15.3 Core Stabilization and Lumbar Motor Control

Core Stabilization and Lumbar Motor Control

Spinal stability depends on the interaction of passive tissue restraint, muscle force and neural control as posture and load change. In rehabilitation, use this model to understand the demands of a task and choose an exercise the patient can practice and progress.

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Manohar Panjabi's Spinal Stability Model

Panjabi proposed three interdependent subsystems in 1992. A change in one subsystem can alter what is required of the others. The response can include compensation, such as increased muscle activity when the task becomes more demanding.

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• Passive: Vertebrae, facets, capsules, discs and ligaments contribute mechanical restraint. Passive resistance generally rises as movement approaches the limits of the available range.
• Active: Muscles generate force and stiffness. Together with their tendons, they help manage forces acting on the spine during motion or static loading.
• Neural control: The nervous system uses sensory input and anticipated demands to adjust muscle recruitment. A change in activation can occur before a predictable load or after an unexpected disturbance.

The Neutral Zone Concept

The neutral zone is the low-resistance portion of intervertebral motion around the neutral position. Passive resistance increases in the elastic zone as motion approaches the physiological limit. In laboratory studies and biomechanical models, a wider neutral zone can indicate reduced passive restraint. Panjabi proposed that it could help explain spinal instability and that other subsystems can compensate. A painful catch in active trunk motion cannot measure the neutral zone or establish a structural instability diagnosis.

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Local and Global Muscle Contributions

Bergmark distinguished muscles acting directly on lumbar segments from longer muscle groups that transfer forces between the thorax and pelvis. Use the distinction to reason about a task. The contributions change with posture, external load and the line of pull.

The abdominal wall, diaphragm and pelvic floor can influence intra-abdominal pressure. Experimental increases in abdominal pressure can increase lumbar stiffness. The forces on a particular disc also depend on position, the external load and the muscle activity used to produce that pressure. For example, a heavier carry can increase the trunk moment and recruit more muscle force even when the back moves very little.

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Motor Control Findings in Low Back Pain

• Anticipatory activation: Hodges and Richardson measured trunk muscle activity during rapid arm movements. Their low back pain group showed later transversus abdominis onset than controls in that task. This is a group difference in timing under specified test conditions.
• Multifidus size: Hides and colleagues studied patients with acute, first-episode unilateral low back pain and a localized multifidus size difference. In their comparison, the difference persisted despite pain improvement in the group that did not receive specific exercises. A change in pain or function and a change in muscle size are separate outcomes.

These findings help explain why a patient might practice coordinating trunk and limb movement. Use the patient's actual movement difficulty and goals to select the task and monitor response.

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Motor Control Rehabilitation Progression

The 2021 APTA low back pain guideline supports movement-control and specific trunk muscle exercise for chronic low back pain with movement-control impairment. The patient can start at the task level that matches their symptoms and ability.

Pressure feedback can help a patient notice movement. For the Enovis Stabilizer, supine draw-in training uses the cell under the lumbar spine at a 40 mmHg baseline and aims to hold it steady. Its separate prone procedure puts the cell under the abdomen at 70 mmHg and looks for a 6–10 mmHg decrease. The gauge reports external cell pressure and cannot establish isolated transversus abdominis recruitment.

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Stuart McGill's Three Trunk Exercises

Axler and McGill estimated different lumbar loads across abdominal exercises. Those estimates compare the tested tasks. The NIOSH 3.4 kN criterion was used in designing an occupational lifting assessment and does not establish a disc injury threshold for exercise. The modified curl-up, side bridge and bird-dog offer ways to train trunk control or endurance with limited lumbar movement, adjusted for symptoms and goals.

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1. The Modified Curl-Up

• Biomechanical Goal: Challenges the abdominal wall while limiting lumbar movement.
• Technique: Patient lies supine with one knee bent and one leg extended flat on the floor. Support the comfortable lumbar curve with the hands. Lift the head and shoulders slightly while limiting lumbar movement and breathing normally. Select a hold and repetition count that the patient can repeat with control.

2. The Side Bridge (Side Plank)

• Biomechanical Goal: Challenges the lateral trunk muscles to hold the trunk against gravity. Support from the knees or feet changes the demand.
• Technique: Use side support on the forearm and bent knees or the feet. Raise the pelvis and keep the trunk aligned over the chosen base of support. Increase the lever arm or hold time as tolerated.

3. The Bird-Dog (Quadruped Contralateral Reach)

• Biomechanical Goal: Challenges trunk control during limb movement. A single arm or leg reach can precede a simultaneous contralateral reach.
• Technique: Begin on hands and knees. Slide or reach one limb before trying a simultaneous opposite arm and leg reach. Reduce the reach if the person needs to turn or arch the trunk to maintain balance.

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The Preliminary Hicks Stabilization Rule

Hicks and colleagues followed 54 people with nonradicular low back pain who all received eight weeks of stabilization exercise. Their study defined success as a reduction of at least 50% in the modified Oswestry Disability Questionnaire score. Four baseline findings contributed to their preliminary model.

The derivation reported a positive likelihood ratio of 4.0 (95% CI 1.6–10.0) for at least three findings. Using the derivation cohort's 18/54 success rate gives pretest odds of 1:2. Multiplying by 4 gives post-test odds of 2:1, or about 67%, within that study. This was an outcome association among treated participants. A later randomized comparison did not validate the four-item rule as a way to select patients for stabilization exercise. Use task performance and reassessment to guide an exercise trial.

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Clinical Case Scenario

A 32-year-old female dental hygienist presents with a 6-month history of intermittent, non-radicular low back pain that began following the birth of her second child. She experiences sharp catches of pain when returning to an upright posture after bending over to treat patients. On physical examination, active trunk flexion reveals an obvious painful arc in mid-range and an instability catch accompanied by a positive Gower sign (she places her hands on her thighs to push herself upright). Her passive straight leg raise is 96° on the right and 98° on the left (average 97°). Segmental passive accessory intervertebral motion (PAIVM) reveals tenderness over the L4–L5 spinous process; during the Prone Instability Test, her familiar resting PA tenderness is completely abolished when she lifts her feet off the floor.

• Clinical reasoning: The four preliminary findings are present. Their main value here is describing how pain changes with trunk movement and muscle effort. Screen for other causes and use the work task to test what the patient can change and tolerate.
• Physical therapy plan: Practice a supported reach and adjust stool height or forearm support for the work task. Trial a tolerable trunk exercise such as a shortened quadruped reach and build the reach or duration gradually. Recheck pain and tolerance for a comparable period of simulated dental work.