Forward Lean, Knee Pain & Lever Arms

If you’ve ever read some of my other blog posts, you would know that I loathe the prescription of “make sure you lean forward when you run” promoted by all the “one size fits all” proprietary running techniques out there (Pose, Evolution, Chi etc)

I firmly believe that running technique is uniquely individual, as demonstrated by the following post…

While I can’t stand the often promoted “forward lean” instructions for running, there is a time and place for it.  For example, when a runner is suffering from knee pain – more specifically, patellofemoral pain syndrome (PFPS), a forward lean maybe justified…but not necessarily.  This post gets a bit detailed at times.  If you get confused, consult this video – it may help explain.

There are many factors to consider when a runner is suffering from knee pain (more specifically, “PatelloFemoral Pain Pyndrome – PFPS).  One of the biggest factors is the stability of the hip in the transverse plane (i.e internal vs. external rotation).  However, I plan on making a post on that at a different time

Anyway, I digress…

The point of this article was to talk about PFPS and the “forward lean”.  One of the many factors to be considered is trunk position.  Recent research has shown that an increased trunk flexion angle angle (bending forward) can be associated with a decrease in knee extensor moment which results in less compressive force on the patellofemoral joint (a joint in the knee).  Keep in mind, the forward lean reduces the extensor moment, but doesn’t change the knee flexion angle. (For those about to get mad at me for using “bending” forward and “leaning” forward interchangeably, I find that most people who are told to “lean” forward end up “bending” forward anyway.  More on that later…)

So, why does bending/leaning forward reduce the strain on the patellofemoral joint?

Well, very briefly…there are two competing ground reaction forces that are contributing to the external flexion moment at the knee (a force causing it to bend):  1) the vertical ground reaction force and 2) the anterior to posterior ground reaction forces.  Essentially, when you land, there is a vertical force being applied to the knee because your body is going downward when you land, and there is also a posterior force being applied because you are also going forward when you land.  The quadriceps exert an extension moment in order to combat the two external flexion moments that are being applied.  Hopefully, they sort of cancel out and the knee doesn’t buckle.

Unfortunately, the extensor moment at the knee that is exerted by the quads also puts a large load on the patellofemoral joint.

In order to reduce the extension moment on the knee from the quadriceps you need to move the load somewhere else.  In this case, by bending the trunk forward, you move the center of mass more forward (closer to the knee), thus reducing the moment arm for the body’s center of mass force on the knee. In this case, you move the load from the knee on to the hip and low back.

So, here’s the caveat.  If the objective is to reduce the moment arm for the body weight to the knee, is leaning forward the best strategy?  Well, maybe for some, but certainly not for everyone.

As you can see in the video, the lever arm for the knee is reduced by leaning forward, however, the lever arm for the hip and the low back muscles is increased, thus increasing the load for the glutes and the low back muscles.  Unfortunately, this is not mentioned in a couple studies that found reduced load on the knee by leaning forward.

It’s a trade-off.

I have included this video to help explain thing – perhaps if is more clear on a video…

Next time someone tells you that you should “lean forward”, please explain all this to them, or refer them to this blog.  If you want to reduce the lever arm from the cernter of mass of the body to the knee, another strategy would be to not overstride.  Landing with the foot closer to the center of mass, I think, may be a better strategy.

In the end, there are various ways of dealing with injuries and performance.  If you think that getting a gait analysis at a local store that sells shoes, or using your local running coach is a good idea, you may be in for a surprise. Can they explain moment arms, force vectors?  Do they understand detailed anatomy and the functional aspects of it?  Do they read research, or do they read blogs?  Do they have a “one size fits all” approach?

  Sorry if I seem harsh, but I’m getting tired of clients telling me they’ve gotten a gait analysis done, only to find out it was from a source who knows nothing about anatomy, or biomechanics, but they are a “good runner”.  I hope you don’t take your broken car to someone who is a “good driver”, but knows nothing about how a car operates.



3 Comments so far:

  1. Mike Andersen says:

    The argument here is not really about the ‘lean’ per se. Most of those people preaching the lean are getting the dimensions wrong. I teach my runners to look for a lean from the back of the heel to the front of the chest, hardly the bent over image you show. This lean is achieved by landing under your center of mass and the lean is less a lean and more of a positioning idea. This leads to less extended knees on impact so the goal is still achieved of a more efficient gait. I think the problem with all the methods is to protect their terminology that makes them unique and to not worry enough about helping runners stay injury free. I do like your sprinter example (or whoever you quoted, can’t remember) but I think using sprinting is not an equal comparison. I’m new to your blog and really enjoy the article. I guess even my argument is all semantics. You could potentially draw a line from the ground up from a random point on the runner and say this one’s a lean and this one’s not. But the point remains, the lean can be a part of healthy gait if done right. I guess not using ‘lean’ as the term and rather angle might be more beneficial. Would love critical feedback, since I guess I am one of those people who reviews runner’s form and provides shoe feedback that you judged. I do however read blogs, study research, attend conferences and my fiancee has just finished her grad research on heel vs. mid strikes in patella femoral knee pain but I digress. Looking forward to hearing from you. Great work though. -Mike

  2. […] Various potential problems with this advice have been discussed here and here. […]

  3. […] Here is a sampling of some of these videos: 1) Tendon Compression: Tendons are particularly vulnerable at sites where they wrap around and are compressed by bony protuberances. During the initial stages of treatment, it is often important that patients understand this concept and try to avoid positions or exercises that may increase the compressive load. 2) The Science?? of Prescribing Running Shoes: As referenced above, this is one of the more common question I get. This should be a patient friendly version that everyone can understand. 3) Increasing Anterior Ankle Impingement by Limiting Pronation:  This video is embedded in this blog post.  I am frequently encountered with patients suffering from anterior ankle impingement and they are running in zero drop shoes or shoes that limit midfoot pronation.  I use this video to explain why this is probably a poor choice. 4) Craigs Test:  Explaining the idea of femoral anteversion isn’t easy without some visuals.  This video accompanies this blog post. 5)  Hamstring Tension During Running:  This is a video explaining various factors of sagittal plane position of the pelvis will affect hamstring tension during running. 6)  The Forward Lean Reducing PFPS Forces:  This study reports that increased trunk flexion angle will reduce patellofemoral joint forces.  While this is true, this video demonstrates an alternative.  This video accompanies this blog post. […]

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