Bike Fit 101: Proper Knee Extension on a bike

I was asked a  really good question this week.....one I look past a bit and take for granted since I do so many bike fittings.  It has to do with the amount of knee extension one should have at the bottom of their pedal stroke.

When I pointed out to this client that his knee extension on the right compared to the left side was nice and even at 37 degrees from full extension on both sides he asked, "I thought that should be between 25 and 35degrees?"

He's not wrong, especially if you look at much of what has been written about bike fitting in the last 20 years.  Most of the texts label the acceptable range at 25-35 degrees.

So where did I go wrong, when I assumed that 37 degrees was "good"?  Actually, I didn't.

The discrepancy lies in the fact that most of the books on bike fitting were written using static measuring methods -- that is stopping the cyclist mid pedal stroke and lining up a goniometer (joint angle measuring device) at their knee.  Actually, most bike fits are still done this way and that's a shame.  

When you use dynamic measuring methods, as I do with the infrared motion capture system in my Studio, you get much better data about the rider's actual pedaling posture.

What the static measuring fails to take into account is ankle and hip motion.  Because the rider has to stop their pedal stroke, it's rarely possible to replicate the correct ankle placement when measuring at the knee.  Some fitters have tried to use video to see what position the ankle sits at at the bottom of the stroke.  But really this is little more than a guess -- you're eyeballing whether it looks close to what appears on the video, and whether the client can actually hold it there is another thing altogether.  An incorrectly mocked up angle at the ankle can have a drastic effect on the knee measurement as well.

Why not measure right off the video with Dartfish software or some other program?  The short-coming here is that you end up setting a pixel on a screen at the joints, and even on a very large screen the displayed size of the rider is very small, and getting that joint marker off by even a small amount contaminates the data.  Generally the margin of error with video runs about +/-10% while with infrared motion capture it runs about +/-0.5%.

So what angle does the knee work at across most populations?  Well, roughly between 30-40 degrees...but there are numerous situations where a rider is best fitted by allowing them outside those vague lines.  That is another post entirely.

Next post we'll look at how pelvic posture and mobility affects saddle placement -- maybe even dip into how some sacro-iliac (SI) joint dysfunctions play into the fitting.

Dura Ace Di2 with SRAM XX mountain crankset

Di2 and a custom Seven -- doesn't get much better

Alternate gearing is really popular especially here out west where we have lots of hills to contend with.  The triple crank used to be standard fare, but the advent of the compact crankset, and the improvements it brought (smoother shifting, better chainline, less weight) started the extinction of the triple.

The one downside of a compact, however, is that you can't get gearing quite as low as a triple so some triple-to-compact converts were left wanting more.

The use of mountain bike cassettes with road drivetrains solved this issue, though and the idea isn't new -- when everything was nine speed it was pretty easy to do with the right choice in components.  The switch to 10-speed temporarily inhibited these setups, but work-arounds were found and soon enough SRAM developed their 10-speed mountain group and made it fully compatible with their road group -- a great idea in my mind.  So I had a number of clients do SRAM Red drivetrains (compact cranks, shifters, etc) and use a SRAM XX 11-36 cassette with a SRAM XX derailleur.  Now with their WiFli setup being ubiquitous, this is even easier to do now with many more component choices.

One drawback to using a mountain cassette and a road compact crank, at least from the standpoint of a road rider, is the large steps between gear shifts on an 11-36 or 11-32 cassette; compared to an 11-23/25/28.  A few years ago, I built a custom Seven (Ti/carbon) for a client who wanted the low gearing without the big steps between gears, and we settled on a hybrid solution -- we went with a SRAM Red 11-28 cassette but instead of the SRAM Red compact crankset, we settled on a SRAM XX mountain cranks with the 28-42 chainring combination.  We still included a mountain component but we did it from the opposite side that you'll normally see.

Climbing shifter added

regular Di2 der with 12-27 cassette

This provided him with the low gearing he wanted (and he had little use for the high end gears of a road crankset anyway) and the small steps between gears.  It worked flawlessly and for 3 years he's been putting many thousands of miles on this setup without any difficulty.

