 So welcome back or welcome to the 13th edition of the RCA Training Tips Show. Now before we get into this video and talk about why shims have a bad name, according to a few, you might have clicked on this video and thought, what the hell is a shim? Well, according to Google and Steve Hogg's website, a shim is a means to lengthen a functionally or measurably short leg while cycling. A shim stack may be needed as a short term, medium term or permanent fixture. And as you can see on my right shoe, I now have a six millimeter shim. Now before you click off this video because you think you have perfectly symmetrical legs, you may be interested to learn that I rode for 11 years thinking my legs were perfect and guess what, they're not. Additionally, Neil Stambry, who is the expert bike fitter we'll be talking to in this video about shims, tells us that over 70% of cyclists that leave his clinic leave with a shim in their shoe, which just might beg the question, are your legs perfectly symmetrical? Because if they're not, you'll certainly be inefficient on the bike. You'll be losing power and there's a fair chance you'll be causing injuries if you already have not. Now before we get into the discussion with Neil, just know that this was the question I posed to him as we begin the discussion. So Neil, after our previous video we made together where you fitted a shim to my shoe, I had quite a number of people reach out to me talking negatively about shims. So why is that? Now before Neil responds and we get rolling in this video, just know that I've been using a shim on my right shoe for about a couple of months now and I've experienced one negative when it comes to the shim, which is a question I posed to Neil towards the end of the discussion. So let's get into it. Yeah, all right, yeah. So I guess the simplest explanation is if you're, it's human nature to extrapolate from our own experiences. This is how we learn a lot of things. So let's say for example that you've got a rider who's dropping their right hip and they think they may have a shorter right leg and they whack a shim under there and it makes their right knee hurt. The tendency is human nature. The tendency is to extrapolate that out to shims are never a good idea. So you tar every situation with the same brush and we're all kind of guilty at this at some level. It's a common psychological trait is we extrapolate from our experiences. So I'm guessing that those riders have tried a shim or been given a shim by someone and for whatever reason it didn't work for them. So they believe that shims are always a bad idea. It's because I do this 10 times a week, fitting shims to riders I mean and not fitting shims to riders. It's just been my experience with hundreds and thousands of people that shims as a tool to compensate for a structurally shorter leg or a functionally shorter leg seems to be the best option. And it's not the greatest option of course is to make that person perfectly symmetrical in every other sense. Neurologically, muscally and skeletally and then you won't need a shim. But we can't break your leg and make it longer. That's probably against the rules. You know, I'm sure there's a law against that. Expensive operation too, yeah. They do it in Russia with the supermodels. Yes, you can have your legs broken and they put a brace around it. You've really looked into this, haven't you? I've looked into this, yeah. So it can be done. It's very unpleasant and you spend a lot of time on your back with pins in your leg. So we can't really do that. And how many people, I mean before you continue, sorry to interrupt, but I want to understand, because you said last time there's quite a strong percentage of people that you examine that do have a leg length discrepancy. So roughly how many people would it be that you see? I reckon it's about three quarters to 85 or 90% of people leave my clinic with a shim. And often it's really small. I'd say probably 75% to be safe. It doesn't necessarily, someone pointed this out in the comments of your video, I think I read it, and they're right. It doesn't necessarily mean that that leg is structurally in the bone shorter than the other one because it could be a functional leg length difference or a mixture of the two, which is very often the case. If you function your whole life with a six millimeter shorter leg on your right side, invariably you develop some muscular asymmetries from that, which then exacerbate the leg length difference. So one of your hamstrings will be bigger and stronger than the other and the opposite quad will be bigger and stronger. So some of this six millimeters, for example, in your shoe, you may only have a four millimeter shorter leg, but because you're muscally imbalanced to a small extent, you require six millimeters to not drop your right hip down and forward. And if that's what it takes, that's what it takes. There's no point in me going, oh, Cam, I believe that your leg is only four millimeters shorter, so I'm just gonna put a four mil shim and leave you dropping your right hip and your left knee will still hurt or whatever is happening to the person. So we have to take that person at face value when we see them. And especially if you whack a decent shim in like this, you wanna see that person a couple of months