Core Exercise and Spinal Stability

Article by: Benjamin Lee, MSc.

Exercise is considered the “gold standard” in the management of clients with low back-related pain and disability. However, not all core exercises are created equal. Traditional core exercises, which involve creating motion about the spine (i.e., crunches, side bends), may worsen your client’s condition because of excessive spine loads created in combination with repetitive segmental spinal motion. However, spine-sparing core exercises which impose minimal spine loads and motion (i.e., McGill’s “Big 3”) have been shown to be safe and effective for patients1,2. Before rehabilitation occurs, the patient’s functional goals (activity requirements) and functional deficits (relevant impairments) should be identified. This provides a start and end for the exercise prescription, with the ability to progress challenge based on their functional goals. This article will go over the science and anatomy of the ‘core’ muscles, rationale of certain core exercises over others, and how to coach a few basic but highly effective exercises.

Core exercises—defined as exercises that challenge the core musculature (muscles of the torso proximal to the ball and socket joints that help stabilize the spine)—are a staple among athletically trained individuals and clinical populations because of the exercises’ ability to strengthen musculature,3,4 improve muscular endurance,5 reduce low back pain (LBP),6-8 and improve sport performance.9-11 The mechanism of how these exercises stabilize the spine is thought to be from enhancing stiffness of the core muscles.12,13 Greater core stiffness enhances performance through three mechanisms.

As explained by world renowned spine biomechanist, Dr. Stuart McGill:

(a) briefly stiffening the torso proximal to the shoulders and hips transfers the full force and movement of muscles to the distal side of these ball and socket joints, resulting in greater limb strength and speed;
(b) muscularly stiffening the spinal column enhances its load bearing capacity, preventing buckling; and
(c) the muscular turgor associated with stiffness creates an armor over vital structures (i.e., internal organs) enhancing resilience during contact sports.10

The reason core stiffness is such an important concept is because it creates spinal stability. Without accounting for stability, almost all human activities could not be successfully performed. Three major tenets with regard to stiffness and stability exist for human function17:

  1. Sufficient stiffness allows for the body and spine to bear load.
  2. Stiffness and stability are related through muscular mechanisms, creating a guy wire system for the spine.
  3. Proximal stiffness may allow for distal mobility

In the context of the spine, mechanical engineer and biomechanist Anders Bergmark, described the stability–stiffness continuum using a spring-mass system: the stability of a system (spine) is dependent on the stiffness of the springs that attach to it (the “core” muscles, i.e., rectus abdominis, quadratus lumborum, internal and external obliques) (Fig. 1).18

How Muscles Stabilize the Spine

The concepts of stability and stiffness are benchmarks for all human motion, including spine function. Unlike the muscles of your limbs, the core musculature is composed of numerous layers of short, thick muscles designed to stabilize the spine and prevent excessive motions.

Figure 2: Comparing the core muscles to a barrel

When we look at the architecture of the torso these muscles act in a way like how hoops around a barrel generate ‘hoop stresses’ to keep the barrel from falling apart when filled.

External perturbation (i.e., externally applied loads or movements) can potentially disrupt the equilibrium of the system, like strong winds perturbing a radio tower. To maintain static equilibrium (ensuring the spine experiences no unwanted motion), the core muscles must generate sufficient stiffness. This is akin to how the rigging on a ship stabilizes its mast (Fig. 2). The stiffness of the “guy wires” provides stability to the mast to ensure it stays upright against external forces such as the wind or rocking of the ship. Similarly, stiffness generated by the core muscles helps to “anchor” the spine, enhancing its ability to resist external perturbation. Insufficient stiffness of the guy wires may cause the mast to fall over or buckle if excessive perturbations are applied. Similarly, insufficient core stiffness will cause the system to mechanically buckle, resulting in an involuntary bending of the spine when trying to resist external perturbation (i.e., yielding during a heavy deadlift).

Figure 3: The same core muscles stabilize the spine like how guy wires stabilize the mast of a ship

Exercise Selection

Now that we better understand how the core muscles work, how do we go about training them? Going back to our barrel example, to optimally train the core muscles, it would make sense to not train like them like your limb muscles (i.e. biceps, hamstrings) by taking them through a long range of motion, but instead to challenge them in stabilizing the torso (prevent your spine from bending) under load or awkward postures.

For those of you reading who enjoy videogaming, I think of exercise selection is an action roleplaying game – before I can start doing any jumps or weighted carries or anything else fancy, I first have to devote my EXP points into mastering basic skills. Here are is the start point of ANY core-focused program: three exercises that will train isometric/static core stability:

Plank

Figure 4: Plank demo

The plank challenges primarily the anterior core muscles (rectus abdominis) to prevent the spine from hyperextending. When the body is held in an extended posture like this, the rectus abdominis (aka your ab muscles) work like a Roman arch to support your spine.

Figure 5: Roman arches supporting a bridge. Your core muscles work like the arches to support the bridge that is your torso

To perform the plank, simply lie face down and balance on your toes and forearms. Keep your back straight resisting the urge to hike your hips into the air or let them sag to the floor.