Recently he came in to see me with questions about the functionality of Dura Ace's Di2 electronic setup.  I told him the reviews were fairly glowing -- not only does it sport a high "cool" factor, it works exceptionally well.

The question would be could we get his desired gearing on it?

I did some research and found that a few people had gotten it to function with a 32-tooth cassette in back, but this presented the "big gear step" problem as before.  Then I remembered that K-Edge had modified a setup for mountain bikes, calling it Ki2 -- they adapted the rear derailleur by custom designing a new, longer pulley arm.  After looking at it in depth and a phone call or two it was clear they hadn't modified the front derailleur at all, and it was shifting an XTR 2X crankset (which I believe was 26-39).  I already knew they Di2 front derailleur could shift a 16-tooth difference between chainrings (which is standard compact design 34-50) but with my client's 28-42 SRAM XX crankset, we were only dealing with a 14-tooth drop.

Dura Ace 7970 front chainrings are thicker and stiffer than most -- would the SRAM XXs be stiff enough?

SRAM XX was designed to shift ultra-crisp so the rings are 2mm thicker than most and the special bolt attachment (the BCD) is set wider than regular mountain cranks to further stiffen the drivetrain.

I was pretty confident that it would shift perfectly.  But you never can tell with mismatched components, and if we went ahead on this, I was on  the hook for a few thousand dollars worth of components if it didn't work -- not to mention all the work of repeated tearing down and rebuilding with his SRAM Red components if this experiment failed.

Well, long story sorta shorter, is that it works great.  The Di2 front derailleur shifts perfectly over the SRAM XX crankset.  No modifications or calisthenics necessary to get it working.  Check it out:

Even though the bike is all done and waiting for it's owner to return for it, I can't help but go over to it and take the shifting through it paces just to see it work.  About every 10 minutes I've been compulsively returning to it, just because its fun to see a custom project come together so well.  Nerd, I know.

Brush Strokes -- Designing and Fitting a Custom Bike

Building a bike, custom or not, is a lot like painting a picture.  You start with very broad, coarse strokes that don't really resemble the end product very much at all except in the broadest sense, and slowly those brush strokes get smaller, more careful and exact and, if you have a skilled painter, eventually you get a beautiful piece of art work.  Anyone can go through the steps, but not everyone has the skills gained from years of training and practice to do them well.

When it comes to painting, I suck.

I can go through the steps -- I can make broad brush strokes to begin with, and refine those to render a painting, but it looks terrible, because it's not something I've trained for or practiced.

In much the same way, anyone can go through the steps of bike fitting or custom bike design, but if they don't have the skills and/or the practice the outcome can be equally ugly.

Building a custom bike is even more tricky because, when done right it is a painting completed by two or more people.  The custom bike fabricators (machinists, welders, finishers, painters, etc) often don't see the rider first-hand.  The rider often just visits their local bike shop who is then supposed to communicate the fitting information to the fabricator.  The problem, and one I've seen a number of times, is that the local shop doesn't really know how to best fit their client, and the task of designing their bike is lost on them, so they leave much of the heavy lifting to the fabricator -- who has never seen the client.  This is when you get a custom bike that at best doesn't take full advantage of the possibilities of the custom build, and at worst (and more common than you think) actually doesn't fit any better than a stock bike off the shelf. 

I recently had a custom bike in the Studio, built elsewhere, in for a fitting and the very expensive titanium frame had the exact same dimensions as the clients previous Cannondale, because those were the dimensions that the shop sent to the custom fabricator.  Now there may be a situation where this would be the best geometry for a client, but that wasn't the case for this client.....that's why they were in to see me for a fitting.

The fitter needs to have the first and last word on the geometry of the bike as it pertains to the fit of the contact points for the rider.  This only makes sense since they are the ones actually seeing the client in the flesh.

In this same vein though, I will defer to the judgment of the fabricator when it comes to angle choices and axle (think about where the wheels end up) placement of the bike.  Good builders have an intimate understanding of the bike they're building -- how the material, tube selection, mitering, butting, welding etc will affect the ride -- and I think they're in the best position to decide if we need to, for instance, slacken a seat angle a quarter of a degree, lengthen/shorten a chainstay a few millimeters, or increase the rake of a fork to achieve a particular trail measurement.  I'm very happy to work with Seven Cycles on the majority of my custom bikes because they excel at this and still will listen to and defer to my opinion on some of these decisions if I can make a compelling case on behalf of my client.

