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Core Training: The Dangers of What Our Patients Think They Know

Craig Liebenson

Introduction

Abdominal or “core” training is becoming more popular all the time.  Traditional sit-ups are still in vogue, but may in fact be dangerous for the back. Modern biomechanics verifies the importance of the abdominal wall, but suggests it is functional, coordinated action of the kinetic chain linkage system from pelvis to rib cage that is most crucial. Train is best when the entire orchestra is trained rather than isolating individual muscles. The diaphragm, pelvic floor, oblique abdominals, transverse abdominus, rectus abdominus, as well as the lumbar spine musculature should all participate in a well coordinated manner.

The dangers of the sit-up

The sit-up places high compressive load on the disc,  involving  3350 N of force (McGill 2006, 2007). According to McGill the safe limit for an acute-subacute low back pain patient is approximately 3000N. The sit-up usually involves a posterior pelvic tilt which unnecessarily elevates disc load (Hickey and Hukins 1980). It is frequently performed early in the morning, which is a time of great risk due to increased intra-discal pressure (Adams 1985).

Isolation vs Integration

Spine stability is greatly enhanced by co-contraction (or co-activation) of antagonistic trunk muscles (Cholewicki and McGill 1996). Co-contractions increase spinal compressive load, as much as 12%-18% or 440N, but they increase spinal stability even more by 36% – 64% or 2925N (Granata 2000).  They have been shown to occur during most daily activities (Marras 1990). This mechanism is present to such an extent that without co-contractions the spinal column is unstable even in upright postures! (Gardner-Morse 1998).

Poor motor control of the “core” muscles has been found to be correlated to back pain. Research at Yale University have shown that a specific motor control signature of delayed agonist-antagonistic muscle activation predicts which asymptomatic people will later develop low back pain (LBP) (Cholewicki 2005). What researchers found were longer muscle response latencies to perturbation in the “at risk” group than in healthy control subjects.

Inappropriate muscle activation patterns during seemingly trivial tasks (only 60 Newtons of force) such as bending over to pick up a pencil can compromise spine stability and potentiate buckling of the passive ligamentous restraints (Anderson 1990). Certain times of the day such as in the morning or after prolonged sitting  render the spine so unstable that if “surprised” by trivial load an injury can be precipitated (Adams 1995).

Paul Hodges and colleagues from Australia  have shown  that delayed activation of the transverse abdominus muscle during arm or leg movements distinguishes between LBP patients and asymptomatic individuals (Hodges 1998, 1999). However, according to Canadian scientists focusing on a single muscle is like focusing on a single guy wire (Kavcic 2004). Research in Pr. Stuart McGill’s laboratory at the University of Waterloo in Canada has found that the entire orchestra of muscles is responsible for spinal stability (Kavcic 2004). They demonstrated that different muscles played greater or lesser roles depending on the activity/exercise and that no single muscle can be considered ‘the stabilizer of the spine”.

How Should Functionl Core Training Occur?

Proper Breathing

If spine stability is compromised when one is gasping for air the natural result will be low back injury (e.g. a deconditioned person shoveling snow). McGill demonstrated a loss of control of the “neutral spine posture” during weight lifting under challenging aerobic circumstances (McGill 1995).

For all abdominal exercises it is important that the patient is cued to maintain normal respiration.

The Exhalation Position of the Rib Cage

Kolar (2007)  has recommended that to achieve stronger co-activation of abdominal wall the anterior rib cage should be depressed into a similar position as occurs with atctive exhalation. Raising the ribs up is synchronized with the inhalation phase of respiration and will inhibit the normal postural function of the diaghragm. It is noted that the thoraco-lumbar (T/L) junction is hyperlordotic and the diaphragm is oblique in this position (see figure 1). Ideally, a depressed (e.g. caudal) anterior chest position is facilitated which is the “exhalation” position. In this case the T/L junction is more neutral and the diaghragm is “centrated” in a horizontal position (see figure 2). The “exhalation” position is believed to be facilitory of the abdominal wall since active exhalation is produced by the abdominal muscles.

Fig1

Figure 1

Fig2

Figure 2

Bracing the Core

Co-contractions  have been shown to occur automatically in response to unexpected or sudden loading and to have a stabilizing effect (Lavender 1989, Marras 1987). Stokes (2000) has described how there are basically two mechanisms by which this co-activation occurs. One is a voluntary pre-contraction to stiffen the spinal column when faced with unexpected perturbations. The second is an  involuntary, reflex contraction of the muscles quick enough to prevent instability following either expected or unexpected perturbations (Cresswell 1994, Lavender 1989, Marras 1987, Stokes 2000, Wilder 1996).

Performing an abdominal brace (AB) is very simple. The patient should pretend they are about to be pushed or hit and they will “automatically’ brace.

Neutral Spine Posture

The ideal spine posture is the same as occurs when standing upright – neutral lumbar lordosis. Many patients perform a posterior pelvic tilt which actually places the lumbo-sacral spine in flexion and thus can potentially harm the disc via end-range loading in flexion. The “neutral zone is the inner region of a joint’s range of motion (ROM) where minimal resistance to motion is encountered” (Panjabi 1992). According to McGill (2006) “Because ligaments are not recruited when lordosis is preserved, nor is the disc bent, it appears that the annulus is at low risk for failure.”.

Training the Core

After breathing and bracing are trained with good lumbar spine posture during such exercises as dying bugs, bird-dog, curl-ups, and side bridges. The patient is ready to take on more rigorous challenges. One of the most common mechanisms of injury is lumbar torsion. Controlling lumbar torsion is thus helpful for those patients who play tennis, golf, hockey, baseball, soccer, and any other sport involving bending and twisting.

