy job that would be (taking saddle measurements for custom saddles), but then I remembered a little device they have at my LBS. It's a heat-sensitive rubberized black pad which you stand on for a few minutes, and when you step off there's a heat-generated colored image in the shape of your feet where they contacted the mat. It's designed to show the amount of arch someone has in their feet for help in selecting the right shoe, but maybe people could sit on a similar device in order to see the shape of the contact patch between their body and a bike seat. A seat core could then be customized based on that, or the closest one of several could be selected. Cool idea?

 

[peterpen]

Heh. I was thinking what a crummy job that would be (taking saddle measurements for custom saddles), but then I remembered a little device they have at my LBS. It's a heat-sensitive rubberized black pad which you stand on for a few minutes, and when you step off there's a heat-generated colored image in the shape of your feet where they contacted the mat. It's designed to show the amount of arch someone has in their feet for help in selecting the right shoe, but maybe people could sit on a similar device in order to see the shape of the contact patch between their body and a bike seat. A seat core could then be customized based on that, or the closest one of several could be selected. Cool idea?

Specialized has basically the same thing - a pad of 'memory foam' that customers sit on and records the width of sit bones.

 

[RapDaddyo]

Specialized has basically the same thing - a pad of 'memory foam' that customers sit on and records the width of sit bones.

That's what I hear. I haven't tried it, but my friend used it to select his saddle. The problem is that there are only two widths available and I would think one could figure out which is the better fit by simply sitting on each one in the riding position. It's sort of like going to the shoe store where the shoe salesman precisely takes your foot measurement and then says, "Okay, you're an 11C. Now, which shoe size do you want, Small or Large?"

 

[SolarEnergy]

Got a link?

No unfortunately. I just called him to ask for his link, he just informed me that he left the business. He still offers a fitting service on a personnal basis though, but he has less equipement.

He told me that with the experience he accumulated, he finds that fitting with a powermeter can be missleading, pretty much for the same reason Andy mentionned above, so he doesn't use one at the moment. Somehow though, I disagree. Even if power increase shouldn't be the only aim while fitting, I still think it's good to know the imediate impact of any change on power (if there is any).

His methodology now involve video equipment, all limbs are measured, flexibility evaluated. Current position is evaluated and noted. Target position is explained. He says that often, the targeted position isn't set in one meeting. He rather plan a bunch of modifications by few milimiters every time. Subject don't necessarly have to come back every time (they probably leave the appointment with a 'fitting plan' I guess).

An appointment is 2hr long. If you live near montreal, just pm me, I'll give you his phone number.

Cheers