later. And sometimes the shim height goes back down because they're much more symmetrical in a muscular sense than they were. So you drop two mils out of the shim, oh, you know, your quads have evened up, your hamstrings are getting in. My quads are uneven, by about three or four mil, yeah. Yeah, yeah. It's a classic adaptation. So if that evens itself out in the next few months, this may long-term end up at a four millimeter height or five or something. There's also a chance it'll get bigger, which happens occasionally. So, but on the day that we see the rider, they're looking for a result, they're looking for symmetry, which stops their knee hurting or whatever it is. And if it takes a six millimeter shim, well, you know, I can't definitively say that your leg is six mil shorter than the other. But on the day that I saw you, it was, it was acting six millimeter shorter than the other. So shims tend to be the best solution to leg length discrepancy. Some people will advocate staggering the cleat forward. Yes. And this does work very occasionally. Maybe one in 50 or one in a hundred people with a structural difference, it'll be the best way around the problem because for whatever reason, they don't cope with the shim for other reasons. But it's extraordinarily rare that that's a better way to deal with the leg length difference. As you shuffle the cleat forward, it does effectively make that leg longer, right? It creates a longer distance between the pedal center and the pelvis up higher up the chain, which is great, it lengthens your leg, lengthens your shorter leg. The problem with it is that it creates an asymmetrical amount of foot over the pedal, right? So left and right foot have suddenly got a different cleat position, right? And anyone who's ever tried, you know, putting one cleat five millimeters in front of the other, most of the time it feels a bit off. And that's because you're challenging your central nervous system to try and maintain symmetry by adding extra asymmetry to the position. So it's kind of antithical to what we're trying to do. The rider, as you shuffle the cleat forward, the rider's foot will be less stable over the pedal. So they've got a larger lever arm to try and stabilize the foot over the pedal. So if you took this to its extreme and you shove the tip of the center of the cleat right up under the nose of the shoe, right? That foot would be very unstable over the pedal as it's trying to apply force on the down stroke. So that rider is either just gonna totally lose control of the stroke and just massively drop their heel through the stroke, or they're gonna excessively over engage their calf as an effort to stabilize the foot over the pedal, right? But the important thing is that they will do that differently to the other side, because it's staggered, right? Of course. And that introduces further asymmetry into a system which we don't want to be asymmetrical. So you end up essentially with a stagger in the cleat position, which affects the amount of anchoring of the rider, which then has further effects up the kinetic chain, which in my experience have been a worse solution than shimming the leg, yes. And if another solution is not doing anything at all, and would it be fair to say based off your experiences then that at least 50% of the cycling population would have some type of leg length discrepancy? If you're seeing 75% of people away, if you're sending 75% of people away with a shim, then wouldn't that be maybe an assumption we could make that a lot of people at least have a leg length discrepancy that are currently leaving it. So where does that lead? Yeah, it's a good question. I guess the real question is, do I see a perfect cross section of humanity in my clinic? And the answer is probably not, right? So the people that compensate fabulously for their leg length discrepancy on the bike and have no symptoms, no pain, no nothing from their leg length difference, they don't come and see me for a bike fit. The ones who come and see me, the ones who got symptoms, whether it's a sensation of asymmetry or a pain somewhere, right? So perhaps I'm seeing the people who don't compensate well. Right. It's an interesting, so maybe more people of, maybe everyone's got a leg length difference and some of them just compensate better or maybe it is actually only 20 or 10% of the cycling population who've got a measurable leg length difference. And those are the ones with problems who present to me. Yeah, so I don't understand. Yeah, so that is a difficult extrapolation to make with any degree of confidence. Right, that makes sense. But it's a good question. I've often wondered, you know, Steve Hogg always said to me, you know, we see a skewed sample of humanity. We see the weird people with leg length differences and pelvic torsions and people with structural problems and physical problems because they're the ones who need a bike fit the most. Very good point. Yeah, it's a tough call, mate. Very tough call. So what are the common issues they would face? So if somebody's watching this at home and they are experiencing some issues and they think it could be to do with leg length, what type of issues do they cause? Both on the bike, but probably more so, you know, does it cause injury and what type of injuries? Oh, yeah, yeah, yeah. If