2x4s, balance, and hip mobility


Five years ago, while I was training for my MovNat level I certification, I purchased an 8 foot long 2x4 to practice the balance skills of walking forwards, backwards, and sideways. Sideways was challenging for me, so I set it up in my living room and practiced every time I walked through the house. (Side note: our house at the time was tiny, and our living was literally open space so we could move around on the floor. The 2x4 was the only piece of “furniture” I had).

Walking on the 2x4 intuitively made sense, and clients found it to be a fun challenge. I noticed foot and hip mobility were often better after a few passes, which I found interesting, but I wasn’t quite ready to dive into the potential aspects of why.

Five years have passed and I have read and thought a lot about the feet and gait mechanics. I have a few theories about what happens when you walk across a 2x4 and what might be happening, but first, let’s look at how the foot responds to the ground during regular walking.

When you take a step, a foot stays in contact with the ground while your body passes over it. There are a few things that happen when the foot absorbs the impact from the ground and transmits load up the leg before it propels the leg forward. Think about it for a second- your foot is responding to the ground. Would it make more sense for the foot to stay stiff or for it soften a bit?

Soften, right? Otherwise, it’s like hitting a steel beam with a rigid arm- it doesn’t feel very good or result in an elastic response.. 

The technical term for the absorption phase of the foot is pronation. The technical phrase for the stiffening phase of the foot that happens to propel the foot forward is supination. Before we get too bogged down with technicalities, let’s focus on the pronation phase and what else needs to happen for all of the joints to play happily together.

Walking is a series of rotations that results in a forward looking trajectory. From the ground up, rotation occurs as the arch comes closer to the ground, pronating to attenuate the force of the ground. The ankle responds a little bit as well; the inner edge of the heel comes just a little bit closer to the ground, moving into eversion.

The next bone in the chain is the tibia, the shin bone in the front of the leg. If the arch is coming closer to the ground, what way is the tibia moving? Is it rotating in or out?

If you guessed (or logically processed), that the tibia rotates inward, you are correct. The tibia responds to the movement at the foot by internally rotating.

Above the knee joint (which responds like the ankle by moving slightly inward during the stance phase, a fancy way of saying the stage of walking when the foot is on the ground), is the femur, the long thigh bone. If everything below the femur is moving in, how would the femur respond to best absorb the load?

Yes! You are right- it would move inward, internally rotating. The pelvis internally rotates as well, allowing the foot to pull the pelvis over it.

The whole situation reverses to propel the leg forward and push the foot off of the ground- the foot becomes rigid and the arch moves away from the floor, the ankle inverts just a little bit, the tibia externally rotates, the femur externally rotates, and the pelvis externally rotates. It’s like a chain- one thing moves, affecting the next above (or below) it until at some point, the whole system reverses. If the goal was to define neutral, it would be the point where everything is balanced- right before the foot moved from stance to propulsion. 

Another way to think of it is pushing is associated with externally rotating and pulling is associated with internally rotating. When the foot lands, it’s pulling the pelvis over it, and at just the right moment, the foot pushes off of the ground. 

You can feel this entire situation in a squat, if you think about pulling yourself down- you will notice an internal movement of your tibia and femur. When you decide to push the floor away from you and return to an upright position, there is a shift and the bones move into external rotation.

So what about the balance beam? Why does this improve balance and general mobility in the hip for some people?

Imagine you do the pushing off aspect of walking really well. Your foot supinates, your tibia externally rotates, and your femur externally rotates, but when the foot lands to absorb forces, the bones don’t change position very much and internal rotation is limited. What would that do to your balance and basic mobility in the hip joint?

If the foot has a tendency to be rigid, you are going to spend a lot of time using the outside of the foot and not very much time using the arch area, the center of the heel, or the big toe side of the of the ball of the foot. That’s a lot of surface area that you aren’t using when you balance and that’s a lot of information you aren’t receiving from the pressure of the foot against the ground- there are mechanoreceptors that respond to change in position and pressure in the bottom of the feet. Those mechanoreceptors let the brain know where the body is located in space and help inform which options are available for movement. If they don’t detect a change in position or pressure, they have no information for the nervous system- a bit of a conundrum when it comes to motor planning and execution, and a problem when it comes to balance.

If the foot is rigid and the femur responds to the position of the foot by remaining mostly in external rotation, how would that feel in the hip joint? Imagine you sat on the ground, knees out to the side and feet crossed at the ankles for three hours and then tried to sit in a chair with your knees touching and your feet moving away from each other. How would that feel?

