Core strength: Dynamic Core Strength v Core Stiffness
Dr. Stuart McGill of Waterloo University is probably the world authority on low back injuries. Over the past few decades he has written extensively on the topic of back injuries and the concept of core stability (in books such as Ultimate Back Fitness and Performance and Back Mechanicas well as in countless professional journals articles – visit www.backfitpro.com) (1). I have had the privilege of attending several of his talks at different conventions and attended his back pain seminar. This blog is just an insight and introduction into effective core stability training.
Doing thousands of crunches and V-sits in an attempt to obtain six pack is one thing. But training for optimum athletic performance and eliminating lower back pain to build your body to become more resilient to future injury requires a different and more specific approach.
To initiate this athletic optimum training approach, we need to start by learning about our body’s ‘core’ and how it’s function relates to both the cause and rehabilitation of lower back injuries.
What is ‘core stability?’
Visualise a concert orchestra combined of different groups of instruments. Every musician must play their instruments in sync with constant changes in tempo and volume. Much like the symphony orchestra illustration, each and every muscle of the core has a role to play. Your body must be able to coordinate each muscle to create precise movement. It has to control: limb velocity, movement, load on a limb, and limb limits and balance. It must stabilise the whole system using kinaesthesia mediated by proprioceptors, mechanosensory neurons located within muscles, tendons and joints, to create an overall representation of body position, movement, and acceleration.
The body's core region is sometimes referred to as the torso or the trunk, (although there are some differences in the muscles identified as constituting them). The major muscles involved in core stability include the pelvic floor muscles, transversus abdominis, multifidus, internal and external obliques, rectus abdominis. The erector muscles of the back such as erector spinae (sacrospinalis) especially the longissimus thoracis, the diaphragm, and the larger muscles that span multiple joints (like the lats and psoas muscles). The glutes are also an important part of the ‘core’. Each and every one of these muscles must coordinate together in order to enhance the stability of the spine
But what really is ‘stability’?
Professor McGill has been able to define and measure Spinal stability with his work. When muscles contract they create force and stiffness. It is the stiffness part that is vital for stability.
Think of the spine as a ships mast that needs to be stiffened to bear load using rigging ropes. This is the role of the muscles to act as the rigging ropes. Through his research, he has measured athletes who fail to obtain appropriate muscular stiffness around the spine by coordinating muscle activation, and their subsequent injuries and pain.
Distal movement requires proximal stiffness
Our body functions as a coordinated unit, think about trying to flex your elbow quickly. The shoulder needed to be stiffened otherwise the entire arm would move. Now using the same principle think about walking. The pelvis must be stiffened to the spine otherwise the left hip would fall as the left leg swings forward to take a step. This core stiffness is non-negotiable to enable walking. Thus all body movement needs appropriate coordination of muscles. To move, run, or squat requires spine stiffness and core stability.
When the core muscles fails to meet the demands placed on the body to stabilise effectively during a certain lift, elements of the spine will be overloaded with forces that increase injury risk and performance will be degraded. Much like a musician playing out of tune it would instantly ruin the entire orchestral piece, each and every muscle that surrounds the spine must play it’s part in maintaining our body’s own “symphony of movement” in order to produce safe and powerful movement.
The difference between core strength and core stiffness
There are two general approaches many will take to address a weak link of the core. The first is dynamic strengthening exercises such as crunches, sit-ups, lying hyper extensions, side plank crunches, V-sits or Russian twists (commonly used by PTs in fitness clubs around the globe). Old school thinking by coaches and medical practitioners was that by build strength through flexion and extension movement, these exercises would create a stronger core that would give the spine less chance for buckling and breaking under tension.
This is partially true; the core muscle do need to have sufficient amount of strength to contract and ‘turn on’. Stiffness is created when these core muscles contract. Much like a rigging rope that attaches and holds up a ships mast, each muscle that surrounds the spine must provide a certain amount of tension and stiffness to maintain the strength of the spine as a whole and keep it from buckling and becoming injured.
What most people don’t appreciate is… the majority of people who develop lower back pain already have strong backs (4). While exercises like lying hyper extensions, sit-ups or back extensions may be great at increasing strength, they do little to increase core stiffness (8). To enhance the quality of core stiffness, you must train the core differently. In order to obtain high level of core stiffness you must train with isometric exercises built to enhance muscular endurance and coordination.
An ‘Isometric’ contraction occurs when muscle length remains relatively constant as tension is produced but there is no change in the joints they cross. An example of this would be during a side plank. The lateral oblique and quadratus lumborum (QL) muscles are very active yet the spine and hips remain static and do not move. Research has found that isometric exercises to enhance muscular endurance are far superior when compared to dynamic strengthening exercises in enhancing spinal stiffness and stability (making them ideal not only for rehabilitation of back injuries but also in the training and enhancement of athletic performance) (8)
The core muscles function is to limit excessive motion rather than creating it. If the core muscles were evolved to create movement they would be long like the quads muscles of the legs, but they aren’t. Look at the rectus abdominis, with the linea alba and the tendinous intersection that create 6 muscles panels. It has evolved to optimally create stiffness rather than movement. This is the same with the erector spinae in the back that only cross 2-3 vertebral bodies (joints). The multifidus muscle (like the rectus abdominis) has high cross section area so its force generating capacity is high and has a low fibre length so its muscle excursion is low. Showing that the multifidus muscle is designed to provide spinal stability.