So, on to the process:


1.  The first step is the most 'coarse', where we're determining contact points -- trying to find the most neutral fit position for the saddle and handlebars so that the location of each exists in the middle of an imaginary box.  The box represents the likely and possible alternate positions -- some higher, some lower, some further back, some further forward.  If we can design the frame and then the rest of the bike around these points, so that any point within the box is possible, then we'll have a very easy-to-fit bicycle.

2.  I can take these initial contact points and work backwards to find some of the basic frame dimensions -- I usually start with either effective top tube length and head tube length, or frame stack and reach.  I have some custom excel files I built years ago where I can plug in any combination of head angle, head tube length, stem length and rise, wheel diameter, headset type, headset spacers, seatpost heights, seatpost setbacks, seat angles, etc etc etc and it will give me the dimensions I need.

3.  This bare-bones information is sent to the builder for the first drawing and specs.  From these rudimentary measurements they can flesh out the finer details of the frameset -- the head and seat angles, amount of top tube slope, lengths of all tubes, and not to be forgotten, fork axle to crown, rake.  Another huge benefit of working with Seven is that they build their own custom raked fork in 3 millimeter increments.  Being able to control the position of the front axle is critical to translate the rider's custom positioning into the best possible weight distribution across the length of the bike.  Standard stock forks come in usually just 2 or 3 different rakes, which can severely hamper the handling of a bike.  Ask any of your very tall or very short friends who ride and you'll hear numerous stories about speed wobbles and poorly handling (especially downhill) because the forks for most stock bikes are designed for the middle sizes (53 - 57 cm), not the big and the small.

4.  Once we get the specs back from the builder I can review them with the client and explain what I'd like to change (if anything) and why.  Or I explain why I like the specs, and to the best that I can, I try to "show" the client how these specs will best suit their fit, riding style, and goals for this bike.  I may go back and forth with the builder a couple times until we end up with the specs we're looking for.

As I mentioned before, vetting the specs is critical, and should be the job of the fitter, not the builder since the fitter (me) is going to be the one working one-on-one with the client and the one ultimately responsible for their satisfaction.

5.  Next,  we sign off on specs and the builder begins fabricating the bike

6.  Get the frame, start building.  This is where choosing the correct components is key -- the right crank length, appropriate setback on the seatpost, making sure the length of the stem and the reach of the bars don't cause any problems with the overall reach of the bike that we're looking for. 

This is where I build the bike so that the bars and the saddle get set in the center of that imaginary box -- by properly designing the frame I should be able to get the position here with all the parts being set up "in the middle".  What I mean by this is the saddle is clamped in the middle of the rails by the seatpost, the stem is not overly long or short (maybe 105-110 mm) nor does it have a drastic rise or decline to it (+/- 10 degrees), there aren't a ridiculous amount of spacers under the stem (most carbon forks are limited to a maximum of 35-40 mm of spacers), etc.

If I can do this, then when we go on to the next step, the first fitting, we'll have lots of adjustability in all the settings.

7.  First fitting.  We'll be 90-95% done or more after this fitting.  This goes very smooth since we've done a lot of the heavy lifting before hand and eliminated lots of potential problems because of the way we designed the bike.  The adjustments we have to make are often very small -- a millimeter or two here and there -- precisely because we did plan meticulously ahead of time.

Of course, I still use the capabilities of the infrared system by Retul (every bike I build, custom or not, includes a full bike fit).

8.  Then the client needs to ride about a dozen times.  Often we need time on the bike to fully assess how certain changes will affect the rider.  Muscles and other soft tissues need time to adapt to the new lengths that they're working at. 

9.  Second fitting -- we'll be 98-99% after this fitting.  Because we need time riding to see how the body will adapt, I include follow ups for the first year in the cost of a new bike (and all my fittings for that matter) -- I don't want there to be a barrier, like having to fork out another $50 or more, for my clients checking in to make sure their fit is progressing as we expected.


