Principles of Core Stabilization for Athletic Populations

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1 Principles of Core Stabilization for Athletic Populations R. BARRY DALE, PhD, PT, ATC, CSCS University of South Alabama RYAN LAWRENCE, DC Saraland Chiropractic, Saraland, AL Key Points Core strengthening, or stabilization, has become an important topic in athletic strengthening, conditioning, and rehabilitation. The term describes muscular control of the axial skeleton (namely, the lumbar spine and pelvic girdle) to maintain functional stability. In fact, proximal stability is requisite for distal mobility of the extremities and implies that successful extremity movement relies on trunk stability. 1 For example, every booming drive from a professional golfer or the explosive swing of the bat from a Major League Baseball player requires the spine, along with its related structures, to endure tremendous stress and produce exorbitant force. The stress imposed and the force produced within the trunk are often associated with inertia from the lower extremities that passes through the trunk into the upper extremities during functional or sport-specific movements. 2 Unfortunately, many athletes focus strength training and exercise around their extremities, overlooking the vast importance of a strong, stable core. Achieving core stability is a multifactorial process dependent on at least four mechanisms: rapid activation of the pri- Core stabilization is multifaceted and requires muscle strength, local muscle endurance, neuromuscular control, and coordination of multiple trunk muscles. Exercises and activities that activate core musculature can be somewhat different from traditional trunk exercises. More research in the form of outcomebased studies is needed to ascertain the effectiveness of core stabilization in treating and preventing low back pain. Key Words: lumbar stability, trunk musculature, abdominal exercise mary spinal stabilizer muscles, coordinated muscle cocontraction, sufficient strength of volitional muscles, and requisite endurance. 3,4 Core stability requires healthy functioning of the central nervous system, which constantly receives dynamic afferent input from the mechanoreceptors and proprioceptors of the joints, muscles, and ligaments. The central nervous system integrates this information and uses it to orchestrate the muscular system for proper coordination, posture, and movement. It is evident that true core stabilization is the harmony of osteoligamentous structures and the neuromuscular system. Research and evidenced-based guidelines pertaining to core stability are relatively scarce. The clinical rationale for adopting a training regimen addressing core stabilization, however, purports numerous benefits to the athlete, including enhancing performance, correcting postural imbalances, preventing injuries, and aiding in the corrective treatment of trunk injuries. The preceding article in this issue presented definitional, historical, and background information on core stabilization. The purpose of this article is to briefly review the anatomy of the core musculature, present the various principles and scientific evidence supporting the application of core-stabilization techniques, and provide examples of various exercises for athletes. A complete presentation of core stabilization is beyond the scope of the article, and the reader is referred elsewhere for more information on the topic. 2, Human Kinetics ATT 10(4), pp ATHLETIC THERAPY TODAY JULY

