What 5 variables would I explore for a rider with anterior knee pain?

If a rider is experiencing anterior knee pain, there are five things I’d look at first, and invariably in the same order each time.

In the medical world, doctors are very aware that multiple problems can cause the same symptoms, so they play the odds and test for the most common (or most likely) cause first. As bike fitters we should be doing the same thing, making it clear to our clients that if the first measure doesn’t fix their problem, we have other things to try and other variables to consider.

It’s important to distinguish between most common and most likely: To continue the healthcare analogy, a patient might be showing signs of the common cold or ‘flu, but those symptoms could also indicate a tropical disease transmitted by mosquitos. If you’re outside of ‘flu season and the patient has recently travelled to somewhere tropical, maybe the latter is less common but more likely. In bike fitting, distinguishing between most common and likely is just as key; a good rider history and physical assessment can help you make similar decisions about what is most likely to resolve your client’s issues.

I’ve written about identifying variables before, so I won’t spend too much time on it here, but if I had an athlete with anterior knee pain I’d start by looking at cadence/gear, crank length, and seat height as my first potential causes. All of these have logical mechanisms behind them.

If the rider is mashing a big gear (low cadence, high torque) then the loads through the joints will be higher. Encouraging them to drop to a smaller gear and spin a little more could be enough to solve the issue. But if the rider is already spinning smaller gears, then because I know the mechanism, I know that the gearing isn’t the cause. So, I’m not just going to blindly suggest dropping another gear and increasing the cadence further.

Likewise, if the crank is quite long for their leg length, and I won’t get into the different ways to identify optimal crank length in this blog, then they could be bending their knee significantly at the top of the pedal stroke. As the knee bends more, and approaches 115 degrees of flexion, which is possible with short riders on proportionally longer cranks, the contact area between the patella and the femur decreases in size. Pressure is force divided by area, so if the area decreases then it’s logical that the force increases.

Another reason that pressure could increase is the mechanical direction of the force being applied. When the knee is less flexed, in walking for example, the contraction of the quads pulls the patella vertically, so the force isn’t pushing the patella directly into the femur. In cycling, when the knee is flexed to 115 or more, the quads are pulling the patella more directly into the femur, so the direction of the force means that it’s more effective – think pushing down on the pedal at the bottom of the pedal stroke vs pushing down on the pedal at the front of the pedal stroke: the force has a much bigger impact when it’s applied in the right direction.

So, if my rider had a lot of knee flexion at the top of the pedal stroke, I know there’s a mechanism there that could cause increased patellofemoral pressure and may increase the risk of patellofemoral (PF) pain. But what if they don’t? If maximum knee flexion is 112 or below, then I’m probably not overly worried about it. So, I’d move on to the next variable, which in this case is related.

If seat height is too low, then it could also contribute to more knee flexion and increase risk of PF pain for the same reasons as crank length. But in this scenario, we’re assuming that knee flexion doesn’t exceed 112 degrees, so we’re happy to tick this one off as well.

With no obvious cause through these first three common triggers, I’d move on to the next two, which are a little more difficult to tease out. Firstly, where does force onset occur? By that, I mean where do they actually start pushing on the pedals? It doesn’t matter if their knee angle reaches 115 degrees if they don’t start applying force until the knee has extended to 110 or less. Smaller riders often have longer proportional cranks, but they don’t all experience anterior knee pain. That could be because they naturally delay force onset or could simply be that the absolute force being produced is lower than that of a bigger rider while bone density and resistance to PF pain is probably similar.

The final piece that we’re going to discuss here is probably one of the most difficult to measure without force pedals or a very good power meter; are they pushing forwards across the top of the pedal stroke? To a certain extent, it’s related to the previous point about when force production occurs, but it’s also a standalone issue that needs to be understood. If, at force onset, the rider is trying to push down and away, then it could be a glute dominant activity (assuming there isn’t so much hip flexion that the glutes are outside their optimal range for force contribution). But if the rider is pushing forwards at that point, then it’s almost definitely a quad dominant activity. A quad dominant activity at high levels of knee flexion would increase those PF forces and be a logical mechanism for PF pain.

Without force pedals or directional force data, it can be difficult to identify whether or not forward forces are being applied to pedal through top dead centre (TDC). But you can often ask the rider if they’ve “learnt” a particular pedalling style because anyone that’s been told to pedal in squares, or push forwards across the top of the pedal stroke and backwards along the bottom, is probably at a higher risk of PF pain.

Obviously, there will always be a rare case where none of these things work and you have to explore other variables, but I’ve found this approach to be very helpful and effective more often than not. It’s logical and uses scientific principles, unlike the old approach of simply moving the saddle backwards.