The Mobility-Stability Continuum A New Look At Joint Health by Mike Robertson

Mobility and stability go together like peanut butter and jelly... spandex and cardio... Eric Cressey and Tony Gentilcore.
Over the past few years, gentlemen much smarter than myself have been discussing the importance of mobility and stability at length. Stuart McGill, Mike Boyle, Gray Cook, Bill Hartman, and Eric Cobb all come to mind.
It started off quietly, but this topic has slowly grown to the point where I felt the need to bring the pendulum back to center. Somewhere along the way, we lost sight of the big picture. This may sound weird coming from a purported "mobility" guy, but hear me out.
I want to clear up some misconceptions regarding mobility training and help you to better understand how truly inter-related mobility and stability are. Along the way, we'll find out what other influences (outside of mobility and stability) could be affecting your performance.

Two Sides of the Same Coin

Mobility and stability are complementary in nature. When you strive to improve mobility at a joint, to some degree you sacrifice stability. It works the opposite way as well; the more stable you make a joint, the more you inherently restrict its mobility.
Before we go any further, let's get the semantics out of the way. Here are the Bill Hartman-approved, "simple" definitions:

Mobility — The ability to produce a desired movement.

Stability — The ability to resist an undesired movement.

When examining mobility, the key factors involved include the architecture of the joint(s) at hand, soft-tissue length, and neural control over the surrounding muscle groups.
Stability is created via a blend of active and passive influences. Passive constraints include the joint capsule, ligaments, and the joint architecture itself, along with more active constraints like motor control of surrounding musculature, muscular strength, etc.
Each joint serves a specific purpose — to produce a given movement. Mike Boyle took the concept to another level when he introduced his "joint-by-joint" approach to training. Here's the Reader's Digest recap: It appears as though each joint requires either more mobility training or more stability training.
Even more interesting is that it appears they alternate in fashion. A joint which needs more mobility is surrounded, above and below, by a joint that needs more stability, and the opposite is true.
The chart below depicts each joint's primary need, according to the joint-by-joint approach (1):

Joint — Need

Foot — Stability
Ankle — Mobility
Knee — Stability
Hip — Mobility
Lumbar Spine — Stability
Thoracic Spine — Mobility
Scapula — Stability
Gleno-Humeral Joint — Mobility
Elbow — Stability

This view is beautiful in its simplicity. However, it has led to plenty of detractors, mostly people who hold their own dogmatic views or those who don't fully understand the concepts.
Unfortunately, some people seem to think that the joint-by-joint approach is purely black and white. If the joint-by-joint table says the hip needs more mobility, then dammit, you're going to give it more mobility!

If all you've got is a hammer, everything looks like a nail.

The hip generallyneeds more mobility. However, there are certain individuals who have excessive hip mobility and therefore require more stability. The joint-by-joint approach gives you a base understanding of the movement requirements at each joint, but it can't be applied injudiciously and without first making proper assessments. The chart doesn't replace the assessment, but it speeds things up and makes it more efficient.

It's Easy, But Not That Easy

We'll use the knee as an example. According to the joint-by-joint approach, the knee needs more stability. But in fact, a knee with restricted sagittal plane mobility (flexion and extension) would be at an increased risk of injury.
Instead of broadly saying that we need to stabilize the knee joint, we'd be better off by saying that we need to stabilize it in the frontal and transverse planes, while mobilizing it in the sagittal plane.
Perhaps a better way to state this is that the joints in the "mobility" section of the column have more freedom of movement (in multiple planes) when compared to the "stability" joints. Instead of thinking black and white, we need to think of things in a grayscale fashion.
The Mobility-Stability Continuum
The mobility-stability continuum piggybacks upon the joint-by-joint approach, and hopefully takes it to the next level. It's not necessarily "new," but I hope it'll enhance your understanding of what you already know.
Hopefully we are in agreement that all joints need some degree of mobility andsome degree of stability. The key is to understand how much mobility/stability we need at each specific joint.

