Pedal stroke analysis and the Vector

DaveyL

Interesting blog post on the MetriGear site, using their new Vector powermeter:

http://www.metrigear.com/2009/10/20/tun ... ight-data/

I wonder if this will lead to renewed debate on the merits of attempting to modify one's pedal stroke...

Bhima

Interesting. Very interesting...

Actually... I was out today and yesterday smashing it in the peaks and noticed on steep climbs that i'd push harder with one leg when forcing myself to do it seated. I think I made more of an effort to compensate with the other foot and, in doing so, ended up pushing harder with the other one... :roll:

I used to do this a lot, but managed to sort it out by moving one of my cleats... It seems to have come back now out of the blue. :? Once you get into a meditative state and concentrate on pedalling proper circles though, it seems to disappear.

It would be interesting to see how much the troughs between the peaks on those graphs would be decreased by if using eliptical chainrings and if this would make the effect less pronounced...

shockedsoshocked

That guy must look like the cyclist equivalent of a land crab

Percy Vera

Bhima wrote:

Interesting. Very interesting...

Actually... I was out today and yesterday smashing it in the peaks...

What were you smashing in the Peaks? A vector powermeter? Are those things expensive? I hope you picked up all the pieces!

Captain Fagor

That looks like an interesting product - I'll be keeping my eyes on its price / reviews once it's in the marketplace.

GavH

This isn't new, the Polar CS600 Power meter has been measuring L/R pedal forces for ages. Not sure how accurate the Polar is right enough but nevertheless, not a new feature.

Alex_Simmons/RST

GavH wrote:

This isn't new, the Polar CS600 Power meter has been measuring L/R pedal forces for ages. Not sure how accurate the Polar is right enough but nevertheless, not a new feature.

No but the Polar's estimates of L-R are not quite the same as the detailed force analysis that this product claims to provide.

bahzob

The Wattbike also produces a very detailed realtime view of your pedal stroke (and even more detailed post ride analysis) and I'd recommend trying to have a go on one as the results might be interesting,

As an e.g. in my case in "normal" upright riding I found I slightly favoured my right leg, which sort of makes sense as i'm a right footer and my left knee has a knackered cruciate ligament. However moving into TT position the situation was reversed with my left leg taking more of the load. Which may go some way to explaining why my power output is significantly less in TT mode and is something I'll be working on over winter.

Alex_Simmons/RST

The info on the Wattbike site re pedal forces will be updated soon after I pointed out some flaws in what's written there.

bahzob

Alex_Simmons/RST wrote:

The info on the Wattbike site re pedal forces will be updated soon after I pointed out some flaws in what's written there.

I was referring to the feedback obtained while actually using the wattbike, not the info on the website.

Alex_Simmons/RST

bahzob wrote:

Alex_Simmons/RST wrote:

The info on the Wattbike site re pedal forces will be updated soon after I pointed out some flaws in what's written there.

I was referring to the feedback obtained while actually using the wattbike, not the info on the website.

Understand that but it isn't clear:

- how the information was being interpreted (by them or you and if the current web site info is anything to go by, then I'd be scpetical - it would depend on who was doing the interpretation)?

- how one can claim to interpret individual leg measurement when the cranks are connected (IOW - you can't)?

bahzob

Sorry Alex. I can only assume you or your clients have not actually seen/used a Wattbike.

You do actually get real time information on pedal stroke both left/right and within the stroke through the cycle. Its quite easy to validate, just by consciously pressing harder with one leg than the other or by varying where in the rotation you apply power. You can see the graph change shape as a result.

In my case the information is quite consistent and straightforward:

Riding in an upright mode in similar position to when climbing my natural bias is 52% right leg, 48% left. As I said this makes sense given my knackered left knee and and my right leg tends to set the natural rhythm.

I was expecting same in TT position and was surprised to see at end of rides that bias is the other way round, with left leg 52%.