When clients can't come in for a follow up -- I build quite a few custom bikes for people who drive or fly in from all over -- we're often far enough along into the process that the changes we'll make are known entities (meaning we're often very sure which direction, if any, we're going to have to change things), usually very small, and don't require equipment replacements, only modifications.


A raised seat by a few millimeters; a small tilt of a handlebar; a mild tweak of a cleat.  In the case of clients from out of state, we can often consult remotely (Skype for instance) and work through the change without any trouble.




So there's a lot that goes on in this process.  Sometimes the whole thing can take just a few weeks, other times it can take a few months.  And whether we're building a stock bike or a custom one, the end game is the same -- making sure we get the best fitting, best riding bike for the client.  And the only way we can do that is painstakingly making our brush strokes, one step at a time, until we end up with our masterpiece.


--J

Rules of Bike Fitting

This is by no means a comprehensive list, and I'm sure that it'll keep growing and morphing but here you go:

1.  You must use Reason  --  Reason is King.  If you don't have a solid basis for why you're doing something, then you shouldn't be doing it.  I do a lot of fittings for people that have already had a bike fit and are still having difficulties on the bike.  So many of these failed fittings are the result of the fitter making changes to their fit without any real reasoning behind them.  Often they fit a certain way because "that's how we've always done it."  That's not good enough.


2.  Always consider the "whole" while looking at the parts -- Regional Interdependence is the idea that parts of the body (even distant ones) are inextricably linked, and affect one another.  This is a very common theme drilled into every PT student, and one that is especially important when on the bike.  The bike is one of the few tasks where we move with and against a device that we attach to at 5 different points (you can make the argument for 6 contact points if you consider each sit bone, and therefore each side of the pelvis to be separate entities) and when we make a change at one of these points it has the ability to create changes everywhere else.  This is why good bike fitting is so difficult -- a change in foot position is very likely to cause changes even at the rider's shoulder and neck -- reading and trying to predict these outcomes comes only from a deep knowledge base.


3.  A bike fitter needs lots of academic training AND lots of practice -- To successfully combine #1 (Reason) and #2 (Regional Interdependence) requires a lot of education and training, and it's important to realize that these are two different things.  Education is learning all the basics about the bike and the human body (and the human body information is significantly greater in scope) while training is the act of applying this knowledge.

The best scenario would be to have  a lot of both.  There's no accounting for the huge benefit of having thousands of hours of "deep practice" applying what's been learned at multiple years at University.  I remember when I was getting ready to graduate from PT school, my clinical instructor told me that while I knew a lot then (I have forgotten more information than I remember; you get so crammed full of data in PT school) it would take about 4 years of being out there and working to really "figure it out".  I wasn't sure exactly what that meant at the time, but sure enough after about 4 years I started to feel like I could fully trust my instincts when it came to mechanical assessment.  After that, reading someone's movement pattern was something I could do quickly by watching them repeat it (walking, lifting, throwing, whatever) only couple times instead of pouring over video for 10 or 15 minutes.

Interestingly, I discovered, years later, that the four years of practice actually lined up with what researchers have found when studying what it takes to become "expert" at something.  Whatever the task, (shooting a basketball, programming a computer, playing the piano) spending 10,000 hours in dedicated practice of this task can make you as close to an expert as you're likely ever going to be.  Working 4 years at roughly 2500 hours per year -- the math is about right.

4.  Bike Fitting at its core is about Balance --  This can refer to weight distribution on the bike fore-aft -- having the right amount of weight on your hands, feet, and butt -- as well as lateral balance -- most clients are surprised to find out that they don't sit in the center of their bike.

I would argue that this balance can refer to the symmetry and smoothness in a balanced pedal stroke -- one without a hitch or hesitation anywhere through the cycle.

In another vein, the bike fitter must also balance the cyclists physical profile (their flexibility, their strength/stability, their movement patterns) with their positioning on the bike.  One common and very simple example of this that I see is when I have to find the correct bar height that will match the cyclist's pelvic position on the saddle -- once we get the right saddle height and have it's fore-aft adjustment set (we've determined that optimal position of the hips relative to the feet) everyone's pelvic position (and spinal mobility) will dictate where the most balanced place will be for the handlebar placement.

