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?
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.
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).
- 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.
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.
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- Inhalation position of the sternum and anterior-inferior chest wall
- Exhalation position of the sternum and anterior-inferior chest wall
- The abdominal brace
- Dying bug
- Dying bug with small hand weight
- Marching on foam roll with medicine ball in hands
- The overhead arm reach on a foam roll
- Medicine ball trunk twist