This is interesting because, like most people I think, I put out a lot more power upright than in TT. So I am using Wattbike feedback to experiment with position tweaks and pedal rhythm to see if legs can be balanced out a bit and if so what result in terms of sustainable power in TT position will be.

Note: its early days and I am not saying this will work. Time and 2010 results will tell. All I can say to date is that in my original position it was very hard work even when concentrating to get the right leg to do more than the left. Moving the saddle a few mm sorted this out. It also now feels more comfortable. The thing is that without the info from the Wattbike I would have not realised I even had a problem. In fact if anything I would have thought the right leg was working harder, simply because it was more uncomfortable.

mrc1

bahzob wrote:

Sorry Alex. I can only assume you or your clients have not actually seen/used a Wattbike.

You do actually get real time information on pedal stroke both left/right and within the stroke through the cycle. Its quite easy to validate, just by consciously pressing harder with one leg than the other or by varying where in the rotation you apply power. You can see the graph change shape as a result.

In my case the information is quite consistent and straightforward:

Riding in an upright mode in similar position to when climbing my natural bias is 52% right leg, 48% left. As I said this makes sense given my knackered left knee and and my right leg tends to set the natural rhythm.

I was expecting same in TT position and was surprised to see at end of rides that bias is the other way round, with left leg 52%.

This is interesting because, like most people I think, I put out a lot more power upright than in TT. So I am using Wattbike feedback to experiment with position tweaks and pedal rhythm to see if legs can be balanced out a bit and if so what result in terms of sustainable power in TT position will be.

Note: its early days and I am not saying this will work. Time and 2010 results will tell. All I can say to date is that in my original position it was very hard work even when concentrating to get the right leg to do more than the left. Moving the saddle a few mm sorted this out. It also now feels more comfortable. The thing is that without the info from the Wattbike I would have not realised I even had a problem. In fact if anything I would have thought the right leg was working harder, simply because it was more uncomfortable.

I think alex is meaning that you can't use the watt bike to show which individual leg is doing what, because as you push down with the left you pull up with the right?

Either way I still think it is a really useful tool and something I would definitely like to have a go on as balancing out the strokes has got to be beneficial (whether it is a combination of left and right or the individual leg - an imbalance is an imbalance).

amaferanga

bahzob wrote:

Sorry Alex. I can only assume you or your clients have not actually seen/used a Wattbike.

You do actually get real time information on pedal stroke both left/right and within the stroke through the cycle. Its quite easy to validate, just by consciously pressing harder with one leg than the other or by varying where in the rotation you apply power. You can see the graph change shape as a result....

I think the point is that your other leg is also connected to the cranks so the L/R measurements are not fully independent.

bahzob

All I can say is that the Wattbike is very consistent in the information it provides.

When you pedal if you make a bit more effort with one leg or another then this is reflected in real time. And you can see how the push/pull rations change according to subtleties of technique.

If you havent tried one then I'd suggest doing so. It may prove interesting.

Alex_Simmons/RST

amaferanga wrote:

bahzob wrote:

Sorry Alex. I can only assume you or your clients have not actually seen/used a Wattbike.

You do actually get real time information on pedal stroke both left/right and within the stroke through the cycle. Its quite easy to validate, just by consciously pressing harder with one leg than the other or by varying where in the rotation you apply power. You can see the graph change shape as a result....

I think the point is that your other leg is also connected to the cranks so the L/R measurements are not fully independent.

Correct - since the cranks are connected, you cannot distinguish exactly what each leg is doing.

It is not an independent measurement of each leg.

e.g. is one side "less forceful" than the other because it is pushing harder or because the other leg is unweighting less? You cannot actually know from a system that only measures the nett forces.

And even if it did measure such forces and you see an "imbalance"- this still doesn't actually suggest that something is "wrong" and needs correction.

