The term core is bantered about in all corners of the health and fitness industry, yet to most people who use this word it remains a vague, almost nebulous description of supportive stomach and back muscles. We would like to solidify the term and provide a workable definition of the core, at least as we currently understand the term: The core muscles are the truncal muscles that support and stabilize the torso, protect the spine, and allow power transfer through the torso.
The core includes global stabilization muscles such as the transverse abdominis (TrA), the internal oblique (IO), and external oblique (EO); and intersegmental stabilizers such as the multifidus muscles.1 Since the list of muscles composing the core is a moving target depending on authorship, we would rather concentrate on core function than try to generate a composite list of the core muscles. However, certain muscles are central to any discussion of the core: the TrA, OI, OE, multifidus, rectus abdominis (RA), quadratus lumborum (QL), and the muscles of the erector spinae. Some would add the iliopsoas, latisimus dorsi, gluteal muscles, hip adductors, and hamstrings to this list.
The individual muscles of the core are each capable of contributing to several different functions, and no function is isolated to an individual muscle. The core is a complex and integrated network of muscles that work in synchrony to support the torso with stiffness and strength. It is impractical to try to isolate the function of individual muscles such as the TrA. In fact, when the core muscles stiffen in concert, their total strength surpasses the sum of the individual muscles.
In recent years, there has been a movement afoot that promotes abdominal hollowing,1 pulling in the abdominal muscles in an attempt to isolate the TrA and indirectly activate the multifidus muscles. Stuart McGill, PhD, has found that core bracing is superior to abdominal hollowing in regards to protecting the spine from injury. Vera-Garcia (with McGill as a co-author) found that hollowing actually inhibits the multifidus' response to perturbation,2 actually reducing core stabilization.
Your Internal Weight-Lifting Belt
Weight-training belts are no longer the rage they once were and their use is ebbing in most of the realm of physical culture. This is due in part to the knowledge that weight-lifting belts are not necessary. One study revealed that the advantage in using belts may come from perceived rather than actual protection and performance enhancement.3 Belts essentially increase the amount that lifters are willing to lift. Belts interfere with the natural intrinsic stabilization of the trunk without substantial benefit and should generally be avoided.4-9
We each possess a natural, built-in weight belt that is activated by the muscles of the core. Your intrinsic stabilization corset consists of a combination of the TrA and the thoracolumbar fascia. The posterior layer of the thoracolumbar fascia angles up away from the spine (Figure 1), whereas the anterior layer of the thoracolumbar fascia angles down and away from the spine (Figure 2). They both are joined to the TrA by the lateral raphe. So, when the TrA stiffens, the contraction produces a Poisson's effect,10 which causes the spinous processes to approximate in a protective manner (Figures 3 and 4).11
A collateral benefit of TrA contraction is activation of the multifidus muscle.12 The multifidus provides intersegmental stabilization through its stiffening effect, but is difficult to contract voluntarily. Together, the global and intersegmental stabilizers protect the spine from excessive shear and torsional forces.13
Bracing the Core With Muscular Stiffness
Learning to brace the core is an important component in protecting the spine and enhancing athletic performance. While many athletes intuitively brace their core during athletic exertion, others require training. It takes only a few minutes to learn how to coax the core muscles into a protective stiffened brace, but may take months to imbed a permanent neurological groove of bracing into a particular athletic motion pattern.
Begin in a relaxed standing posture; place the fingertips of one hand on the lumbar paraspinal muscles just to the side of the spinous processes. The other hand should be positioned on the abdominal muscles at the level of the ASIS. Bend at the waist until you feel the muscles of your lower back contract under the fingers on your back. Note how this feels and then arch your spine until the spinal muscles relax under your fingers. While maintaining this position, stiffen the abdominal muscles as if you were about to be punched in the gut. You should feel your spinal muscles contract like they did when you bent over at the waist. Note how this feels with both hands. Practice engaging these muscles until it takes little conscious effort.
If bracing in this manner aggravates a spinal condition, reduce the degree of abdominal contraction. Maximal stiffness is not required. Practice in the range of 10 percent to 25 percent of maximal stiffening. Stiffening should accompany strenuous athletic exertion. When establishing neurological groove patterns for compound motor patterns, make sure to include bracing. For squatting motions, stiffen the core throughout the entire motion, even when no weight is used.
