Mobility and Stability
I bet the majority of us have spent a little time on a foam roller or have used bands to stretch before class. At the very least, the warm-ups used in class incorporate mobility exercises for the shoulders, hips, and any other joints being emphasized that day. Since we’re all on our journey to becoming supple leopards (Kelley Starrett’s term of course), I thought I’d touch briefly on how I approach mobility – as well as its cousin – stability.

Mobility and stability are distinct topics, but very much related and equally important with regard to proper movement. First, what is mobility? A simple way to define it is being able to move a joint (such as the elbow, knee, etc.) through a range of motion, as in descending into the bottom of a squat. Stability, on the other hand, is the ability to prevent or control joint movement when it’s not needed. Some joints are meant to be mobile, and others only stable.
The model that not only helps me remember whether a joint is supposed to be mobile or stable, but also showed me how the body fits together, is the joint-by-joint approach designed by Gray Cook. This model is incredibly straightforward, and really breaks down a complex system into its simplest parts. The joint-by-joint approach is illustrated below:

The first thing to notice is that the joints alternate between mobility and stability. The ankle needs mobility, the knee needs stability, and we continue on up the chain in this pattern.
For ease of reference, the full list of the joints and their movement needs is below:
Foot – stable
Ankle – mobile
Knee – stable
Hip – mobile
Low back – stable
Mid back – mobile
Neck – stable
Shoulder blade – stable
Shoulder joint – mobile
Elbow – stable
Wrist – mobile
Hand – stable
Besides being pretty fascinating, how does this relate to CrossFit? Adhering to these “rules” of stability and mobility will help prevent injuries as well as increase performance. Let’s treat some back squat errors.  
Do your knees cave in? Ensure you have full ankle mobility, hip mobility, and foot stability. A problem could be caused by a dysfunction of any or all of these. Nobody wants to tear an ACL, and I guarantee that fixing the valgus knee collapse will also lead to a bigger back squat!
Torso collapse? Check ankle mobility, hip mobility, and mid-back mobility.
Trouble keeping a neutral spine? (aka “butt wink”) Mobility of the ankles, hips, and mid-back still apply, but consider adding some lower-back strengthening exercises to ensure proper lumbar stability is achieved.
This is just a brief example of how mobility and stability work together in the human body. If you ensure that each joint is doing what it’s made to do, you’re on the way to better movement, less injuries, and more PRs.