Stable				Mobile
Knee	Elbow	Scapula	Hip	Shoulder

If we examine the continuum above, on the left we have joints that traditionally need more stability. On the right, we have joints that need more mobility. If we understand the architecture of each joint, this concept becomes even clearer.
Let's look at the knee and elbow, two joints similar in architecture and function. They should require an equal amount of stability, right? Not quite.
The elbow is comprised of the humerus, the radius, and the ulna. So while you can flex and extend your elbow, the inclusion of pronation and supination via the radius tells us it needs a little bit more mobility than the knee. The knee, even though it canmove slightly into internal and external rotation, should only be trained to flex and extend.
Another example is the difference between the hips and shoulder joints. They're both similar in nature (ball and socket joints), but the femoral head sits much higher and tighter within the joint than the humeral head does.
The hip socket is also much deeper than the glenoid, which accounts for more differences in joint mobility. So while they're similar in architecture, the hip will naturally be more stable than the shoulder.
The trickiest joint, in my estimation, is the scapulo-thoracic joint. I've heard both sides of the equation argued. Some will say it needs more mobility, while others will say it needs more stability. I'm not sure that we need equal training of both, but let's just say we need to understand the multiple functions surrounding the scapulae and train accordingly.
If you don't have adequate stability, it's only a matter of time until you suffer from some sort of rotator cuff injury. Recent literature states that in patients with gleno-humeral instability, their scapula is unstable 100% of the time!(1)
I don't know about you, but I think 100% is pretty damn often. With regard to training, we generally need more stability with regards to scapular protraction, retraction, and depression.
On the other hand, if you don't have adequate mobility in the scapulae (especially into upward rotation), you're again at risk for impingement injuries. In her book, Diagnosis and Treatment of Movement Impairment Syndromes, Shirley Sahrmann ranks scapular downward rotation syndrome as the most prevalent upper extremity issue.(2)
What does this mean to you? Absolutely nothing... if you are cool with never putting your hands over your head for the rest of your life. Bill Hartman and I wrote an entire article about this.
After all, we can get 120 degrees of shoulder abduction or flexion from our gleno-humeral joint, but if we aren't getting that necessary 60 degrees of upward rotation from the scapulae, it's going to lead to issues down the line.

This would severely impact our "raise the roof" skills.

The take home message here is this: Stop thinking about things in black and white, mobile and stable. Instead, think about how mobility and stability work in unison. You can't have one without the other. The key is understanding the architecture of the joints themselves, the soft-tissues surrounding them, and how they're used in motion throughout the day.

Mobility Training vs. Loaded Mobility

Another interesting concept is unloaded or bodyweight mobility training vs. loaded mobility training. Both have their role, but we need to examine them in a situation-specific context.
I've heard a lot of people try to refute Dr. Stuart McGill's claim that the lower back needs more stability. I don't know about you, but when Dr. McGill speaks, I listen. After hearing him speak in Chicago this past year, I'm even more impressed with his understanding of the human body, especially the lower back.
One of McGill's examples discusses how the core is designed to prevent rotation and counteract movement around the lumbar spine. If you look at the anatomy involved, the core (including the rectus abdominus, internal and external obliques, and transverse abdominus) is layered in a cross-hatched fashion that predisposes it to being stable and preventing rotation.
Along these same lines if your rectus abdominus were truly designed to promote spinal flexion, you'd have two long hamstrings instead of your beloved six or eight-pack!(3) Sahrmann agrees with this point as well.
People in the "more mobility" movement have argued that McGill must be crazy and that movement is inherent around any joint. I agree to some extent, but remember that while some movement is necessary, it's all relative! Just because we can get more mobility from certain joints doesn't mean we should.
Bogduk also states there's only about 1-2 degrees of rotation around each lumbar segment, with the exception of L5-S1.(4) In contrast, the upper segments of the thoracic spine have 8-9 degrees of rotation per segment. Where would you rather get your mobility from?
Another example would be the strength trainee with knee pain. For these people, unloaded or bodyweight mobility drills could be very beneficial and pain-free. However, give this same person some dumbbells and have them perform a movement pattern like a lunge, and you could very easily increase pain and irritation while losing training time.
In the end, I can't give you a definite answer like< "You need X amount of movement at each joint." That's just not possible. Instead, remember that our simple definition of mobility is the ability to produce a desired movement.
The gleno-humeral joint mobility needs are vastly different between a high-level pitcher and your average strength trainee. As well, understand that it's not necessarily about more total mobility as it is about optimizing mobility for your given sport.
The key is that strength training should be good for your body. You should be able to move through a full range of motion (ROM) pain-free. If you can't, you need to figure out why, and address it.
Dr. Cobb put this into words for me a while back. "Strength training cements your posture and mobility." Whether that posture is good or bad is up to you. The question is, are you cementing good, clean movement patterns through a full ROM? Or are you cementing inefficient, pain-producing movements through a limited ROM?
Finally, keep in mind that there's a definite difference between unloaded, bodyweight mobility drills and loading that mobility via strength training.