A dilemma that often accompanies core stiffening exercises is interference with diaphragmatic breathing. When first learning to stiffen the core, consciously engage in diaphragmatic breathing until it becomes routine. Once core bracing and diaphragmatic breathing are mastered, they should be practiced or rehearsed while in exertion-induced respiratory distress until it becomes natural. Practice performing cardiovascular interval training while concentrating on core bracing and diaphragmatic breathing. In time, these two activities will be imbedded in your neurology to the point of not requiring conscious intercession.
Core Stiffness Is Fundamental to Cross Fitness
Core bracing fits into one of the creeds of the cross-fitness movement: integration of compound motion patterns rather than muscle isolation. A properly functioning and reactive core is required for high levels of athleticism whether you are an elite athlete, a cross-fitness devotee, or even an average weekend golfer. Certainly cross-fitness injuries will be curtailed if athletes maintain proper form and utilize core bracing when performing athletic activities such as squatting, tire flipping, dead-lifting, plyometric jumping drills, kettlebell drills and agility drills. If our patients are going to engage in cross-fitness programs, it is our duty to prepare them properly through treatment, prevention and education.
- Richardson C, Jull G, et al. Therapeutic Exercise for Spinal Segmental Stabilization in Low Back Pain. Churchill Livingstone, Edinburgh, 1999:22-25.
- Vera-Garcia FJ, Elvira JL, Brown SH, McGill SM. Effects of abdominal stabilization maneuvers on the control of spine motion and stability against sudden trunk perturbations. J Electromyogr Kinesiol, 2006 Sep 20;17(5):556-67.
- McCoy MA, Congleton JJ, Johnston WL, Jiang BC. The role of lifting belts in manual lifting. Int J Ind Ergonomics, 1988;2:259-266.
- Majkowski GR, Jovag BW, Taylor BT, Taylor MS, Allison SC Stetts DM, Clayton RL. The effect of back belt use on isometric lifting force and fatigue of the lumbar paraspinal muscles. Spine, 1998;23(19):2104-2109.
- National Institute for Occupational Safety and Health. Workplace Use of Back Belts: Review and Recommendations. Rockville, MD: Department of Health and Human Services (National Institute of Occupational Safety and Health), Publication No. 94-122, 1994.
- Mitchell LV, Lawler FH, Bowen D, Mote W Asundi P, Purswell J. Effectiveness and cost-effectiveness of employer-issued back belts in areas of high risk for back injury. J Occup Med, 1994 Jan;36(1):90-94.
- Thomas JS, Lavender SA, Corcos DM, Andersson GB. Effect of lifting belts on trunk muscle activation during a suddenly applied load. Hum Factors, 1999 Dec;41(4):670-6.
- Reyna JR, Leggett SH, Kenny K, Holmes B, Mooney V. The effect of lumbar belts on isolated lumbar muscle strength and dynamic capacity. Spine, 1995;20(1)68-73.
- McGill SM, Norman RW, Sharratt MT. The effect of an abdominal belt on trunk muscle activity and intra-abdominal pressure during squat lifts. Ergonomics, 1990 Feb;33(2):147-60.
- See www.ecourses.ou.edu/cgi-bin/view_anime.cgi?file=m1421.swf&course=me&chap_sec=01.4
- Bogduk N. Clinical Anatomy of the Lumbar Spine and Sacrum, 3rd Edition. Churchill Livingstone, Edinburgh, 2001.
- Hides JA, Jull GA, Richardson CA. Long-term effects of specific stabilizing exercises for first-episode low back pain. Spine, 2001;26:E243-8.
- Moseley GL, Hodges PW, Gandevia SC. Deep & superficial fibers of lumbar multifidus are differentially active during voluntary arm movements. Spine, 2002;27(2):E29-36.
The views expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense or the U.S. government. This is the third in a series of articles addressing cross-fitness. Future articles will present foundational components of core stabilization and gluteal activation, as well as the prevention of shoulder injuries.
Dr. William Morgan, is the president of Parker University. He previously served as the White House chiropractor (2007-2016), and as the chiropractor to the United States Congress and Supreme Court (2000-2016). He was credentialed at Bethesda Naval and Walter Reed military hospitals, and was team chiropractor for the U.S. Naval Academy football team.
Dr. Chris Feil, a graduate of Palmer College of Chiropractic, has an undergraduate degree in exercise physiology and completed a multidisciplinary internship at the National Naval Medical Center in Bethesda, Maryland. He practices in Baltimore.