Developmental Movements: Part Two

In the previous post I pointed out that the developmental movement patterns learned in infancy are building blocks for the more complex movements that we use in our daily lives as adults. These simple patterns are combined to form sophisticated movements, just as words and letters are combined to make sentences. One implication of this combinatorial system is that any compromise to one of the foundational building blocks will cause the entire structure built on top to suffer. For example, if you are limited in performing a basic movement like squatting or rotating, there are a very wide range of everyday movements that will be compromised. With that in mind, it is interesting to look at the context in which these developmental patterns emerged, and ask whether that context can help adults recover or improve primitive patterns that may be neglected or in a state of disrepair.

One important aspect of the developmental environment is position. Primitive movement patterns are learned in developmental positions - supine, prone, quadruped and tripod positions, oblique sitting, kneeling, half kneeling, squatting, etc. These positions offer several potential advantages to an infant trying to learn useful developmental patterns. And, more importantly, to an adult trying to recover or brush up on such patterns. In fact, it is interesting to consider that developmental positions are used extensively in almost any form of rehabilatative movement or sensory input, such as massage, physical therapy, corrective exercise, yoga or pilates. Here's why.

Reduction of stability and balance demands

First, developmental postures drastically reduce stability demands compared to standing postures. On the ground, there are simply less moving parts and therefore fewer variables to control at the same time. In standing, postural balance requires coordinated activity of the ankles, knees, hips and spine etc. In a kneeling position, the ankles and feet are taken out of the equation, which simplifies the motor control required for erect posture. Further, the center of gravity is lowered closer to the base of support, which increases stability.

Stabilization demands are reduced to almost zero in the supine position. Thus, there is greatly reduced perception of threat related to falling, as well as any undesirable protective mechanisms related to that perception, such as stiffness, weakness, discomfort and altered motor programs. Although most of us are not consciously afraid of falling as we walk or squat, there is always a significant degree of unconscious nervous system activity devoted to preventing such an occurrence. This may involve excess protective muscle activity and restriction of uncontrolled mobility. To the extent that a developmental position can reduce this protective activity, it can facilitate the recovery of motor patterns that are much harder to find in standing positions. For example, one may find it easier to obtain full flexion of the hip required for squatting, because the hip musculature is not occupied with stability or balance demands. 

Increased proprioception

Another advantage of developmental positions is that they increase proprioceptive feedback through contact with the floor. For example, it is easier to perceive the shape and movement of the spinal curves and ribs while lying on the floor than standing in space. In supine, you can sense lumbar flexion by feeling the low back press into the floor. In standing, this form of feedback is not available.

Increased constraints

Here is the interesting part. Part of the reason developmental positions improve movement is by limiting movement options. Getting on the floor constrains degrees of freedom in a way that reduces the number of motor patterns that can be used to perform a particular task. Thus, many potential “bad” patterns of movement are unavailable, while all the “good” ones remain. (If developmental positions precluded the use of fundamental movement patterns, they never would’ve developed in the first place!) Developmental patterns are easier to find when they are one of very few potential solutions to a motor challenge.

For example, in crawling, there are fewer choices of how to use the arms than in walking, because one arm must always help support the body weight. Because the hand is fixed to the ground, the arm muscles move the body relative to the arm, instead of the arm relative to the body. The supporting arm will synchronize with the opposite side supporting leg, so that a cross lateral pattern of limb movement emerges.

In walking, this same cross lateral pattern should be preserved. But because the arms have additional degrees of freedom, it is no longer required. The arms don’t need to bear weight, so they are free to move out of sync with the opposite side leg. And the muscles on the leading arm are no longer required to “pull” the body forward as in crawling - instead they can operate more to pull the hand back. To feel how walking can preserve the “closed chain feel" of the arms in crawling, imagine that you are walking with ski poles. The hand that reaches forward, like the crawling arm, to some extent becomes a “fixed point” in space from which the muscles connecting the arm and the trunk can pull the body forward. If you walk this way, you may feel an increased sense of integration of the arms with the trunk during gait.

So walking presents an opportunity to neglect a primal locomotion pattern that is more compulsory in crawling. If this neglect eventually results in some sensorimotor amnesia with respect to this pattern, perhaps crawling can help reactivate it. This is because crawling eliminates the possibility of using many specific and complex patterns of movement, while preserving only the simple fundamental options.

Here’s another example. If I am a baby lying flat on my back, and I want to reach an object that is a hanging from a string a few feet in front of my sternum, there are very few combinations of joint movement and associated muscle activation patterns that will get the job done. Any solution will almost certainly involve: shoulder flexion to ninety degrees; scapular protraction; and rotation of the rib cage to the opposite side of the reaching arm. The synergy between shoulder flexion, scapular protraction and thoracic rotation is a very basic reaching pattern that can be used as a building block in many other contexts, including throwing, striking, pushing, running, walking, etc.

Now consider my reaching options in sitting, where I have more degrees of freedom. Let’s say I am reaching for a computer mouse that is a few feet in front of my sternum on a table. I could use the exact same muscle synergy I did while on my back, but I have many other options as well. Many of these will be very specific and idiosyncratic, useless in all but very limited contexts. For example, I could reach the mouse without shoulder flexion, scapula protraction or even thoracic rotation, by flexing the elbow and bending forward from the hips. Or I could stand up, turn around and reach backwards to get the mouse. With more options, there are more “wrong” answers. The primal pattern is not compulsory – there are motor solutions that are entirely specific to the context, and useless elsewhere.

By contrast, in the supine position, the optimal reaching synergy, which forms a great building block for other movements, is really the only way to get the job done. The tendency for this position to elicit a proper reaching pattern is part of the reason the Turkish get up is a popular corrective exercise.

We could think of several other examples. While sitting on the floor, looking behind us requires a cooperative and integrated rotation from the neck, scapula, thorax, low back and hips. In standing, we can avoid movement in the thoracic spine and/or the hips by using compensatory movements at the knees, ankles and feet. In prone, if we want to see the world, the thoracic spine needs significant mobility into extension and rotation, and the scapula and neck must coordinate their activity. In standing, we can see above us quite easily without much work in the thorax, again by using compensatory motions in the ankles or knees.

In each case, the additional degrees of freedom available in standing make it possible to neglect primal patterns that are more compulsory in developmental positions. The result is use of an idiosyncratic and specific pattern that might get the job done, but is less efficient, distributes the stress of movement in a non-proportional way, and misses an opportunity to maintain a very important building block for healthy movement.

Thus, returning to developmental positions is a way to encourage the use of primal patterns that may be getting ignored in everyday life. It's not a magic bullet of course, or the only way to improve movement, but it is a potentially useful tool. And it's why many people get down to the ground when they want start moving better and feeling better.

In the next post, I’ll discus how adding resistance to a movement can also create constraints that encourage the use of developmental movement patterns.