Tag Archives: center of gravity

The biomechanics of running backwards.

Not long ago I wrote a post about the benefits of running backwards. This post is a follow-up, discussing the biomechanical and structural reasons that running backwards addresses so many of the typical muscular imbalances that lead to back and knee pain.

It is my firm belief that mere training tips don’t constitute real answers. As with all forms of training, running backwards only does what it does because of how it develops certain mechanical systems and components. It is important to know what those components are or how they are developed, in case we’ve discovered a new and amazing way to “beat” the mechanical requirements of a technique running backwards—therefore precluding ourselves from reaping the benefits of our training.

Problems at the knee can be addressed by looking at the hip or even beyond, because the knee, like any other part of the body, doesn’t exist in isolation. When we push against the ground, the same amount of mechanical energy (the reaction of our action, according to Newton’s Third Law) flows into our body.

That’s why it’s a requirement for all of us, regardless of race, creed, or nationality, to lead with our hips as we throw a punch. Kinetic energy travels through the knee in a straight line, and if a lower or upper muscle doesn’t pull correctly to align the knee with this vector, we will experience knee pain.

Continue reading The biomechanics of running backwards.

Running Backwards: a training idea for runners with lateral knee pain.

The exercise of running backwards helps the runner fix quite a few of the most common biomechanical problems, such as lateral knee pain, certain kinds of lower back pain, and plantar fasciitis. It does this by correcting the location of your center of gravity (CoG).

The CoG is importantly related to the body’s “mechanical solution,” the algorithm of muscle contractions that maintains the body erect and stable throughout the course of activity. Because the CoG is defined as the place where there are no forces acting on the body, any shifts or changes in the muscle firings that the body interacts with mechanical energy—any change in the mechanical solution—will necessarily alter the location of the center of gravity.

Strengthening a muscle that was previously too weak to be used in strenuous exercise will change the body’s mechanical solution: for any particular action, employing more muscles instead of less facilitates the body’s movement through space, since the brain is better able to correct for a center of gravity that moves due to change of direction, change of speed, or variable terrain.

Continue reading Running Backwards: a training idea for runners with lateral knee pain.

The “hip complex:” The reference point for the center of gravity.

Most of us know that when we run (or just walk around), our weight should be on our hips. This allows us to move faster and more powerfully, and to prevent injury. It’s also often said that the hips are the “center of gravity.”

skeleton m
The “center of gravity” is represented by the red dot.

All this is completely true. But what does “center of gravity” mean, anyway?

The “center of gravity” is the point in a body around which the resultant torque (or “resultant force“) due to gravity and other sources of mechanical energy vanishes. In other words, all of the forces that are generated by the body, as well as their interactions with the earth’s gravitational field, all get canceled out at the center of gravity.

The resultant force. This isn’t a commonly used term, but it’s one whose implications we should understand if we want to become safe, effective runners.

Continue reading The “hip complex:” The reference point for the center of gravity.

Tight leg adductors: a common problem, its possible source, and some tips on how to address it.

Over on Facebook, R.B. asked me:

Recently, I’ve been unable to go running for more than 15 minutes without experiencing discomfort in my right knee (my dominant side). Even jumping causes some minor pain. It cracks a lot when I flex and extend it; so does the left side but not nearly as much as the right. From my preliminary research on the matter, I think I have “runner’s knee.” It may have to do with how hard I was training for a while (2x a day, running, weights, parkour, etc.) and then suddenly stopped the intensity for a couple of months this summer when I went to Brazil. Now that I’m jumping back into it, it’s been surprisingly difficult to find the right balance. Anyway, I guess my question is–do you have any suggestions (ie. exercises, readings, whatever) so I can get back to running while minimizing the likelihood of injury? I would greatly appreciate it

Before we begin, a standard disclaimer: I am NOT a physical therapist. I happen to know a lot about the body and I’ve solved this particular problem for myself and others. R.B., I would suggest that you consult a clinician, and take my advice with a grain of salt. That said, let’s go at it:

R.B was referring to a cracking on the inside of her dominant leg. This is most likely a malfunction of one of the muscles that connect the inside of the hip to the inside of the tibia on a spot called the pes anserinus, or “goose foot.”

