I just got home from a week in Oslo, Norway, speaking at the AFPT Convention for personal trainers. It was an awesome event, and I was able to stand shoulder to shoulder with some amazing presenters, including Bret Contreras, Alan Aragon, James Krieger, Brad Schoenfeld, Jacob Wilson, Nick Tuminiello and a bunch of other world-class individuals.

My talk was on assessments, and I walked away feeling very good about how the information was received. One question I got after the fact was how do you know that a factor in movement restriction is stability, when it’s something that can’t easily be measured or determined where the source of that stability is coming from, and it got me thinking.

In many ways, we can easily measure mobility. We take a goniometer, which is a fancy protractor used to measure joint angles, and see how far you can push a joint through a range, or you have the person actively move that joint through a range and measure it via active means.

Stability is a little bit of a different concept. It could come down to how the word is being used in the fitness industry, but depending on who you talk to it could mean anything from relative strength of the joint to movement-resistance qualities, to general stiffness or even reactive capability to lock a joint down during impact activities.

Classically, there’s a couple different definitions of stability:

1. the quality of being stable

2. (Aeronautics) the ability of an aircraft to resume its original flight path after inadvertentdisplacement

3. (Physical Geography) meteorol

4. (Biology) ecology the ability of an ecosystem to resist change

5. (Electrical Engineering) electrical engineering the ability of an electrical circuit to cope withchanges in the operational conditions

Essentially, in each concept the underlying meaning seems to come down to resistance to change inputs. I push on your shoulder, and you try to not fall over. If you fall, you’re not very stable. The concept of a pyramid sitting on it’s base or sitting on it’s point works well to demonstrate this. The base is a more stable resting place than the point.

 

By this concept, the less a system moves the more stable it is. There’s a tradeoff here, as in the human body the less a joint can move the lower its force or power output can be. Joints like the shoulder or hip are caught in the middle of a tradeoff between being highly mobile and powerful while being inherrently unstable, which means in order to produce power there has to be some degree of control over that mobility.

Because of this tradeoff, it’s difficult to potentially measure stability as we can with mobility. It’s dependent on a bunch of factors, such as relative position, direction and magnitude of external force, and anatomical considerations to name a few. It’s also a challenge to measure the relative stability of a system and it’s ability to not move or be deformed without finding the breaking point of that system, which is hard to justify to paying clients why you just wrecked their spine.

In keeping with the definition of stability being resistant to change, any stability exercise would have to involve a resitance to disturbance from an outside force, and would likely involve minimal or no movement. An isometric would be a good example of this, however the downside to this concept is that a body in motion is rarely not in motion, so a non-moving test wouldn’t necessarily translate well to a moving body.

Think of a sprinter and how their body is constantly moving through a range of motion, but they have to buffer ground impact forces on each step down the track. For the moment their foot is in contact with the ground, they have to be stable enough to handle their foot pushing into the ground and the ground pushing back through their foot in order to accelerate down the track, but for the rest of the time that they’re airborn, they have a very high mobility that doesn’t have any input from the ground to require them to be stable, until their stride direction changes from one step to the next and their muscles pull to produce force and direction change.

Can we actually measure the stability of a joint through something like this? I don’t know. We can do things like video motion capture using dots on joints to determine motion between segments, but these are placed on the skin and somewhat in accurate in terms of what is happening deeper than superficial at the level of the joint and its’ mechanics.

We can manually palpate the joint and see how far we can glide it during passive and isometric conditions, but this becomes a lot harder to do in moving segments. I don’t know too many people who are able to palpate the motion of an SI joint reliably, let alone during a full sprint to button hook pattern in a football player in real time.

So if we can’t measure stability accurately, can we actually posit that it’s what affects movement, pain, or dysfunction at the level that it is commonly considered to affect how we move or don’t move? Is it as simple as saying “do this exercise to improve your stability” when we can’t actually measure whether the person is more or less stable after doing that exercise, or even to measure the stability of the system at all?

Additional to these questions, if we do an exercise and some outcome changes, such as hip range of motion, can we assume that the change was due to an improvement in stability somewhere in the body, or is it due to other neural or mechanical issues? This directly affects my thought process in how doing a core or breathing drill can alter hip internal or external range of motion that I’ve presented previously, so I no doubt have to alter how I theorize the involvement of stability with mobility.

At the end of the day, these are all just big idea questions that I currently have no answers for. I’m sure there are people out there who are smarter than I am who have thought of these things before and have come up with answers, and I hope to understand them