Core strengthening has become an area of increasing interest in fitness and rehabilitation circles because of the rising rate of exercise-related low back injuries. In fitness, we emphasise abdominal exercises to achieve a defined or toned stomach, but with little or any consideration of spinal stability. Yet, the core is a major stabilizer of the body and spine during movement.
Anatomy Of The Core
The abdominals are just one component that makes up our core. Additional structures that compose the core include the lumbar spine, back extensors, quadratus lumborum (side flexing muscle) and multi-joint muscles, namely, latissimus dorsi and psoas (primary hip flexor) that pass through the core, linking it to the pelvis, legs, shoulders, and arms.
If we consider the traditional approach to core strengthening, using a sit-up either on the floor or over gym ball, the repetitive movement here is spinal flexion. Evidence clearly shows that the damaging mechanism leading to disc herniation, or prolapse of the spine, is repeated lumbar flexion requiring only very modest concomitant compressive spinal loads. Therefore, sit-ups or curl-ups only serve to increase compressive forces on the spine replicating back injury mechanics.
In an effort to protect our back during exercise, we must consider the muscles that function to protect the spine. In particular, the transverse abdominis (TVA), a deep abdominal muscle, has received much attention with respect to spinal stability because of its orientation running horizontally around the abdomen. There are many trainers and therapists that advocate TVA activation to stabilize the spine, because research shows that together with the internal and external oblique the TVA increases intra-abdominal pressure when the abdomen is drawn inward or “hollowed,” therefore imparting functional stability of the lower back.
Abdominal Bracing Versus Hollowing
Instead, Dr. Stuart McGill, a leading spine biomechanist suggests that pulling or hollowing in the abdominals to “activate the transverse abdominis” to enhance spinal stability fails to actually stabilize the spine at all and that trainers who focus on this approach are misdirected. McGill (2009) found that abdominal hollowing and “drawing in” techniques reduces the potential energy of the spinal column causing the spine to fail at lower applied loads. An additional reason is that the TVA fails to target the major stabilizers of the spine like the quadratus lumborum that functions to laterally flex the back.
Maintaining a neutral or “stiff” spine during core training has been advocated as the safest and most effective approach to creating spinal stability. In contrast to TVA activation, McGill suggests that abdominal bracing enhances spinal stability. An abdominal brace occurs when there is simultaneous co-contraction of the abdominals, lower back, and buttock muscles. To perform abdominal bracing, the abdominal muscles are contracted (as if getting punched in the stomach) as well as the buttocks, which should generate simultaneous contraction of the lower back muscles. Another way to feel this contraction is to cough or simulate blowing out a candle.
Enhancing Spinal Stability
With an isometric abdominal brace, unlike drawing in the stomach or hollowing, all three layers of the abdominal wall (internal and external obliques and transverse abdominis) are co-activated with simultaneous activation of the latissimus dorsi, quadratus lumborum, and the back extensors. Therefore, the entire abdominal wall is activated from all directions as these muscle layers bind together to enhance spinal stiffness and stability.