Practical Science on Movement and Pain
Dynamic joint mobility drills are becoming very popular, and are starting to replace static stretching as a way to warm up, train healthy movement patterns, and (p)rehab injuries. Mobility work can be defined as deliberate movement through a defined pathway, done repetitively, usually without resistance. Examples include wall slides or arm swings for the shoulders, clam shells or leg circles for the hips, and cat/cows or rotations for the spine.
Joint mobility drills have several advantages over static stretching. First, they involve movement, which is good, because you probably want to get better at moving, not just staying still with your limbs splayed out. Second, most of the work in a static stretch is done at end ranges of motion that don’t get used very often. By contrast, joint mobility drills usually involve movements through the middle ranges of motion where most of life and sport occur. So they promise to have more applicability to real world tasks. Healthy athletic movement at most joints has far more to do with quality of motion than quantity of motion.
So the trend toward mobility drills is a very positive development. However, I believe that people often fail to obtain the full benefit of mobility exercises, mostly because they do not appreciate the neural mechanisms by which they work. The mainstream idea is that joint mobility drills work by making changes to the local muscular and connective tissues involved in the movement. In my opinion, mobility work has only a limited ability to cause significant adaptations in the mesoderm. Instead, it works by making changes to the virtual representations of those structures in the brain. In other words, mobility work is about function not structure, the brain not the body, the software not the hardware, the ectoderm not the mesoderm, the driver not the car. OK, enough with the metaphorical distinctions. Here’s a detailed explanation what I mean.
Joint mobility drills are a weak stimulus to the mesoderm
There is little reason to believe that joint mobility drills have any notable effects on the local mesodermal tissues that are being mobilized.
Unlike weight training or endurance training, mobility work does not provide enough resistance or energetic demand to cause adaptations in the size or endurance of muscle cells. Unlike stretching, it does not involve enough time at the end ranges of motion to permanently add more muscle or connective tissue length. Unlike sports or other habitual physical activities, it does not create enough mechanical stress to the tendons and ligaments and joint capsules to cause any significant connective tissue remodeling (unless you did thousands of repetitions at a pretty good speed.) Joint mobility drills will provide circulation and warmth to the local tissues and synovial fluids, which is great and totally necessary for health. However, we would expect similar benefits from almost any repetitive motion in the same area.
So why would the specific form of a mobility exercise matter? Why not just move all your joints through all their ranges of motion in any old way? My answer is that mobility exercises work by communicating with the brain, and it will only communicate effectively when it sends the correct signals. Here is a discussion of some neural mechanisms by which mobility drills could improve coordination and reduce pain.
Joint mobility drills improve coordination by clarifying movement maps
Coordination happens in the brain not the body. Some key networks in the brain that sense and coordinate the muscles are called the body maps. The body maps are discrete parts of the brain that are organized in such a way as to represent the different body parts, just as lines on a map represent roads. Each part of the body has a separate area of the brain dedicated to moving and sensing that body part.
Body parts that have greater sensory motor demands have bigger maps. Not surprisingly, the map for the hand is significantly larger than the map for the elbow. Thus, larger and more detailed maps means better coordination. The information necessary to maintain and build the maps is provided by proprioceptive signals from the body. Proprioception occurs when movement or touch stimulates nerve mechanoreceptors, which are located all over the body and primarily in joints.
You can sense the effects of mechanoreception on your maps instantly by doing a simple experiment. Try to imagine or sense the exact shape and position of your ears. Now rub just the left ear for a few seconds and then compare your ability to sense the left ear and the right. You will note that it is much easier to form a clear picture of the left ear. The simple reason is that touching the ear activated its mechanoreceptors, which sent a signal to the brain, which excited the neurons in the map for that area. Of course, the additional clarity in the map is only temporary, and after a minute your ears will feel the same.
In order to make long term changes in the maps, you need to place demands on them consistently over a long period of time. When a certain movement is used repeatedly in a coordinated and mindful fashion, there are actual physical and observable changes in the part of the brain that controls that movement. For example, the finger maps in a braille reader’s brain are observably larger than the counterpart of the average person.2
While movement will clarify maps, lack of movement will tend to blur them. In a famous experiment, researchers found that sewing a monkey’s fingers together for a few weeks caused its brain to map the fingers as one unit, not as two separate parts capable of individual movements.3 We would expect similar map blurring to occur when any joint movement is neglected for a certain period of time. This loss of control over previously accessible movements is the neural version of the “use it or lose it” principle, and is sometimes called sensory motor amnesia.