The “stir the pot” exercise is an excellent way to train control of lumbar rotation (Reynolds 2009)(figure 3).

figure3-ball

Figure 3

  • If you can perfrom forward plank with stability, progress to this exercise
  • Tighten your core to stiffen your trunk
  • Move the ball side to side & in circles by small movements from your shoulders
  • Progress by performing on your toes with legs straight.
  • Progress further by placing your toes on a Bosu.

Conclusion

Abdominal exercises are utilized for cosmetic and therapeutic purposes. There are a number of myths which should be unmasked about this subject regarding sit-ups, morning exercise, the posterior pelvic tilt, the transverse abdominus, exhaling with exertion, etc.. The 4 pillars of core training described in this article should be incorporated into all abdominal training. The dying bug is an excellent starting point to “groove” healthy motor patterns. This should be seen as a first step, but not an end in itself. Progressions to side support, quadruped, and most importantly upright (squat, lunge, push, and pull) positions is essential to ensure sufficient stability in the lumbar spine during participation in job demands, activities of daily living, as well as sports and recreational activities.

References:

Adams, M.A., Dolan, P. 1995. Recent advances in lumbar spine mechanics and their clinical significance, Clin Biomech 10: 3‑19.

Adams, M.A., Hutton, W.C. 1985. Gradual disc prolapse, Spine 10: 524‑531.

Andersson GBJ, Winters JM 1990. Role of muscle in postural tasks: spinal loading and postural stability. In Winters JM, Woo SL-Y (eds) Multiple Muscle Systems, Springer-Verlag, New York Ch 23 p 375-395.

Cholewicki J, Silfies SP, Shah RA, et al. 2005. Delayed trunk muscle reflex responses increase the risk of low back injuries. Spine. 30(23):2614-20

Cholewicki J, Panjabi MM, Khachatryan A 1997. Stabilizing function of the trunk flexor-extensor muscles around a neutral spine posture. Spine 22: 2207-2212.

Cholewicki, J., and McGill, S.M. 1996.  Mechanical stability of the in vivo lumbar spine:  Implications for injury and chronic low back pain, Clin Biomech 11(1):1-15.

Cresswell AG, Oddsson L, Thorstensson A 1994. The influence of sudden perturbations on trunk muscle activity and intraabdominal pressure while standing. Exp Brain Res 98:336–41.

Granata KP, Marras WS 2000. Cost-benefit of muscle cocontraction in protecting against spinal instability. Spine 25:1398-1404.

Hickey DS, Hukins DWL 1980. Relation between the structure of the annulus fibrosis and the function and failure of the intervertebral disc. Spine 5:106-116.

Hodges PW, Richardson CA 1998. Delayed postural contraction of the transverse abdominus associated with movement of the lower limb in people with low back pain. J Spinal Disord 11:46-56.

Hodges PW, Richardson CA 1999. Altered trunk muscle recruitment in people with low back pain with upper limb movements at different speeds. Arch Phys Med Rehabili 80:1005-1012.

Kavcic N. Grenier S, McGill SM 2004. Determining the stabilizing role of individual torso muscles during rehabilitation exercises. Spine 29:1254-1265.

Kolar P 2007. Facilitation of agonist-antagonist co-activation by reflex stimulation methods in Rehabilitation of the Spine: A Practitioner’s Manual, Liebenson C (ed). Lippincott/Williams and Wilkins, Philadelphia.

Lavender SA, Mirka GA, Schoenmarklin RW, Sommerich CM, Sudhakar LR, Marras WS 1989. The effects of preview and task symmetry on trunk muscle response to sudden loading. Human Factors 31: 101-115.

Liebenson C. Functional Stability Training in Rehabilitation of the Spine: A Practitioner’s Manual. Lippincott/Williams & Wilkins (2nd ed), Philadelphia 2007.

Marras WS, Mirka GA 1990. Muscle activities during asymmetric trunk angular accelerations. J Orthop Res 8:824-32.

Marras WS, Rangarajulu SL, Lavender SA 1987. Trunk loading and expectation. Ergonomics 30:551–62.

McGill SM 2007. Lumbar Spine Stability: Mechanism of Injury and Restabilization in Rehabilitation of the Spine: A Practitioner’s Manual, Liebenson C (ed). Lippincott/Williams and Wilkins, Philadelphia.

McGill SM 2006. Ultimate back fitness and performance (2nd edition).Wabunu .

McGill,S.M., Sharratt,M.T., Seguin,J.P. 1995. Loads on the spinal tissues during simultaneous lifting and ventilatory challenge, Ergonomics 38: 1772-1792.

Panjabi MM 1992. The stabilizing system of the spine. Part 1. Function, dysfunction, adaptation, and enhancement. J Spinal Disorders 5:383-389.

Reynolds G. NY TIMES JUNE 17, 2009 “Is Your Ab Workout Hurting Your Back?”

http://well.blogs.nytimes.com/2009/06/17/core-myths/

Stokes IAF, Gardner-Morse M, Henry SM, Badger GJ 2000. Decrease in Trunk Muscular Response to Perturbation With Preactivation of Lumbar Spinal Musculature. Spine 25:1957-1964.

Wilder DG, Aleksiev AR, Magnusson ML, Pope MH, Spratt KF, Goel VK 1996. Muscular response to sudden load. A tool to evaluate fatigue and rehabilitation. Spine 21:2628–39.

Figure Legend:

  1. Inhalation position of the sternum and anterior-inferior chest wall
  2. Exhalation position of the sternum and anterior-inferior chest wall
  3. The abdominal brace
  4. Dying bug
  5. Dying bug with small hand weight
  6. Marching on foam roll with medicine ball in hands
  7. The overhead arm reach on a foam roll
  8. Medicine ball trunk twist

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