Tuesday, September 25, 2012

Open joint vs closed joint lifting – Part 2

In part 1, I talked about the concept of the open joint lift and how it can be used to move big weights. This post will be about taking that concept and using it to manage and prevent injuries at the knees.

When talking about loads on the body, there are two kinds that we will worry about: compressive forces and shear forces. Compressive forces can be described as putting a load on your back, such as a squat. The weight pushes you down into the ground. Shear forces are a bit more confusing. The easiest way to think about shear forces is to imagine a joint moving further away from the mid-line of the body. An example would the leg extension machine. The knee and ankles are far away from the mid-line of the body, and this would put a lot of shear stress on the knees. Our body can handle a lot more compressive force than shear force. As proven by Stuart Mcgill, “the spine doesn't buckle until 12,000-15,000N of pressure are applied in compression, but as little as 1,800-2,8000N in shear will get the job done” (Cressey). This same idea applies to the knees. It’s very rare to see somebody who has knee pain when squatting get the same knee pain when standing up with the weight. It goes to follow that the more open the knee angle is, the less shear stress on the knees. This is why a deadlift will almost never hurt an injured knee, while a full squat will kill a person’s already injured knees. (Note: I am not bashing on the full squat, some people find that it helps their knees, some find that it kills their knees. More often than not, I find that it kills a person's knees. Your results may vary.)

Andy Bolton with 1000+lbs, spine not collapsing yet

Another way to determine if a leg exercise will create a lot of shear force is to determine shin angle, or knee travel. In a full squat, the shin angle will be as acute as it can possibly be, while in something like a box squat the shin angle will be more perpendicular. The more acute this shin angle, relative to the feet, the more shear stress will be placed on the knees. The above principle still applies - the knee is far away from the midline of the body. This is also a reason why people with long femurs will find squatting painful, their knee has to travel a lot further than a person with short femurs.

So how do we use this information to keep our knees healthy and pain-free? Here are some guidelines:

1) The obvious solution: strengthen the back of the body. The reason knee pain is so prevalent in today’s society is that people are just plain weak through the posterior chain – the lower back, glutes and hamstrings. These muscles are very important when it comes to preventing back and knee injuries. The quads pull on the patella and if the hamstrings and hips are not strong enough to offset that pull, there will be problems. Ok now that we’ve got that out of the way…

2) Use the open knee angle to work around the knee problem. The conventional deadlift is a great way to strengthen the back of the body and stay pain free through the knees. Other exercises that work great in this regard are the box squat and Romanian Deadlift. They both (done right) involve very minimal knee travel and so place very little shear stress on the knees. Great for rehab and for getting stronger with bad knees. 

Notice the shin angle

3) Give up squatting for deadlifting variations. Hear me out before you form a pitchfork mob. Squatting will always entail a more vertical spine than a deadlift. This automatically makes the knees travel. Deadlifting during a bad knee period will provide the same training stimulus on the legs, and make sure you remain strong during the injury. Chances are you will come back from the injury with a stronger posterior chain and climb to a higher squat.

4) Front squat or low bar squat in the presence of knee pain. They both have been shown to reduce shear stress on the knee, and will give you a squatting stimulus.

5) Stay off the leg machines. The leg muscles are never meant to activate in isolation, and forcing them to do so will lead to problems down the line. Using these machines once in a way, or in addition to compound movements on the feet like the squat and the deadlift is fine. Exclusively using them is not.

6) Deadlift. Seriously.

Less shear stress than the back squat
The next part will be about the spine and how to use the open concept angle to prevent and manage back injuries.

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