A common area for sensory motor amnesia is the thoracic vertebrae. Most people probably have one or two vertebrae in their upper back that haven’t moved in a certain direction with respect to its neighbor in years. The movement isn’t physically impossible, it’s just not part of the brain’s current movement programs due to neglect. A good analogy might be a language that you could once speak fluently that you haven’t spoken for years. The knowledge is in there somewhere, but a good portion of it is not readily accessible without some brushing up.
The right mobility drill would be structured to require the brain to brush up on its thoracic movement skills and reactivate some rusty movement programs. If the brain remembers how to move a currently static vertebra, the result is an immediate qualitative change in the movement of the entire spine. The decisive change is not to the physical tissues of the vertebral joint, but to the way that the brain maps the vertebrae for sensation and movement.
Blurred body maps can create pain
Accurate maps also have important consequences for how we feel. Phantom limb pain is a dramatic example. Many people with an amputated limb experience pain in the missing body part. This is because even though the arm is gone, the virtual arm in the brain lives on, and can be stimulated by cross talk from nearby neural activity. When this occurs, the brain creates a sensation of the missing arm that is incredibly realistic and often excruciatingly painful.
Some pain researchers believe that less severe instances of mapping errors may be involved in many chronic pain conditions. Numerous studies have shown that sensory motor illusions caused by mirrors or other tricks can cause pain. For example, if you immerse your index and ring fingers in warm water and the middle finger in cold water, this will often cause your middle finger to feel painfully hot. Other studies have shown that pain from these illusions can be alleviated with proprioceptive input that corrects distortions in the maps.4 For example, an amazing treatment for phantom limb pain involves placing the remaining limb in a mirror box in such a way that it fools the brain into thinking the missing limb is alive and well! Based on these and other studies, many pain researchers believe that clarifying the maps is a promising treatment for many forms of chronic pain.5
Movement creates sensory gating
Mobility drills can also reduce pain by sensory gating. Sensory gating means that the processing and perception of sense information is reduced by the presence of competing sense information. If your nervous system is busy trying to process signals resulting from movement or touching, it has less ability process signals caused by tissue damage (nociception). Most people will instinctively take advantage of sensory gating by rubbing an area that has just been injured. The rubbing sends sensory signals to the brain which compete with the damage signals. If you feel temporarily better after a massage, exercise, or yoga, sensory gating is probably a major reason why.
Conclusion: How to maximize the benefit of joint mobility exercises
Based on the foregoing, there is good reason to believe that the brain should be the primary target for joint mobility work. With this in mind, here is a quick list of rules to keep in mind when doing mobility work.
1. Avoid pain and threat
If you create pain while doing joint mobility drills, the brain will attend to the pain and ignore the potentially interesting proprioceptive information. Further, the brain is not interested in adopting a new movement pattern that is threatening. Make sure the movement does not cause too much discomfort or create other signs of threat such as holding the breath, grimacing, collapsing your posture, or using unnecessary tension.
2. Be mindful and attentive to what you are doing
Attention enables neuroplasticity, which is the goal. The brain receives massive amounts of sensory information each second and will ignore any inputs it deems irrelevant, uninteresting or redundant. If you pay careful attention to what you are doing during mobility drills, the brain will place a higher value on the resulting proprioceptive information and be far more likely to make changes to your movement maps.
3. Use novel movements
The brain is more likely to pay attention to a stimulus that is novel. Most joint mobility drills incorporate novelty already and that is why they work. However, endlessly repeating the same drill will have diminishing returns. So you might want to change things up from time to time to keep the brain interested.
4. Easy does it
The benefits of moving slowly and gently to improve coordination have been recognized by martial artists, elite athletes and musicians for a long time. The scientific explanation for why slow and easy works requires a post of its own, but here is a start. Slow and easy movement works because it: is inherently non threatening; is less likely to cause pain; allows you to find movement angles that would be missed at higher speeds; improves the proprioceptive signal to noise ratio; allows greater opportunity to focus on the subtle differences in joint movements; and, under the Weber Fechner rule, less force equals greater ability to discriminate in the amount of force used.6
5. Be curious, exploratory and playful
Motor learning is greatly facilitated by a curious playful attitude. All animals engage in the most play during the times of their lives when the educational demands are the highest. This means that play is the best solution to difficult education problems that evolution has found. With this in mind, use mobility work as a way to experiment with subtle variations of how to move and figure out which ones work best.
Next time you do some joint mobility drills, move slowly and carefully, completely avoiding any discomfort. Reduce speed and range of motion as necessary. Use the minimum amount of force and effort to get the job done. Pay careful attention to exactly what you are doing and play with subtle variations to assess which are most efficient and comfortable. Try a few repetitions at the slowest speed you can possibly move. Then see how you are moving. I think you will see some improvements. Good luck!