5.  Small corrections!  Bike Fitting is a task of the millimeter, not the inch. -- I am continually amazed at how pronounced even very small changes to contact points can make such a measurable and drastic difference.  Sometimes you need to go big, and when you do, you need to make sure it's not causing other problems, so make sure it is easily undone or walked back if problems arise.

6.  Any bike fit worth it's money needs to be dynamic -- forget the plumb lines, goniometers, and tape measures.  You need to be looked at and have the measuring take place while you're pedaling.  Stopping your pedal stroke to measure -- bad!  Video assessment is fair....using it to "look"  that is, not measure.  The margin of error on measuring with video is on the order of +/-10%, so it's sensitivity is less than exceptional, but a skilled eye may be able to use it to pick out a few problems (see #7 for more).  The infrared used in the Retul system is ideal, since it's dynamic (it measures you while you pedal) and it's hyper-accurate (+/-0.2mm), and measures in all three cardinal planes (thus it renders lateral movements as well) it's the gold standard for measuring.  Notice that I said it was the best way to measure -- having this technology doesn't guarantee a good bike fit.  Since all the Retul does is provide data (very good data), it's still necessary to have a skilled fitter interpret the data.

7.  The trained human eye is a very good but limited tool. -- I'll go on record as saying that it is very important that a good bike fitter does use their own eyeball to help make decisions.  No one should rely entirely on a machine (like the Retul) when performing a bike fit, and the trained eye is great at picking up when something is wrong -- or right.  The trained eye may not be able to tell you what is wrong/right, by how much, and even in what direction something is deviating.  It's great at recognizing patterns or subtle hitches, and at this point in my career one of the times I always use my eye as the final arbiter of when we're done or when we have more work to do.  The machine should never make decisions -- it should only measure a provide data with which to make a decision.

8.  There are no "Have To"s -- There is a lot of bike fitting mis-information out there.  Some written, some just passed along in the verbal tradition from cyclist to cyclist and much of it is pretty bad.

You can see your front hub above/behind your handlebar when you're on the hoods?  Terrible.

You're knee doesn't fall directly over your pedal spindle in the 3 o'clock position?  Ugh, you're in trouble.

These are just two of the many old wives tales and urban legends of the bike fitting world.  There are no absolutes in bike fitting -- sometimes it's in the best interest of the cyclist to have a part of their fit fall outside of the "normal" parameters.  Pick whichever cliche you'd like:  we're all different; no one is completely normal; we're all individuals.  Not everyone falls within three standard deviations of normal, so why do some bike fitters try to wedge everyone into the same box on the bike.

9.  Formulas don't work. -- For the same reasons of individuality as mentioned above, no formula can take into account the vast differences  that exist among cyclists.  Even among similarly sized and built riders, you'll find significantly different optimal fit positions.

The Tri Bike Conundrum

Most triathletes are gear geeks -- I'll include myself in that characterization.  Perhaps that's a reason some athletes get into the sport, and the sport does not disappoint.

While there are numerous geegaws and doodads for the swim and run portion, the bike reigns supreme.  Aero bars, helmets, hydration systems, powermeters, skinsuits, GPS, carbon wheels (including the ominous sounding disc wheel -- you'll know what I'm talking about if you've ever been passed by someone with one), not to mention the increasingly over-engineered bike frames.

With all these options for countless ways to spend your money, what should you spend your money on if you want to get some bling but do it in a half-way meaningful way.

Most triathletes do their first races on a road bike that may or may not have aerobars on it.  Once they invest in the sport, the dedicated tri bike is usually the first big purchase, often followed by the aero wheels, then perhaps a bike fit, and then a good aero helmet.

This sequence is all wrong, though:

1.  Bike
2.  Wheels
3.  Fit
4.  Helmet

I've been doing a lot of triathlon bike fits recently -- I did about half a dozen in one day a few weeks back -- and a number of things struck me while I was doing them.

First, something I always think about when I do any fitting, which is usually that many of my clients would be a lot better off if they had called me and started the fitting process before they bought a bike.  A fit session where we determine the correct position and work backwards from that to determine the right size would save a lot of headaches.  While I do sell bikes, of course, my clients will tell you I never pressure them about my bikes when doing a fitting.  If they're interested in a BMC or a Wilier road or tri bike I'm happy to make that happen for them if it's going to be the best fit.  If they're more interested in another bike from another manufacturer, I'm more than happy to help them get fit to that bike and just take my normal fitting fee.

