Article Reviewed
McGill, S. M. (2001). Low Back Stability: From Formal Description to Issues for Performance and Rehabilitation. Exercise and Sport Science Reviews. 29, 26-31.

Introduction
In the world of fitness, the terms ‘core function’, ‘core strength’, and ‘core stability’ have become modern day terms in exercise program design. Client exercise prescriptions now include exercises specific for the ‘critical torso muscles’ (e.g., transverse abdominins and multifidus muscles), posture/spinal assessments, training movements to correct muscle imbalances, and new concepts for training the ‘global’ abdominal muscles (rectus abdominis and obliques). However, much of the exercise design is based on ‘bits an pieces’ of the research on low back stability. Most recently, Stuart McGill, one of the leading researchers in the world on low back stability authored a review article on this topic to “develop a synthesis of the scientific foundation of the notion of stability as it pertains to the lumbar spine and then to provide specific guidelines for enhancing stability to advance rehabilitation and athletic performance.” Highlights of this review article will be discussed in this article.

The Unstable Spine
How do injuries to the low back occur from such seemingly simple tasks as bending over to pick something off the floor? Research now shows that nominal daily tasks, as well as strenuous bodily exertions, may result in a spine ‘buckling’ (McGill, 2001). Computerized analysis of this phenomenon suggests that there is a momentary reduction in neural activation to one or more of the deep intervetebral muscles, resulting in this spinal segmental ‘buckling’ (slight rotation of a spinal segment), leading to tissue irritation or injury. Therefore, the musculature must be trained to “stiffen the spine against buckling” (McGill, 200). However, when prescribing low back exercise programs for the many levels of fitness abilities, and realizing the different demands people place on their bodies, determining an optimal balance of stability and mobility becomes quite challenging.

The Stable Spine
Considering that spinal joints can rotate in the sagital, frontal and horizontal plane, as well move along the three axes of these planes, the goals of creating a stable spine are multidimensional. It should be noted that all joints have an inherent ‘joint stiffness’, which is attributable to the passive joint capsules and surrounding ligaments (McGill, 2001). In addition, the motor control system to the muscles is able to control stability of the joints through coordinated muscle coactiviation (McGill, 2001). However, as introduced in the section above, a defective motor control system can lead to the temporary ‘buckling affect’ of an intersegmental joint, and subsequent injury. McGill suggests that the preventative objective is to attain ‘sufficient stability’, which directly relates to optimal stability and mobility with no compromise to the spine. This can be attained with exercises that provide coactivation of the deep intrinsic spinal muscles and abdominal wall (transverse abdominis).
Introducing the Main Lumbar Spine Stabilizers
Identifying the functional roles of the significant spinal stabilizers requires deep intramuscular electrode studies, which are quite challenging to successfully complete. Developing mathematical models of the spinal muscular doing activities is another way of estimating muscle involvement and activation. However, the use of both of these investigative techniques suggests that the important intrinsic muscles of the spine include the multifidus, quadradus lumborum, longissimus, and iliocostalis as well as the transverse abdominins (McGill, 2001).

The Low Back Training Program
From McGill’s research on low back stability, the data suggest that the healthiest training intervention for the spinal flexors involves muscular endurance versus strength training. McGill states that “the safest and mechanically most justifiable approach to enhancing lumbar stability through exercise entails a philosophical approach consistent with endurance, not strength; that ensures a neutral spine posture when under load (or more specifically avoids end range positions) and that encourages abdominal muscle cocontraction and bracing in a functional way.” Bracing is a neurophysiological phenomenon involving cocontraction of the abdominal wall and deep intrinsic muscles of the spine in an effort to better stabilize the low back.

Flexion-Extension “Cat-Camel” Warm-up
McGill and colleagues recommend beginning the low back stability program with about six flexion-extension cycles of the “cat-camel” exercise. This is done not as a stretch, but as a mobility exercise to reduce any present stresses on the spine.

Quadratus Lumborum Training
For quadratus lumborum training, McGill recommends the horizontal isometric side bridge which can be done from a knee supporting position on the floor or a more challenging version which utilizes a feet supported version. Another advanced version that involves a maximal involvement of the quadratus lumborum, obliques, with cocontraction of the critical spine muscles and transverse abdominis is the rolling side bridge.

Rectus Abdominis, Obliques, and Transverse Abdominis Training
Dr. McGill notes that there is no single abdominal exercise that effectively challenges all of the abdominal musculature. He therefore recommends several versions of curl-ups (or crunches) for the rectus abdominis and obliques in conjuction with the quadratus lumborum exercises. The article suggests to avoid sit-up exercises with bent and straight legs due to the high psoas activation and compressive loads on the low back. Leg raises also cause a great deal of psoas activation and spine compression.

Back Extensor Training
Front lying (prone) upper torso (or leg) lifts off the floor may not be safely indicated for persons with low back pain. These exercises may place to much load on the spine. One alternative exercise McGill recommends in his review is the “Bird-Dog” exercise. This exercise adequately engages the longissimus, iliocostalis, and mutifidus muscles of the spine, with much less stress to the spinal segments.

Stability Training Concepts
When designing low back stability programs, keep in mind that the optimal goal is training the spinal extensors and flexors for ‘sufficient stability.” McGill suggests that to accomplish this goal with the torso musculature, programs should be designed to enhance muscular endurance, rather than muscular strength. Try to balance the amount of exercises you do for the spinal flexors and extensor exercises. The lateral musculature exercises should get about 75% of the time allotted the spinal extensors (McGill, 2001). Finally, encourage your clients to continually learn how to draw in the abdominals, engaging the transverse abdominals. Hopefully, with this researched-based approach to low back stability training you will be sparing your clients spinal damage while helping to improve the quality of their active lifestyle.