2 Abdominal Musculature Core Stability Muscles of the abdominal wall and in the abdominal cavity contribute to lumbar-spine stability. These muscles include the rectus abdominis, internal and external obliques, transverse abdominis, diaphragm, the pelvic-floor muscles, quadratus lumborum, and psoas major. Table 1 summarizes the actions of these muscles. The rectus abdominis and obliques directly contribute to lumbar stability. Their common flexor torque opposes extension, and they act to support the trunk during unexpected changes in postural stability. During lifting activities, the abdominals contract simultaneously with the lumbar extensors. Although the rectus abdominis is a powerful trunk flexor that limits lumbar extension via eccentric action, it does not contribute to trunk rotation or lateral flexion, and its activity is not associated with increased abdominal pressure. Internal oblique activity limits contralateral trunk rotation and lateral flexion and contributes to controlling trunk extension. External oblique activity also controls sameside rotation and contralateral lateral flexion. 2,5 Isolated activity of the transverse abdominis might directly stabilize the lumbar spine. Although there is some controversy over the role of the transverse abdominis with respect to core stability, there is evidence to suggest that its activity contributes to increased intra-abdominal pressure, which thereby helps stabilize the spine. 5 Intra-abdominal pressure is important because it produces an extensor moment on the spine that facilitates the performance of functional activities associated with lifting. 5 In addition, combined activity of the transverse abdominis and the internal oblique acts to limit translation and rotation, which serves to stabilize the lumbar spine. 2 Transverse abdominis activity also directly stabilizes the sacroiliac joint. 5,8 The diaphragm and other muscles of the posterior abdominal wall and pelvic floor contribute to lumbar stability by direct or indirect means. Contraction of the diaphragm increases intra-abdominal pressure. The quadratus lumborum provides stability to the lumbar spine by resisting buckling-type forces during lifting or carrying, but it becomes hyperactive in individuals with low back pain. Activity of the psoas major, especially in its posterior portion, also controls vertebral Table 1. Trunk Muscles Composing the Core 2,5 Core Region Muscle Functional Contribution to Core Stabilization Superior wall Diaphragm Increases intra-abdominal pressure (IAP). Inferior wall Psoas major Trunk flexor and ipsilateral rotator when lower extremities are stationary. Pelvic floor Helps modulate IAP. Posterior wall Multifidus Multisegment stabilizers. Longissimus Lumbar extensor. Iliocostalis Intertranversarii Transverse abdominis Quadratus lumborum Gluteus maximus Lumbar extensor. Ipsilateral lateral trunk flexor. Increases IAP, stabilizes sacroiliac joint; coactivation with internal oblique limits translation and rotation. Ipsilateral trunk lateral flexor, isometric lumbar stabilizer. Trunk extensor when lower extremities are stationary. Anterior wall Rectus abdominis Trunk flexor, controls extension. External oblique Internal oblique Trunk flexor, controls extension; contralateral rotator, controls ipsilateral rotation; ipsilateral lateral flexor, controls contralateral flexion. Trunk flexor, controls extension; ipsilateral rotator, controls contralateral rotation; contralateral lateral flexor, controls ipsilateral flexion. 14 JULY 2005 ATHLETIC THERAPY TODAY