Note that this is happening on her dominant side.

Let’s think systemically about this: Why is this happening? What problem is the body trying to solve?

Because the dominant leg is the one that supports the most weight, the body wants to bring it further in towards the center of gravity, i.e. towards the midline of the body. Imagine that you are supporting a wooden beam on two columns, but one is strong and one is weak. You’re going to want to put the strong column closer to the center, to support more weight. That’s exactly what the body is doing here:

It’s putting too much weight on the dominant leg because the non-dominant leg is too weak.

This is an example of a systems thinking concept: Shifting the Burden.  (In this case, the burden of supporting the body in an upright position is shifted from both legs onto the dominant leg). 

In order to manage that added burden, the body overuses the adductor muscles of the dominant leg, (which pull the leg towards the midline). And because the dominant leg doesn’t come out much (because it has to stay in to support the weight of the body), the abductor muscles, which pull the leg out, get very little work.

So, what happens is that you get adductor muscles which are too tight, and abductor muscles that are too weak.

Now, there are two answers to this question, and BOTH are important. The first answer is global: the system is developing a strategy of how to perform the function that R.B. is asking of it, and it’s putting too much weight on the dominant leg in order to perform that function. These kinds of sub-optimal strategies are what my favorite biomechanics bloggers, The Gait Guys, call a “compensation pattern.” As they like to say:

What you see in someone’s gait is not their problem, but rather their strategic compensation around the problem”

Let me reiterate that R.B.’s dominant leg had tight adductors because her non-dominant leg was carrying too little of her entire weight. In other words, the problem is that her non-dominant leg—particularly, the extensors and abductors on her non-dominant leg—are probably not strong enough. (In other words, the same analysis that we did within the same leg can be tentatively extrapolated to the entire body): If a set of muscles on one leg are too tight, the opposite set of muscles on the other leg will be too weak.
 
The second answer is local: It has to do with the adductors of the dominant leg. I’m going to post a video about how to train the adductors for this kind of problem in a few days, so for now let’s talk about ways in which we can solve the likely global (systemic) problem.
 

In order to see the most likely systemic problem, we have to cut across the whole body: if the muscles on the front outside of the dominant leg (abductors) are too weak, it is likely that the muscles on the rear outside of the non-dominant leg (primarily the extensors but also probably the abductors) are also too weak. Let me be clear that these are just the most likely culprits. It’s impossible to know specifically without looking at your particular case. The job of the muscles I mentioned is to hold up the leg—the very task that the non-dominant leg wasn’t doing well the first place.

R.B., I can’t give you a specific exercise for your non-dominant leg. That would be irresponsible on my part. But I can give you a general one:

The Gait guys have a cool abductor\extensor exercise that I think would be useful in your case (for your non-dominant leg). Here’s the link to the video.

What you could also do is this: during the same period (say 2-4 weeks) you are training the abductors of your dominant leg, also jump rope for a few minutes in the way I suggest. However, since you want to strengthen the extensors/abductors on your non-dominant leg, I would suggest that you emphasize jumping on your non-dominant foot. By that I mean that if you jump rope (with both feet) for a total of 6 minutes, jump 30 times on your non-dominant foot every minute.

You DON’T want your muscles to get too tired while doing this; you just want to get the non-dominant leg used to the motion of carrying your body alone.

Especiallyyou want the extensors/abductor muscles of your non-dominant leg to develop along with the abductors of your dominant leg. 

You should ensure that the relative strength of both relevant muscle groups stays constant, or you’ll create another compensation pattern.

Also the reason you want to jump rope during this period is to ensure that the strength is being incorporated into a motion pattern. It doesn’t matter how strong any of your muscle groups are if your body doesn’t know that they should be used as part of the holistic motion pattern. Getting them this motion pattern will allow you to eventually succeed on this task.

The best way to get the most bang for your buck out of this would be to jump rope after the training session for your dominant-side extensors/abductors. That way, they’ll be activated and slightly tired when you jump rope, so your body will be able to incorporate them into the motion much more easily.

Please put your questions in the comments; I’ll address them there.

Thanks for reading!

UPDATE: If something about running is difficult for you, or it’s difficult to get started running, there’s a comment thread going here.