Alex_Simmons/RST

bahzob wrote:

The thing is that without the info from the Wattbike I would have not realised I even had a problem. In fact if anything I would have thought the right leg was working harder, simply because it was more uncomfortable.

What concerns me here is that it may not actually be a problem - you may be misinterpreting it to be a problem that in reality isn't actually a problem.

This is my main point - just because we can measure something, doesn't mean it is all that important. And we have to be very clear about what the measurement actually represents (not what it is portrayed to represent).

Sure it's interesting and can be fun and by all means go for it but think very critically about what the information is actually telling you about performance and whether in fact taking action is warranted.

I would be far less concerned with addressing any L-R differences which may not be an actual problem (hey I should know) than in the sum total power I can produce (which is what matters).

bahzob

Alex: you seem just to be arguing from theory. A bit like the one that says bees cant fly.

Have you actually seen or used a Wattbike?

Also very puzzled by your other comments:
- I and many others generate less power when in TT position. In fact a lot (most of?) TT is finding the right compromise between power and position. This loss of power is definitely a problem and worth investigating with a view to reducing as much as possible. Most riders use trial and error for this of course.

- WIth this in mind your view on power seems a bit simplistic. Of course I am concerned with total power I can generate. But I am also aware that its effective sum total power I need and this is not just a question of physiology and maximising FTP but also mechanical efficiency.

- And as someone who endorses a scientific approach to training bit surprised by your attitude. Science often proceeds by way of observations leading to theory and subsequent tests:
I have 2 observations:
- My sustainable power is significantly less in TT position than upright
- There is a suprising and consistent difference in the readings of leg balance between the 2 positions. (Note from a measurement pov the interesting thing is the consistency between the sets of data. If the Wattbike was measuring nothing useful there would be no consistency, just lots of noisy data.)

This alone should be enough for scientific curiousity to be picqued.

Thats all I'm saying now. Next is to do some focused training with a view to reversing the leg bias. This may or may not yield results. If it does then we can discuss what it actually means.

Alex_Simmons/RST

bahzob wrote:

Alex: you seem just to be arguing from theory. A bit like the one that says bees cant fly.

And experience and knowledge gained from investigating these issues over some time.

bahzob wrote:

Have you actually seen or used a Wattbike?

Yes. The Cycling Australia Paracycling development guys here have one and were doing some testing on it with some of my paracycling riding colleagues over the last couple of months. I personally did not ride it. I have my own such trainer.

bahzob wrote:

Also very puzzled by your other comments:

Which ones?

bahzob wrote:

- I and many others generate less power when in TT position. In fact a lot (most of?) TT is finding the right compromise between power and position. This loss of power is definitely a problem and worth investigating with a view to reducing as much as possible. Most riders use trial and error for this of course.

I haven't suggested otherwise. Besides, what has that got to do with the L-R measurements or the torque curves of the Wattbike?

bahzob wrote:

- WIth this in mind your view on power seems a bit simplistic. Of course I am concerned with total power I can generate. But I am also aware that its effective sum total power I need and this is not just a question of physiology and maximising FTP but also mechanical efficiency.

Then it is you that has the simplistic view - if you think you can impact on your "efficiency" in such a way that it will enable you to produce more power. Your efficiency is inherit physiological characteristic. No amount of fiddling with pedal stroke is going to change that.

bahzob wrote:

- And as someone who endorses a scientific approach to training bit surprised by your attitude. Science often proceeds by way of observations leading to theory and subsequent tests:

Yes but what you are observing is not new and has been well and truly studied for decades. Pedal force measurement systems have been utilsied in cycling performance research for a long time. Wattbike is not bringing anything particularly novel to the table.

bahzob wrote:

I have 2 observations:
- My sustainable power is significantly less in TT position than upright

That's great that you know the difference in power between an upright road bike position and a TT position (or different TT positions). But that's only part of the story.

The Wattbike can't however help you determine which position (of several say TT positions that you might experiment with) is actually faster - since it cannot tell you anything about your aerodynamics. And speed is what matters with respect to TT.