3 motion. Because psoas inflexibility can contribute to low back pain, psoas stretching might be appropriate in the presence of low back pain. The pelvic floor contributes to lumbar stability by acting to increase intra-abdominal pressure. 5 Lumbar Musculature Lumbar muscles associated with lumbar stability include the multifidus, longissimus thoracis pars lumborum, iliocostalis lumborum pars lumborum, and intertranversarii. Table 1 summarizes the actions of the various muscles associated with lumbar stability. The primary stabilizing muscles of the core are the lumbar multifidi. The lumbar multifidi span vertebrae from segment to segment, surrounding and protecting the facet joints by applying traction force to their articular capsules, thereby preventing impingement during spinal movement. Thus, their primary function is not to conduct movement of the spine but to stabilize it to protect its integrity while other muscles are involved in trunk movement. Cholewicki and McGill found that the deep fibers of the multifidi undergo minimal changes in length throughout lumbar range of motion. 9 This suggests that the multifidi are not involved much in initiating movement but are instead muscles of stability. The longissimus thoracis pars lumborum and iliocostalis lumborum pars lumborum act to extend the lumbar spine and therefore resist flexor moments on the spine. 10 These muscles, and the multifidi, are postural muscles with a large portion of fatigue-resistant Type I muscle fibers. 11 Important Considerations for Low Back Pain One of the added benefits of maintaining a stable core through strengthening exercises can be prevention, or in some cases management, of low back pain (LBP). Statistics indicate that 50 70% of people will experience LBP at some point in their lives, and currently, 18% of Americans suffer from it. 12 Although the exercises recommended in this article are designed to aid in preventing or recovering from noncomplicated causes of LBP, they are not intended to replace the guided treatment of a physician. Loss of bowel or bladder function in addition to LBP (from cauda equina compression) or a progressive motor weakness is considered a medical emergency. Those experiencing signs of severe systemic disease or vascular difficulties should also be treated as emergency cases. The Role of Muscle Dysfunction in LBP Core-stabilization exercises should stress targeted muscles while avoiding pain exacerbation or placing unnecessary or compromising force on the structures of the spine. Exercises designed for endurance, as opposed to strength, seem most beneficial to LBP patients. 13 Decreased speed of contraction, inefficient cocontraction of stabilizers, and tonic muscle atrophy all seem to contribute to a lack of core stability and are associated with LBP. Paraspinal muscles are associated with decreased EMG activity in patients with chronic LBP. 14 The transversus abdominis has been shown to activate before limb movement in healthy individuals, but LBP is associated with delayed contraction of this muscle. 1 Multifidus muscle atrophy has been noted on the symptomatic side of those with LBP. 15 Although this atrophy does not recover spontaneously, it does respond well to exercise, which seems to aid in the recovery from and prevention of LBP. 5,16 Exercise Posture and LBP Certain exercises substantially load target muscles and, in the process, might unnecessarily load spinal joints. The rehabilitation professional supervising a strengthening program must be prudent and critically analyze an exercise to ensure that it does not potentially harm the patient. For instance, a very common exercise designed for targeting the erector spinae is the superman. This exercise requires the athlete to lie prone and then hyperextend the spine, thus lifting the upper torso and legs off of the floor. This applies a compressive force between 2,000 and 4,000 N to the lumbar spine. 17 Research has indicated that compressive loads as low as 500 N are damaging to the facet joints. 18 Thus, the superman exercise should be avoided; it clearly exceeds the amount of compression associated with facet damage. The neutral spine is perhaps the best position in which to engage in exercise. 6 In supine, a neutral spine has a slightly lordotic posture that enables the clinician to palpate lumbar spinous processes without being able to pass the hand completely underneath the back. 7 The neutral position should be pain free. 2 ATHLETIC THERAPY TODAY JULY

Basic Core Exercises This section presents a few exercises and activities that activate core musculature.

A few basic or beginner exercises include the hollowing, or draw-in, exercise; bracing; curl-up; side bridge; and bird-dog.

The contractions are held for 3 10 s. Bracing exercises isometrically work most abdominal and paraspinal muscles. 8 They require the athlete to brace against potential movement of the spine.

4 Basic Core Exercises This section presents a few exercises and activities that activate core musculature. These exercises are relatively safe to perform and can therefore serve as a good starting point. A few basic or beginner exercises include the hollowing, or draw-in, exercise; bracing; curl-up; side bridge; and bird-dog. 2,8,19 The hollowing, or draw-in, exercise activates the transverse abdominis (see Figure 1). 2,8 Essentially, the athlete attempts to pull the navel toward the spine, creating a hollowed abdomen. The contractions are held for 3 10 s. Bracing exercises isometrically work most abdominal and paraspinal muscles. 8 They require the athlete to brace against potential movement of the spine. Transverse abdominis and multifidi activity increase during this exercise, which is progressed by having the athlete maintain the brace during various arm and leg movements in supine. An example of abdominal bracing is the dead bug exercise (see Figure 2). Curl-ups, as opposed to sit-ups, require the lumbar spine to remain in contact with the surface on which they are performed. 19 The athlete performs curl-ups in supine with knee flexion while attempting to move the shoulder blades toward the knees, thus flexing the trunk throughout a relatively small range of motion. The athlete begins with the arms held across the waist, progressing to a fingers-interlaced position behind the head. It is important to avoid excessive cervical flexion during the curl-up, which is a natural predisposition. The cervical spine should remain in neutral or slight flexion throughout the movement. Side-bridging, or dynamic side support, activates the lateral spine flexors (Figure 3). 19 The athlete lies on his or her side, places the arm in contact with the surface at 90 of shoulder abduction to rest on the forearm and elbow, and then brings the trunk and hip off the surface to regain neutral alignment. Bird-dog exercises begin in quadruped and progress to three- and then two-point contact with the surface. 2 For example, the athlete begins on all fours in quadruped. The clinician can challenge the athlete in this position by using rhythmic stabilization perturbations. In a three-point bird-dog stance, one upper extremity leaves contact with the surface, whereas in two-point contact one upper extremity leaves the surface concomitantly with the contralateral lower extremity. 19 It is important to note that this exercise differs from the Figure 1 Hollowing exercise. The athlete attempts to pull the navel into the spine by flattening the abdomen and not just simply sucking in. Figure 2 Advanced bracing exercise known as the dead bug. Figure 3 Side-bridging exercise. superman because movement into extension occurs to neutral, not to hyperextension. Promoting Core Strength and Stability in Athletes Athletic rehabilitation typically includes advanced functional or sport-specific activities beyond the capacity of most healthy but nonathletic patients. The exercises 16 JULY 2005 ATHLETIC THERAPY TODAY