On this particular marathon day of bike fitting, half of the clients I saw would have been better off on a different size frame.  It all comes down to compromise -- when the bike isn't sized right we have to make compromises in handling, aerodynamics, balance, etc. in order to get it to fit half-way decent.  I may be able to get a functional fit for someone on an aggressive and aero bike like the Cervelo P4, but the compromises we make to get this position can often negate the benefits of that slippery frameset.

I don't think it's a travesty when clients come from a bike shop purchase and aren't fit properly -- that's not really what the shops are good at.  They're good at building, selling and repairing bikes, not analyzing complex biomechanics.  But I do think it's nearly criminal when they are sold a bike that is the wrong size entirely.  Spending thousands of dollars on something that's the wrong size is the ultimate bummer.

For all my tri/TT clients whether they're on the right size bike or not, I wonder whether the super-aero frame is really giving them much edge?  How much edge does the frame give?  What many athletes are surprised to find is that for aero advantage the biggest savings is from refining their body position -- your body supplies 80% of the drag while on your bike.  That bike fit is looking even more important, isn't it?

So what's the next biggest savings?  Must be the frame, right?  Wrong.

Gotta be the wheels then; we're always hearing about how important the wheels are, huh?  Wrong again.

Actually it's the helmet.  A good aero helmet, and it's proper positioning (read as "you need to be in a position on the bike such that you can have the aero helmet properly aligned -- usually with the fin running close to your back"  -- bike fit again) is more critical than the frame or wheels.

Seems crazy, I know.  So I always then wonder, how many of these athletes would be better off on a custom tri bike?  I think the answer is the majority of them.  Even with the understanding that there are few full custom aero bikes out  there, and the ones that are out there are quite pricey -- it's not unusual to have those framesets start at $4,000-$7,000, which kits out to roughly $6,500-$12,000 for a complete bike.  The non-aero custom cousins made out of titanium and even steel, however can be significantly cheaper (and can even provide options for travel bikes with S&S couplers, since triathletes famously travel quite frequently to races all over the world and pay expensive shipping or airline charges to get their bikes there).  The steel and titanium bikes don't have the aero tubing, but with the relative unimportance of the frame's aerodynamics especially when weighted against the extremely important notion of proper body position, which the custom bike can refine without compromise, this is a very easy trade-off.

Am I going to convince everyone to forego the bladed shapes of the stock carbon tri market?  No way.  And I'm not trying to.  There are some athletes (however few) who will be able to fully take advantage of the position those bikes provide, and they should buy those bikes.

But those aren't the clients that need me anyway.  The legions of athletes in the age groups that do need my help -- those with more motivation than time or talent (again myself included) are "my people".

Not  conventional, but very effective.  You spend a lot of time and money training and going to races, don't compromise when it comes to the biggest gear purchase you'll make.

Lenz MilkMoney, Rohloff, Belt Drive project

No time to write much yet....have to get this bike to the client.  Pictures will say enough:

walking vs. pedaling and other misunderstood ideas

So the world has gone a little "functional" crazy.  Don't get me wrong, I'm a firm believer in function: functional exercises transfer strength to actual tasks better, functional movement is a very useful standard by which to grade an athlete's efficiency, I even like the idea of form following it.

No, the problem lies in "experts" trying to take a task we could call functional, and trying to relate it to all movement, or trying to relate all movement to it.  For instance:

GAIT

Yep, walking.  It is tremendously functional, in that we do it all the time and is our main mode of locomotion (and if it's not for you then you have other problems, but that is a whole 'nother blog post).

Just because it is this very core activity, does not mean that it applies equally to all human movement.  Every so often, someone tries to equate walking with pedaling a bike.  They may have certain beliefs about why the human body moves the way it does, or maybe more accurately how it's supposed to move.  Most recently, I've discovered they may believe in a certain pedaling principle or style and they try to reference walking (or sometimes running) as a reinforcement of this style.