The best measure for that is you power to CdA ratio.

bahzob wrote:

- There is a suprising and consistent difference in the readings of leg balance between the 2 positions. (Note from a measurement pov the interesting thing is the consistency between the sets of data. If the Wattbike was measuring nothing useful there would be no consistency, just lots of noisy data.)

This alone should be enough for scientific curiousity to be picqued.

I have no doubt that the Wattbike is very accurate and consistent in what it is measuring. I am not disputing that. My ruler gives me the same length everytime I measure my TV screen. Doesn't mean it's important though.

My point is - given you have a measured difference (and we don't quite know the reason for that measured difference since the Wattbike can't distinguish the effect of legs connected by a crank system) - on what basis do you think you should do something about it? And what are you proposing to do?

Here's an example, I know people who, when having pedal forces measured, find that the "imbalance" moves from one side to the other depending on their power and cadence. Should they "do something" about it? If so, what?

bahzob wrote:

Thats all I'm saying now. Next is to do some focused training with a view to reversing the leg bias. This may or may not yield results. If it does then we can discuss what it actually means.

Good luck with it.

It is fun for sure.


I'm not trying to be a pain in the butt (sounds like I failed ) I'm just wanting people to think critically about information they are presented so that they make well informed decisions/actions.

I tell you what would be interesting - Wattbike force/torque data from using an inertial pedal weighted system (you pedal one-legged with a ~10kg weight attached to the opposite pedal to simulate the inertial load of a "passive" leg). It is very close to the sort of data you get with independent pedal forces measurement systems when cycling normally.

I'm hoping to try out something similar myself before too long since I have a very clear power imbalance left to right.

DaveyL

What got me thinking when I read the blog post I linked to at the start of this thread was such a discrepancy between L and R as recorded by the Vector. Again, these are not decoupled, obviously, but it does make me wonder what is going on to cause the difference.

And, possibly naively, I figured that if you were somehow able to "smooth out" the data from L and R by levelling the two peak forces, your overall normalised power would be lowered and you would be "more efficient" in the same way that someone who paces a flat TT with a VI of 1 is generally "more efficient" than someone whose VI is 1.2, for example (I know this pacing argument doesn't always hold).

Perhaps this is the type of "efficiency" Bahzob is searching for, as opposed to what I presume Alex is talking about - muscular efficiency.

eh

Be careful reading much into the link in the OP, since they are showing a Force measurement, not Power. I suspect although haven't followed the analysis through properly that Peak Power, will be when the rate of change of force is at it greatest i.e. the steapest part of the slope.

oldwelshman

Just ride the track and technique will improve

bahzob

Thanks for the advice Alex. Like I said I dont know if there is any link between the L/R difference and the power output of my normal and TT positions. Its just that I got an unexpected result when I tried out the Wattbike that got me curious.

However I think we fundamentally disagree on one thing. You seem to think efficiency is something that's inherited and you cant change. I disagree and believe it can, both in terms of bike set up and pedal skill.

Honestly I dont understand your view. Even assuming you are just born that way you surely you dont believe that you have the same efficiency regardless of seat height, cleat adjustment etc?

And sorry you are being simplistic when you say the best measure is power to CdA ratio. Power is not constant, it changes with position to achieve a given CdA. And for the same CdA its the case that power will be different as a result since one position may be less efficient or more strained than another. Already being aware of this I'll be doing some wind tunnel testing over the next couple of months to hopefully understand it a bit better.

Edit: http://www.roadcycling.com/training/pedalingtechnique.shtml just to check you are saying this is rubbish right?

bahzob

oldwelshman wrote:

Just ride the track and technique will improve

Tracks too dangerous for an old man like me ....

However I do have a fixed bike that I started to use for winter training last year. Regardless of what it may (or may not do) for technique its just b good fun so its bike of choice over the grey months now.