and activities in this section are designed for athletes in the return-to-sport phase of rehabilitation. These might also be appropriate conditioning activities for healthy athletes.

5 and activities in this section are designed for athletes in the return-to-sport phase of rehabilitation. These might also be appropriate conditioning activities for healthy athletes. In addition to strengthening during the return-to-sport phase, clinicians should promote local muscle endurance by increasing the duration of exercise. In addition, rotational activities should be included to address the necessary functional requirements of many sport activities (Figure 4). Balance activities are also important because trunk muscles play an integral part in maintaining posture. Activities that require active trunk flexion are especially useful in developing abdominal-muscle strength. The abdominal crunch or curl, previously discussed, can be progressed with various abdominal-exercise equipment on the market today. Research suggests, however, that traditional abdominal crunches are equal or superior to those performed with various types of exercise equipment. 20 It is perhaps best to progress trunk curls by increasing repetitions or resistance and then by changing the surface from stable to labile. Throwing and catching activities with a medicine ball are excellent for promoting core stabilization. This is mainly because concentric acceleration of the upper extremities during the throwing motion requires a stable base from which to produce force. Similarly, eccentric deceleration associated with catching requires the trunk to absorb and dissipate the force of the thrown object. Throwing and catching activities should both occur in the sagittal and transverse planes of trunk motion. Sagittal-plane activities include chest and overhead throwing activities, whereas transverseplane exercises involve rotational tossing and catching. The progression of these exercises involves combining the movements into multiple-plane activities such as diagonal patterns or sensory motor stimulation. Body-weight exercises such as push-ups, pull-ups, lunges, and single-leg squats or step-downs are also examples of activities that require dynamic trunk stability. A natural progression of body-weight activities occurs with increasing movement speed, which develops power. Plyometric exercises are the final progression for power development, both requiring and developing core stability. Activities that challenge one s dynamic balance require postural control of the trunk afforded by core stabilizers. Dynamic-balance activities perhaps best emphasize core stabilizers. These activities should begin on hard, stable surfaces and progress to softer, less stable surfaces. Examples include the single-leg stance with manual perturbation and performing activities without losing one s balance. Other functional-exercise regimens also promote core stabilization. A few such common organized exercise programs are yoga, Tai Chi, and Pilates. 2 The next article in this issue s theme presents Pilates as a means by which to develop core stability. Summary Core stability requires dynamic activation of the trunk muscles. Various activities are advocated for developing strength of the core muscles, but ultimately, the clinician should individualize a program to the athlete based on injury status and the specific rehabilitation phase. Furthermore, more evidence in the form of outcome-based studies is needed to truly ascertain the effectiveness of core-stabilization exercises in treating and preventing back pain. References Figure 4 Trunk rotation added into curl-ups during the advanced returnto-sport phase of rehabilitation. The athlete maintains isometric trunk flexion and then rotates side to side with or without resistance. 1. Hodges P, Richardson C. Inefficient muscular stabilization of the lumbar spine associated with low back pain: a motor control evaluation of transversus abdominis. Spine. 1996;21: Akuthota V, Nadler SF. Core strengthening. Arch Phys Med Rehabil. 2004;85(3 suppl 1):S86-S Panjabi MM. The stabilizing system of the spine. part II. neutral zone and instability hypothesis. J Spinal Disord. 1992;5(4): ; discussion Panjabi MM. The stabilizing system of the spine. part I. function, dysfunction, adaptation, and enhancement. J Spinal Disord. 1992;5(4): ; discussion Richardson C, Hodges P, Hides J. Therapeutic Exercise for Lumbopelvic Stabilization. 2nd ed. Edinburgh, UK: Churchill Livingstone; ATHLETIC THERAPY TODAY JULY