Probably not great and you would more than likely experience a sensation of stiffness. So if, day and day out, your femur remained mostly in one position, it probably would feel a bit stiff when you tried to move it in a different way.

Okay, so what does a 2x4, possibly the world’s least expensive piece of fitness equipment, have to do with all of this?

Now is a good time to do a (brief) review of basic motor control terms. When you go to perform any physical task, there are an infinite number of ways the task can be done. The amount of options you have at any given joint is the degrees of freedom available at the joint to perform the task. Think about the act of walking: you could walk with your knees high or your knees low. You could walk with your feet wide or narrow. You could walk with your feet landing in front of your or behind you. You could walk with your knees really straight or with your knees really bent. You get the idea. 

What’s interesting is that even with all of these options available, you probably walk in a very consistent way. Movement is funny like that- unless you practice doing things differently, your neuromuscular system decides which way it prefers to do things based on past experiences and sticks to it, even if there are more efficient ways to do the same task.

A constraint reduces the amount of options you have to perform a task- it lessens the degrees of freedom available. Task constraints can be used to introduce a different way of doing a well established skill or improve coordination.

A 2x4 introduces a constraint to the activity of walking. If your habit is to avoid internal rotation, it’s going to be difficult to balance on the 2x4. 

Why? The nature of being slightly off the ground on a surface that requires walking with one foot exactly in front of the other and having a board that dictates your feet point (mostly) straight ahead means that if your tendency is to spend the majority of your time on the outside of the foot without moving into pronation, you won’t have good contact with the 2x4 when you transition from the back foot to the forward foot. The lack of stability you experience means you will try and figure out a way to stay stable, This can include less efficient strategies such as clenching your jaw, holding your breath, and tightening your fists. If your coach (or the voice inside your head that is serving as your coach), notices you are doing these things and asks you not to, you will figure out how to get across the board another way. If you are moving slowly and given repeated exposure to the task, your foot (or feet, depending upon the situation), will do this by moving into pronation. Assuming your lower limb functions in a coordinated fashion, the other parts will follow. 

Since walking across the 2x4 is dynamic, once the nervous system realizes it’s safe, it’s a way to repeatedly expose yourself to a position you aren’t used to being in and since that position is a natural part of an efficient gait cycle, there tends to be a transference of neuromuscular coordination. Your balance will improve, your hips will feel less tight because they have more options, and things will feel a little more coordinated, all because you walked in a constrained way. Kind of interesting, isn’t it?

Obviously, this won’t be the case for everyone, because not everyone has a habit of avoiding pronation and internal rotation, but for those it does help, it’s a pretty simple exercise to implement.

The other way I use a 2x4 for working on gait mechanics is to teach big toe loading during plantar flexion. Plantar flexion is a movement that is synergistic with supination (meaning they often occur together during coordinated movements). Remember how I mentioned supination goes with tibial external rotation during gait? It also goes with big toe dorsiflexion- the big toe bends up when you toe off. Except when it doesn’t because you are avoiding placing load in that area, a common occurrence in a society that often neglects toe and foot health. If you don’t load the big toe during gait, your foot travels less smoothly through the area. 

Think about it. The big toe has more surface area to push off of than the other toes. If you aren’t pushing off of the big toe, the neuromuscular system gets creative to propel the foot forward. Creativity doesn’t always equal efficiency.

Back to the 2x4. If you stand so the 2x4 is horizontally in front of you and you place the toes/ball of the feet on to the 2x4, you have a constraint that orients your toes straight ahead. If you lift your heels off of the ground so they are above the balls of the feet, if the weight moves into the little toe side of the foot, you won’t feel secure. The nervous system prefers feeling safe, so if you have the mobility, your neuromuscular system will change your strategy so the load is on the big toe side of the foot. If you start to move sideways, every time the weight moves to the outer edge of the foot, you will feel unbalanced. As a result, there will be a continual correction towards the big toe side of the foot, teaching efficient loading of the big toe.

Aside from the mechanics of what is going on, balance work is fun. People enjoy it and when they struggle, they become curious, trying over and over again until they succeed. Introducing variability, challenge, and novelty into anyone’s program is a good thing. Using simple tools and understanding how to use constraints can provide an element of play and have a profound impact on someone’s movement.

Part II will discuss how balance training can decrease anxiety, a subject I’ve written about before, but focusing more on the practical application.

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