The old-school way of thinking, in which physios and personal trainers addressed the core for years has been sub-optimal. This is why someone can display a ripped six-pack and yet still have poor core stability when it comes to athletic performance, deadlifting or squatting.
In order to stiffen the core and limit excessive motion, every muscle of the core, (glutes, transversus abdominis, multifidus, internal and external obliques, rectus abdominis etc) must co-contract and work together.
When this is done correctly through a bracing action, your body creates it’s natural “weightlifting belt.”
By creating a stiff core around your spine it transfers force throughout your body and allows you to be able to lift maximal weight safely and efficiently. An example of this would be a powerlifter performing a max effort deadlift requires sufficient core stability in order to transfer the power they generates from their legs through the core and into the upward drive of the bar.
Much like the orchestra illustration at the start, each and every muscle of the core has a role to play, but none is more important than the other. For this reason, proper stability training should not focus on one specific muscle. For decades, physios, pilates instructors, chiropractor etc, were incorrectly taught to focus and isolate certain muscles such as the transverse abdominus (TVA), multifidus, or QL in an effort to enhance core stability. (Pilates is still preaching TVA despite all the research). This method however, is flawed for a number of reasons.
Research has shown it is impossible for an individual to solely activate one specific muscle of the core.
Despite what your physiotherapist or doctor says, you cannot train your multifidus, QL or even your TA muscle in isolation.
Even it were possible to target a specific muscle of the core (as some would argue is possible through exercises like abdominal hollowing), methods like this have been shown to be far less efficient in creating stability for the spine compared to abdominal bracing (contracting all of the core muscles together) (15).
How to train to stiffen your core!
There is unfortunately no ‘cookie cutter’ program when it comes to core exercises because there is no one universal movement that equally stresses all of the muscles that surround your spine. Consequently, we must utilise a range of exercises to efficiently work all of them.
Throughout his research Dr. McGill has found there to be three specific exercises that most efficiently address all of these areas without placing excessive stresses on the parts of the back that may be aggravated or irritated due to injury. This group of exercises has famously become known as ‘The Big 3.’
Curl-Up
Side Plank
Bird-Dog
Curl Up, Side Plank and Bird Dog
These 3 exercises are excellently demonstrated by Dr. Aaron Horschig, PT, DPT, CSCS, USAW at Squat University on YouTube 3 Core Exercises You Should Do EVERYDAY!
Hopefully this has given you a better understanding of optimal core stability training and the difference between dynamic core training (six pack) and optimal core stiffness training for spinal health, lower back pain and sporting performance.
References
McGill SM. Ultimate Back Fitness and Performance (4thed). Waterloo, Canada: Backfitpro Inc, 2009. (www.backfitpro.com)
McGill, SM. Back Mechanic: The step by step McGill Method to fix back pain. Backfitpro Inc. 2015 (www.backfitpro.com)
McGill SM. Core training: evidence translating to better performance and injury prevention. Strength and Conditioning Journal. 2010; 32(3): 33-46
McGill SM. Grenier S, Bluhm M, Preuss R, et al. Previous history of LBP with work loss is related to lingering effects in biomechanical physiological, personal, and psychosocial characteristics. Ergonomics. 2003;46:731-746
Indahl A, Kaigle A, Reikeras O, Holm S. Electromyographic response of the porcine multifidus musculature after nerve stimulation. Spine. 1995;20(24):2652-8
Cohen SP & Raja SN. Pathogenesis, diagnosis, and treatment of lumbar zygapophysial (facet) joint pain. Anesthesiology. 2007;106:591-614
Durall CJ, Udermann BE, Johansen DR, et al. The effect of preseason trunk muscle training of low back pain occurrence in women collegiate gymnastics. J Strength Cond Res. 2009;23:86-92
Lee BC, McGill SM. Effect of long-term isometric training on core/torso stiffness. JSCR. 215;29(6):1515-1526
Cholewicki J, McGill SM, and Norman RW. Lumbar spine loads during lifting of extremely heavy weights. Med Sci Sports Exerc. 1991;23:1179-1186
McGill SM, Cholewicki J. Biomechanical basis for stability: an explanation to enhance clinical utility. JOSPT. 2001;31(2):96-100
McGill SM. Stability: from biomechanical concept to chiropractic practice. J Can Chiropr Assoc. 1999;43(2)
Boren K, Conrey C, Le Coguic, et al. Electromyographic analysis of gluteus medius and gluteus maximus during rehabilitation exericses. Int J Sports Phys Ther. 2011;6(3):206-223
McGill SM. Low Back Disorders: Eevidence Based Prevention and Rehabilitation(2nd ed). Champaign, IL: Human Kinetics Publishers, 2007.
Olfat M, Perry J, Hislop H. Relationship between wire EMG activity, muscle length, and torque of the hamstrings. Clin Biomec. 2002;17(8):569-579
Grenier SG, McGill SM. Quantification of lumbar stability by using 2 different abdominal activation strategies. Arch Phys Rehabil. 2007;88(1):54-62
Juker D, McGill SM, Kropf P, Steffen T. Quantitative intramuscular myoelectric activity of lumbar portions of psoas and the abdominal wall during a wide variety of tasks. Mec Sci Sports Exerc. 1998;30:301-310
McGill SM. The mechanics of torso flexion: sit-ups and standing dynamic flexion maneuvers. Clinical Biomechanics. 1995;10:184-192