6 6. Yilmaz F, Yilmaz A, Merdol F, Parlar D, Sahin F, Kuran B. Efficacy of dynamic lumbar stabilization exercise in lumbar microdiscectomy. J Rehabil Med. 2003;35(4): Hall C. Therapeutic exercise for the lumbopelvic region. In: Thein Brody L, ed. Therapeutic Exercise: Moving Toward Function. Baltimore, Md: Lippincott Williams & Wilkins; 2005: Richardson CA, Snijders CJ, Hides JA, Damen L, Pas MS, Storm J. The relation between the transversus abdominis muscles, sacroiliac joint mechanics, and low back pain. Spine. 2002;27(4): Cholewicki J, McGill SM. Mechanical stability of the in vivo lumbar spine: implications for injury and chronic low back pain. Clin Biomech (Bristol, Avon). 1996;11(1): Wilke HJ, Wolf S, Claes LE, Arand M, Wiesend A. Stability increase of the lumbar spine with different muscle groups. a biomechanical in vitro study. Spine. 1995;20(2): Sirca A, Kostevc V. The fibre type composition of thoracic and lumbar paravertebral muscles in man. J Anat. 1985;141: Panjabi MM. Clinical spinal instability and low back pain. J Electromyogr Kinesiol. 2003;13(4): Taimela S, Kankaanpaa M, Luoto S. The effect of lumbar fatigue on the ability to sense a change in lumbar position. a controlled study. Spine. 1999;24(13): Cassisi JE, Robinson ME, O Conner P, MacMillan M. Trunk strength and lumbar paraspinal muscle activity during isometric exercise in chronic low-back pain patients and controls. Spine. 1993;18(2): Hides JA, Stokes MJ, Saide M, Jull GA, Cooper DH. Evidence of lumbar multifidus muscle wasting ipsilateral to symptoms in patients with acute/subacute low back pain. Spine. 1994;19(2): Hides JA, Richardson CA, Jull GA. Multifidus muscle recovery is not automatic after resolution of acute, first-episode low back pain. Spine. 1996;21(23): Callaghan JP, Gunning JL, McGill SM. The relationship between lumbar spine load and muscle activity during extensor exercises. Phys Ther. 1998;78(1): Dunlop RB, Adams MA, Hutton WC. Disc space narrowing and the lumbar facet joints. J Bone Joint Surg Br. 1984;66(5): McGill S. Low Back Disorders: Evidence-Based Prevention and Rehabilitation. Champaign, Ill: Human Kinetics; Hildenbrand K, Noble L. Abdominal muscle activity while performing trunk-flexion exercises using the ab roller, abslide, fitball, and conventionally performed trunk curls. J Athl Train. 2004;39(1): Barry Dale is an assistant professor in the Department of Physical Therapy at the University of South Alabama in Mobile. His teaching and research areas are related to exercise physiology, kinesiology, orthopedics, and neurology. Ryan Lawrence is a chiropractic physician practicing at Saraland Chiropractic in Saraland, AL. His primary clinical interest is in treating spinal disorders related to sports injuries. 18 JULY 2005 ATHLETIC THERAPY TODAY

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