it's allowed to go unchecked, it'll cause injury. Most cycling injuries are overuse injuries unless you crash, right? That tends to be a fairly rapid injury when you crash. But chronic overuse injury. So it can be almost anything. A leg length difference as part of a position will cause a symmetry in your motion, which will tend to favor your dominant leg, which in most of us is our right leg. So a huge number of us, when there's a positional challenge or a shorter leg or a seat being too high or anything like that, will drop our right hip down and forward. And that will typically create issues with the plane of motion of the left leg. So I guess most people who have a leg length difference who are having issues on the bike from it, they will typically end up with a left-sided knee, hip, foot, whatever. And it can be anything. It can be a hotspot, which only ever occurs on one of your feet, not on the other. It can be cramps in your calf, which only ever occur on one calf and not on the other. It can be upper hamstring pain, lateral hip pain, lateral knee pain, medial knee pain. It can be almost anything. It just depends on how else that person is built and how well they compensate around their positional challenge, which in this case is a leg length difference that we're talking about. Yeah, you can't say, oh, a leg length difference has always caused lateral knee pain, because they don't, they can cause any type of asymmetrical, compensatory related pain. Yeah, it can be anything. Yeah, okay. You know, I've seen people with, oh, you know, one of my feet goes numb, only one. Is it bigger than the other? No, it's not, it's not. The shoe is symmetrical. Why is one going, it's because they're dropping one hip and loading that foot twice as much as the other. And it's not lifting off at the top of the stroke because that hip is further forward, so the circulation can't get through the bottom of the foot and that sort of stuff. So leg length differences can cause all manner of weird and wonderful one-sided problems. Yes, okay. Now I'll throw one slight negative at you when it comes to the shim from personal experiences. And I say slight, I'm being nitpicky here because what the shim has enabled me to do is I'm sitting on the bike a lot better. I can already feel it, I can sense it. However, when I'm getting out of the saddle, which is probably about 3% of my riding, punching it up a hill, stretching the legs, I do find it a little bit unnatural, the feeling. I feel like I'm getting used to it, but I'm not 100% used to it yet. So is that a common objection that you can get? Yeah, yeah, most people, most people don't notice it too much and they sort of relegate it into the back of their mind and don't worry about it. It's a fairly small thing unless the shim is really big, where it can become a proper issue. But you're exactly right. It's one of the negatives of having a shim. What happens is in your case, you ride with a moderately toe down attitude when you're seated, right? So because of the height of the shim, which is only in your case, six millimeters, it's basically creating a much, well, a six millimeter taller stack height of the cleat is what people would call it, right? Let's say for example, the shim was 10 centimeters tall. It was huge, really, really big, right? That would create a lot of instability over the axle of the foot, right? Which is different to the other foot, which means that you end up with a Steve Hog coin this term and I really like it called rocking torque. It creates different rocking torque depending upon where the foot is rocking over the pedal. So when you're seated and you're pedaling along, your foot's moderately toe down in your case, the cleat position is actually further forward over the axle by a small amount. However, when you stand up and you go like this, it's further forward by a large amount, right? So the more toe down you are as you're springing out of the saddle going up that climb and you point the foot right down, your foot goes way out in front of the axle by 10 centimeters if it's a 10 centimeter high shim. But in your case, it's six millimeters. Now humans are pretty sensitive that you can sense six millimeters. You know, I've tested it on myself. I can sense two millimeters of this because it creates this asymmetrical rocking torque of the two feet, which your brain can sense. So it is a slight negative. The flip side of the coin is it's never gonna cause you a problem. You're never gonna get injured doing a 20 second punchy climb up a hill out of the saddle. It's never gonna cause a massive issue. All it does is create a sensation of less foot over the pedal. So it feels in that instant like your cleat is further back on the shoe. And that's the downside of wearing a shim. And luckily, you don't spend a lot of time out of the saddle as most of us don't. We spend most of our time seated. And this is a very small negative effect of having a shim. And it's far outweighed by the positive. I agree with that. Yeah, yeah. And this same effect sort of occurs if you stagger the cleat, like we go back to what we were saying before. If the cleat is staggered as a weight of dealing with the leg length difference, you'll get the same effect anyway. So you might as well use a shim. Absolutely.