The Problem With Stiffness

Unfortunately, understanding mobility and stability is only part of the equation. The concept of stiffness is one we've only recently begun to understand in depth.
Here's an example of how mobility, stability, and stiffness work together:
I've posted this clip several times now, because it helps me present several key points. Three months before I shot this video, he couldn't squat, lunge, or deadlift without lower back pain. In all honesty, he couldn't even approach parallel on a bodyweight squat without back pain!
In the clip above, his mobility is vastly improved, yet there's still something missing. Many would say that he's still too tight in his hips, and that's true to some degree. But the bigger issue here is the imbalance in stiffness we're seeing between his hips and lower back. Sahrmann discusses stiffness throughout her text, but here's another quick and dirty definition:

Stiffness — Passive resistance to stretching.

Boyle related stiffness to two bands pulling on each other. One band is big and strong (representing our hip stiffness), while the other band is smaller and weaker (representing our lower back stiffness).
Since the bands aren't equal, the bigger band (greater stiffness) is going to force the smaller band to deform more than it normally would. If the bands were of equal strength, pulling on one would create an identical change in the other.
In the example above, Justin's hips are stiffer than his lumbar spine. As he moves into deeper hip flexion, his hip stiffness exceeds that of his lumbar spine, so his low back rounds.
Now we could stretch his hips until the cows go home and get some results, but the better option is to increase the stiffness in his lower back and reduce his ROM to something more appropriate (where he can maintain a natural lordotic curve in his back). We've since changed this in his programming and his squat is coming around nicely.

Using Stiffness For Better Performance

Now I'm sure some of you are thinking something along the lines of, "No! Stiffness sucks! I don't want any of that damn stiffness hibbity-jibbity stuff going on." More than anything, I think it comes from a misunderstanding of the term "stiffness."
People hear the term and they assume that it means being immobile, inflexible, or something along those lines. However, stiffness doesn't have to be bad. If you watch any high-level athlete move, they know how to utilize stiffness to produce more powerful movement.

Way back when, this athlete (so to speak) also used stiffness to produce powerful movements.

In the hips of an elite powerlifter; the stiffness generates starting and reactive strength for big squats and pulls. The posterior of an athlete with a big vertical jump uses stiffness in the gastroc, soleus, and Achilles to produce serious hang-time. It's not so much the stiffness that causes the issue, but the imbalance in stiffness.
In our recent article on Olympic vs. Powerlifting Squats, Geoff Neupert and I discussed the benefits of going deep while squatting. Olympic lifters are usually a great example of balanced stiffness.
You'll see these lifters go ass-to-calves deep in a squat, with no true rounding of the lower back. How? They've balanced the stiffness between their hips and lumbar spine to be able to do so.
The concept of stiffness goes beyond a single article, but this is a good starting point to make you aware of its presence and how it may be influencing your exercise performance.
Bill Hartman and I are currently working on a project that will outline our progressions to not only get you squatting deeper, but to do so with an appropriate lower back posture to boot. Stay tuned for that.

Summary

Understanding human movement isn't the easiest thing in the world. Just when you start to understand the basic concepts like mobility and stability, new influences like stiffness pop up to muddy the waters and cloud our perceptions as to what is "true."
So where does this leave us? The obvious goal in training now becomes not just balancing mobility and stability, but also balancing stiffness between adjacent structures to produce smooth and efficient movement. When we do that, we have the best chance to perform at an extremely high level while minimizing the risk of injury.

About the Author

Mike Robertson, MS, CSCS, USAW, is the President of Robertson Training Systems and the Director of Custom Athletics in Indianapolis, Indiana. Mike received his master's degree in sports biomechanics from the Human Performance Lab at Ball State University.

To learn more about Mike, visit his website and be sure to check out his books at the online store.

References

1: Kibler, WB. (1998) The Role of the Scapula in Athletic Shoulder Function. Am J Sports Med, 26, 325-337.

2: Sahrmann, S. (2002) Diagnosis and Treatment of Movement Impairment Syndromes. St. Louis: Mosby, Inc.

3: McGill, S. (2007). Designing Exercise for the Painful Low Back. Chicago: Perform Better Functional Training Summit.

4: Bogduk, N. (2005). Clinical Anatomy of the Lumbar Spine and Sacrumi. Atlanta: Elsevier Health Sciences.