The clipless pedal deniers often fall victim to this logic.  And let me go on record, AGAIN, as saying I take no issue when someone just would prefer to ride flat pedals.  I say, whatever floats your boat, and there are certainly times when platform pedals (flats) are warranted either due to the terrain, riding purpose, or rider characteristics.  What I do take issue with is hearing or reading (online of course) that flat pedals are more efficient than clipless and conversely that clipless pedals create some aberrant mechanics that cause knee problems (with no actual or even hinted at evidence to support this).

I won't re-hash what I've already written about walking and pedaling's differences -- you can read up on it here.

A new wrinkle I've heard lately refers to pedal float.  Specifically that it is not an actual mechanical movement of the human body and therefore it's aberrant, and you don't want it...don't need it.

Pedal float is the term that refers to the freedom of movement that clipless pedal manufacturers integrated into their pedals shortly after they came into existence, and is characterized by the heel moving in and out (medially and laterally) while the forefoot is attached to the pedal.

The argument goes that the term "float" is one that the clipless pedal industry made up.  And this indictment is true.  As I go back through my Kinesiology and Human Mechanics textbooks from PT school, I cannot find the term "float" as it relates to foot movement.  The reasoning continues, I guess, that since it was made up by the evil juggernaut that are the clipless pedal manufacturers, then it is inherently false, it doesn't exist, you don't do it and you don't WANT to do it.  Most recently, the reasoning continued (hurray there's more!) that because clipless pedals have float, it's all the more reason to use platform pedals since they don't have float.

Let me address that last part first, and I've got bad news for platform pedal users:  Pssst!  You've got float too!  Yep, even with pins in your pedals and shoes with 5.10 rubber on them.

You may not want to hear that your heel moves in and out (medially and laterally) when you pedal as it does with your clipless brethren, but I'm afraid it does.  Five+ years of data from infrared motion capture doesn't lie.

Moving on....the fact that the term "float" doesn't appear in textbooks does not mean that the movement is a made up one.  For instance, if I say that the movement of the radius around the ulna (bones in the forearm) when we do a push-up is called.........let's say.......the "jablonski motion" (named after a kid I knew in high school -- and one of the nicest people you'll ever meet too) you would be correct in saying that I did in fact just make that term up -- cuz I did.  But it doesn't actually negate the fact that there is this motion happening.  That's the great thing about facts (and therefore science) -- it doesn't matter if you don't believe IT's happening....IT doesn't care, and IT will continue to happen whether you like IT or not.

So FLOAT, right?  It doesn't exist?

Actually it's just a name they have given to a motion that can comprise hip adduction/abduction, tibial rotation, midfoot pronation/supination, ankle inversion/eversion, and a few others that are even more complex (like the movement about the transverse arch in the forefoot -- there 's more than one arch in the foot believe it or not).  So despite the fact that the word "float" is merely a simplification to refer to the action your foot and lower leg move through when you pedal doesn't mean the motion doesn't exist.

Lastly. let me address this false idea that clipless pedals are, by their nature "non-functional" and a "crutch" and that they therefore create mechanical strain about the knee and injury.  Actually if you believe that you shouldn't have the float of clipless pedals you are negating the very real world reasons clipless pedal manufacturers incorporated float into their pedals:  Back when all racers used toe straps ( a precursor to toe-clips) the most competitive were looking for more aggressive ways to secure their feet to their pedals.  Some drilled their shoes into the pedals, strapped them, taped them, anything to get a more secure fit so they could push/pull or fore/aft their pedal stroke to eek out more watts.  The problem was the fewer degrees of movement they allowed themselves (i.e. the more restrictive their fixation technique) the more likely they were to experience knee pain or other biomechanical stresses.

 Hence, clipless pedal manufacturers built in a little float to relieve the strain on the joints above the feet, but specifically the knee.  Speedplay went the farthest by allowing the most free ranging float -- it almost feels like your heels are on ice, they can slide all over the place, which is fine for some, but, I think, goes too far and can create problems for other riders.

So, again, be very careful about what you read, there are a lot of "just enough knowledge" people out there (as in "just enough knowledge to be dangerous").  Figure out what works for you.  If that means you're more comfortable with flat pedals, then go for it.

Happy riding.