Core Stability

Original Editor - Sem Bras

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Definition

For proper movement and to perform a wide spectrum of functions and activities "stability" is required, it is provided in a co-ordinated manner by the active structures (eg muscles), passive structures (eg lumbar spine), and control by neurological systems.

The core is the centre of our body and it functions to stabilize the trunk while the arms and legs move during functional movements. When we view it this way, we see that the core actually includes:

1. Muscles that stabilize the hips.
2. The system of muscles that make up the torso (on the front, the sides, and the back of the body).
3. Muscles that stabilize the shoulders.
4. abdominal drawing in maneuver (Figure 1) to sit ups or “plank” type exercises (Figure 2).

The core muscles importance relate to the cores functions ie to spare the spine from excessive load and transfer force from the lower body to the upper body and vice versa. Having a strong, stable core helps us to prevent injuries and allows us to perform at our best. In order to protect the back, ideally we want to create 360 degrees of stiffness around the spine as we move, run, jump, throw, lift objects and transfer force throughout our body. We do this when all of the muscles in our hips, torso and shoulders work together

Clinically relevant anatomy

The core is a box structure made up of the abdominal muscles in the front and the sides, the paraspinal and gluteal muscles at the back, the diaphragm at the roof, and the pelvic floor and the hip girdle muscles as the floor. The abdominal muscles create a rigid cylinder around the spine during movement and provide stability. The activity of the transverse abdominis is recorded during the entire range of flexion and extension of the spine. This co-activation of the abdominal muscles during spinal movement is necessary to maintain spinal stability.

The pelvic floor muscles also form part of the core. The increased effort by the abdominal muscles can only increase intra-abdominal pressure during spinal movement if there is co-contraction of the pelvic floor musculature.

The muscles in the back of the core or that which envelope the vertebrae can be subdivided into

1. The deeper uni-segmental muscles, i.e., the multifidus. The multifidus, which is deeper, has direct attachments to the spinal segments, and allows stabilization of the motion segment during lifting and rotational movements of the spine. The deeper uni segment muscles being close to the axis of the spine act as force transducers. Higher concentrations of muscle spindles are located in the smaller uni-segmental muscles
2. The larger multisegmental muscles like the erector spinae are involved in lifting, and the oblique abdominal muscles are involved in rotational movements of the spine. These larger muscles do not have a direct attachment to the spinal segment and hence are unable to stabilize the individual segments.

The neural subsystem anticipates the loading of the spine and activates contraction of the transverse abdominis and multifidus muscle ahead of the loading. When there is a delay in the contraction of the multifidus, the larger and global superficial muscles eg erector spinae contract to compensate for the delay in increasing the stiffness of the lumbar spine (unfortunately, the activation of the large global muscles creates abnormal forces across the individual segments resulting in back pain). There is strong evidence supporting the effectiveness of treatment aimed at normalizing this function by way of specific motor control training, and specific muscle activation.

Local/ deep muscles: muscles that contribute to joint stability and located more centrally near the joint anatomically attaches to many parts of passive elements of the joint to provide stability for the joint during movement.

The local/deep muscles have their origin or insertion on the lumbar vertebra therefore can exert a segmental stabilizing/stiffening effect. Local muscles are;  

Transversus abdominis

Multifidus

Diaphragm

Pelvic floor muscles.

Internal obliques

The mechanism of the deep muscles stability is controversial but transversus abdominis may act like a canister with the diaphragm and pelvic floor muscles. This co-contraction increases the intra-abdominal pressure, which creates an extension moment at the spine and has been hypothesized that increasing stability/stiffness in particular via connections with the thoracolumbar fascia. The multifidus may increase the rotational segmental stability in the sagittal and horizontal plan.

Normal function of the deep muscle system is impaired with back pain. There is strong evidence supporting the effectiveness of treatment aimed at normalizing this function by way of specific motor control training, and specific muscle activation.

Global muscles

There are a wide range of superficial/global muscles that are large, cross multiple segments, responsible for movement. attach the pelvis trunk to the thoracic or upper limb and lower limb and do not attach directly to the vertebrae for example;

Rectus abdominis

External obliques

Parts of the erector spinae.

These muscles generate torque, acting like guy ropes to control spinal orientation and work in co-contraction to control spinal motion in the application of external loads.

Change in Motor Patterns due to Pain

Change in recruitment pattern of core musculature occurs due to injury and pain. Core muscles contract preemptively by feedback mechanism to protect the spine from upcoming load to be transferred on it thus maintaining a neutral spine. However, in individual with low back pain due to impaired proprioceptive deficits  this biofeedback is delayed leading to excessive stress on structures of low back. Due to pain there is further proprioceptive deficit leading to a vicious cycle of pain and disability

Identifying muscle dysfunction

Local / deep muscles

Assessment of the function of the local/deep muscles is analogous with providing treatment. An understanding of the normal response is required for the abdominal drawing-in maneuver (transversus abdominis), isometric activation of multifidus, normal breathing (diaphragm), and pelvic floor activation.