Without the core muscles working, gravity would pull your hips down to the floor creating hyperextension of the low back, which can be a mechanism of pain for some types of clients. During the plank you can get extra activation by:

  • Actively bracing your abdominals (imagine stiffening them like someone is going to punch you in your stomach)
  • Squeezing your glute muscles (like you’re trying to hold a one hundred dollar bill between them)
  • Squeezing your fists
  • Statically pulling your elbows toward your waist

Start with performing multiple 10 second holds (i.e. 5 x 10 sec). If this is easy, add a second set of 4 x 10 sec holds, then a third set of 3 x 10 sec holds, etc.

Side Bridge

Figure 6: Side bridge from the knees demo

The side bridge challenges the lateral core and glute musculature to hold your body in place when balanced on your side.

Begin on your side resting on your knees with your hips bent and bottom forearm supporting you. To initiate the side bridge, simply drive your hips forward so that your torso is off the floor and hips are completely straight.

Similar to the plank, these muscles work like a Roman arch to prevent your hips from sagging to the ground and spine laterally bending. You can use the exact same cues from your plank to get more activation out of your muscles with the same set/rep scheme. This doing this from the knees is easy, progress to your feet with your top leg in front of your bottom leg.

Figure 7: Foot placement for the side bridge from the feet

Bird Dog

Figure 8: Bird Dog demo

The bird dog is a rotational core stability exercise. It challenges the muscles of your back (upper back, low back, glutes) to prevent the body from rotating as you hold the outstretched position.

Begin the bird dog on your hands and knees. Ensure your spine is neutral without excessive rounding or arching. From here, use a light core brace and then drive the opposite arm and leg out in front and behind you, respectively. Hold this outstretched position without losing balance.

During the bird dog you can get extra activation by:

  • Actively bracing your abdominals (imagine stiffening them like someone is going to punch you in your stomach)
  • Squeezing your extended leg’s glute muscle while driving out your heel/pulling your toes toward your knee
  • Squeezing your fist

 

About the Author:

Benjamin Lee is a formally trained Mechanical Engineer (BASc ’09, University of Waterloo) whose passion for fitness and athletics led him to pursue a master’s degree in Biomechanics (MSc. ’13, University of Waterloo). His research on the assessment and prescription of exercise for low back injury prevention/rehabilitation was supervised by the world-renowned professor, Dr. Stuart McGill. Ben has published numerous ground-breaking academic papers and textbook chapters on this topic, lectured to thousands of healthcare professionals, and has worked with a variety of clients ranging from office workers to elite professional athletes. Ben applies his knowledge as Chief Scientific Officer of Fortius Labs, developing revolutionary artificial intelligence software to help health & fitness professionals objectively assess their clients’ training needs and develop data-driven corrective exercise programs.

References

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  2. McGill SM. Low back stability: from formal description to issues for performance and rehabilitation. Exerc Sport Sci Rev. 2001;29(1):26-31.
  3. Norris CM. Abdominal muscle training in sport. Br J Sports Med. 1993;27(1):19-27.
  4. Willett GM, Hyde JE, Uhrlaub MB, Wendel CL, Karst GM. Relative activity of abdominal muscles during commonly prescribed strengthening exercises. J Strength Cond Res. 2001;15(4):480-485.
  5. McGill SM, Childs A, Liebenson C. Endurance times for low back stabilization exercises: clinical targets for testing and training from a normal database. Arch Phys Med Rehabil. 1998;80(8):941-944.
  6. Gardner-Morse MG, Stokes IA. The effects of abdominal muscle coactivation on lumbar spine stability. Spine. 1998;23:86-92.
  7. Morgan D. Concepts in functional training and postural stabilization for the low-back-injured. Top Acute Care Trauma Rehabil. 1988;2:8-17.
  8. O’Sullivan P, Twomey L, Allison G. Evaluation of specific stabilizing exercise in the treatment of chronic low back pain with radiologic diagnosis of spondylolysis or spondylolisthesis. Spine. 1997;24:2959-2967.
  9. Hedrick A. Using uncommon implements in the training programs of athletes. Strength Cond J. 2003;25(4):18-22.
  10. McGill SM. Ultimate Back Fitness and Performance. 5th ed. Waterloo, Canada: Backfitpro Inc; 2014.
  11. Willardson JM. Core stability training: applications to sports conditioning programs. J Strength Cond Res. 2007;21(3):979.
  12. Lee BC, McGill SM. Effect of long-term isometric training on core/torso stiffness. J Strength Cond Res. 2015;29:1515-1526.
  13. Lee B, McGill S. The effect of short-term isometric training on core/torso stiffness. J Sports Sci. 2017;35:1724-1733.
  14. McGill SM. Low Back Disorders. 3rd ed. Champaign, IL: Human Kinetics; 2015:56.
  15. Bergmark A. Stability of the lumbar spine: a study in mechanical engineering. Acta Orthop Scand. 1989;60:1-54.

 

 

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