Joint centration describes the optimal mechanical position of joints and balanced muscle forces around those joints. The term joint centration is used mainly within a physical therapy and sports rehab technique called Dynamic Neuromuscular Stabilization (DNS). This technique has also become very popular with chiropractors interested in educating clients on how to enhance core stability and overall nervous system functioning. Functional joint centration can be very integral to managing musculoskeletal pain.
DNS exercises are interested in promoting a deep level of core stability around neutral joint positions of the spine and educating high-quality, proper movement (motor control) in the hip joint and shoulder joint while maintaining balanced muscle forces (muscle activation).
What is a neutral spine?
Simply put, a neutral spine is midway between spinal flexion and extension. If you're familiar with the basic yoga stretches called cat and cow, we can use these to understand what is meant by neutral spine. In the Cat position, the spine is fully flexed to the point that no more movement can occur in that direction. In the Cow position, the spine is stretched in the opposite direction, into extension. Now consider finding the midway point (neutral position) between those two, often called tabletop.
According to Dynamic Neuromuscular Stabilization (DNS), joint centration is the position in which the spine is most protected and the least susceptible to injury. Also, muscle functioning and body mechanics are thought to be optimal when the spine is aligned correctly in this neutral position.
What does muscle imbalance mean?
With all this talk of joint positioning, it's essential to understand that muscle forces influence the position of joints along the kinetic chain. Ideally, muscles on each side of a joint have similar strength and coordination. If one side is excessively dominant or weak, it's often called a muscle imbalance.
Previously, I mentioned spinal flexion, spinal extension, and neutral position. Muscles in the front of the body, such as the abdominal wall, are usually responsible for spinal flexion. Muscles in the back of the spine, such as the erectors, are used to extend the spine. Joint centration of the spine occurs when there is a balanced activation of the stomach flexors and the back extensor muscles.
Physical therapist Diane Lee has described these tendencies in the easiest of ways to understand. For example, she uses the term back gripper to describe people with weaker stomach muscle control and overuse of low back muscles. This imbalance causes their spine joints to jam into extension. This condition is also sometimes called lower crossed syndrome and anterior pelvic tilt.
In opposite situations, people have weak back muscles and overuse stomach muscles. Diane Lee calls these people chest grippers. However, she also has a term for people who clench their butt muscles as butt grippers. Both posture types usually have a more flat spine and possible posterior pelvic tilt.
Core stability
Before explaining core stability, it's helpful to define the core. The core is essentially the pelvis region. It's the center of gravity and the foundation for movements. Technically, any muscle that attaches to the pelvis is a core muscle. However, the deepest level of muscles for spine stability are the diaphragm, pelvic floor, transversus abdominis, and multifidus. These muscles, also called the intrinsic core, form a canister and pressurize the midsection, providing a rigid core that stabilizes and protects the spine.
The best core stability exercises engage the intrinsic core muscles while resisting movements (aka anti-movement). To understand this, consider the following two exercises. 1. Side bending while holding a weight in one hand. The repetitive side bending creates spine movement and is therefore not a stability exercise. 2. Holding a heavy weight in one hand and then walking. This is called a suitcase carry and is considered an anti-side bending stability exercise.
Application of joint centration
Now that you understand 'neutral spine' and 'core stability,' let's put these concepts together as they relate to joint centration. Within the DNS model, there is an emphasis on helping patients find their neutral spine/joint centration and then engage the core muscles. For example, teaching the back grippers (those whose spine is often more extended) to do a pelvis tuck first. The pelvis tuck is also called an imprint in Pilates and slightly flexes the low back without excessively rounding the rest of the spine.
This idea of joint centration is then applied to other spine regions. Once appropriate body awareness of joint centration is developed, specific core exercises are implemented to strengthen around proper alignment. A key concept within DNS is that a deep level of stabilization is necessary for appropriate joint centration. Meaning that once stabilization is achieved, it can be maintained during motion like functional movements or exercises.
Neuromuscular control
Until now, we've only discussed muscles and joints. However, the brain & spinal cord (nervous system) ultimately controls how muscles move the body (motor control). Improving neuromuscular control is essential to improve joint centration and enhance overall movement pattern.
A lack of strength in core muscles rarely leads to injury. What's more common is that poor coordination and timing of the nervous system are the cause of injuries. If the nervous system has an exaggerated or jerky response, there will be too much muscle force which can cause damage. However, an injury will also occur if the nervous system does not engage appropriate muscles quickly enough. The ultimate goal is balanced synchrony of all fine-tuning stabilizers of the spine during any movement or activity.
We're not supposed to live with a stiff core as if holding a plank all day. What's more important is to be relaxed and to move gracefully, but the ability for the nervous system to engage when needed. It's also important that the nervous system can respond smoothly with the necessary amount of core stabilization when needed.
Neuromuscular control can be trained through techniques such as sensorimotor training. This involves a combination of manual therapies such as acupuncture, chiropractic adjustments, and myofascial release. Next, postural exercises are used to discover proper body awareness. Finally, specific core stability and balance/agility training can be used as a corrective exercise to help optimize the nervous system's function.