Global/superficial muscles

There is a wide range of tests for the dysfunction of the global muscles regarding core stability/motor control. There are definitive texts on this topic as well as specific tests listed below:

1. Prone instability test
2. Prone extension endurance test (Biering-Sorenson paraspinal endurance strength)
3. Side bridge endurance test (quadratus lumborum endurance strength)
4. Pelvic bridging
5. Leg lowering test (lower abdominal strength)
6. Trunk curl
7. Hip external rotation strength
8. Modified Trendelenburg test (single leg squat with observation in the frontal plane)
9. Single leg squat in the sagittal plane
10. Single leg squat in the transverse plane

These tests for local and global muscle function should be applied and interpreted using clinical reasoning principles within a broad understanding of normal/abnormal motor control. There is preliminary evidence for a clinical prediction rule identifying people with low back problems more likely to respond to specific motor control/specific muscle activation of the local muscles :

• Younger age (<40)
• Greater general flexibility (hamstring length greater than 90°, postpartum)
• Positive prone instability test
• Presence of aberrant movement during spinal range of motion (painful arc of motion, abnormal lumbopelvic rhythm, and using arms on thighs for support)

Management principles

Here are some examples of exercises to improve the motor control /core stability of the lumbar spine.

Local/deep muscles

People with significant pathology where there is local muscle dysfunction, are likely to retrain a specific motor control before moving into more global training.

Global /superficial muscles

It is important for practitioners/sports personnel attempting to global/superficial muscle strength to have a clear understanding of any pathoanatomical problems that may be positively or negatively affected by such exercise. Ideally, all of these exercises should be done with correct lumbopelvic posture and control of the local/deep muscles. With most of these exercises duration of hold and repetitions can be varied (depending on the aim of the retraining/strengthing program) provided the exercise is done with good control.

Crunches- Lie supine on the floor with your knees bent, arms crossed over your chest and the feet flat on the floor. Then lift your shoulders from the ground and curl your stomach. Avoid a full sit up and ensure the low back remains in contact with the floor.

Obliques crunches - As per a normal crunch but leading with one shoulder towards the opposite knee (alternate sides each repetition).

Plank - Lie prone on the floor. Then while keeping your whole trunk straight (like a plank) lift up onto your forearms, with the elbows right under the shoulders, and toes. Hold this position as long as possible with control. To make the exercise more difficult try to lift one leg slightly of the ground. Balls/balance devices can also be used under the arms or feet. The plank can also be done on your side while supported by your feet and your forearm with your shoulder above your elbow.

Bridges - Lie supine with your knees bent and the feet flat on the floor. Lift your pelvis off the ground while supporting on your feet and shoulders. The bridge can be progressed by lifting one foot off the ground end extending the knee.

Hamstring raises/ Bird Dog leg only- Balance on your hands and knees with your back flat and your arms/thighs perpendicular to the floor. Raise one leg behind you until it is horizontal. Alternate.

Superman – As per a hamstring raise but progress by lifting the opposite arm to a horizontal position at the same time. Alternate.

Leg raises - Lie on your back with your legs straight and your arms by your sides. Then lift one leg 4 inches of the ground. Your back has to stay flat on the floor. Don’t allow it to arch. Alternate. The exercise can be progressed by lifting both legs at the same time.

Hundreds - Lie on your back with your legs straight and your arms by your sides. Then lift both legs so that they form a right angle in the hip and knees. Lift your arm straight a few inches off the ground. Focus on keeping your hips and legs completely still and your back flat.

There are also multiple exercises that can be performed with a physioball. The exercises were proven to have a greater gain of torso balance and neural activity than regular floor exercises.

Akuthota et al gave an example of how to build up a program with these exercises

• Go over the anatomy of the core
• Active participation emphasized
• Local/deep muscle activation – progress once able to perform 30 reps with 8 second hold.
• Abdominal bracing
• Bracing with heel slides
• Bracing with leg lifts
• Bracing with bridging
• Bracing in standing
• Bracing with standing row
• Bracing with walking Paraspinals/multifidis (advance if able to perform 30 reps with 8 s hold)
• Quadruped arm lifts with bracing
• Quadruped leg lifts with bracing
• Quadruped alternate arm and legs lifts with bracing
• Quadratus lumborum and obliques (advance if able to perform 30 reps with 8 s hold)
• Side plank with knees flexed
• Side plank with knees extended
• Trunk curl Facilitation techniques if necessary (pelvic floor contraction, visualization, palpation, identifying substitution patterns like pelvic tilt, ultrasound)
• Functional training positions with activation of the core

Summary

There is no single muscle or single exercise for low back problems and motor control/core stability as a treatment. At a minimum practitioners/sports personnel should be aware of key concepts in motor control and exercise and follow an evidence-based approach to exercise prescription.

Currently, there is strong evidence for specific motor control/specific muscle activation in isolation, progressing to more global and functional exercises.