Spinal Stability: Abdominal Strengthening Versus Voiding

Stabilization exercise has become very popular in the treatment of low back pain (LBP). The goal of this type of exercise is to optimize muscle activation and coordination around the spine while minimizing the compressive load on the spinal tissues. Stabilization exercise in combination with modifications of daily activity has been shown to be effective in treating low back pain, although the exact mechanism of this benefit has not been clarified.

The central theme of the spine stability issue is the method by which patients activate their abdominal muscles and the proper progression of exercise for maximum benefit. Previous research by the Queensland Australia group (Hides, Richardson, Jull, etc.) showed that the transverse abdominis (TrA) is later recruited in patients with low back pain, leading to speculation that it was related to a spinal column. unstable or unhealthy. This also led to the development of a specific rehabilitation protocol involving attempts to exclusively activate and rehabilitate TrA, primarily using an abdominal emptying technique. However, most of the existing evidence to support this concept has been indirect or qualitative. In fact, it has been shown that TrA can only be isolated at very low levels of activation (maximum voluntary contraction of 1-2% or MVC).

At higher activation levels, such as during normal daily activities or athletic tasks, TrA has been shown to be an internal oblique (IO) synergist. In light of this, what the original TrA research suggested is that there is a deficit of motor control in patients with low back pain, not necessarily that TrA is the most important factor in this relationship. Subsequent research has shown that patients with low back pain have not only delayed TrA activation, but also other motor control deficits, including delays in other trunk muscles when the torso is moving rapidly, inhibited knee extensors, firing patterns of Buttocks disturbed when walking and inability to Breathe heavily and maintain spinal stability. This indicates an overall deficit in muscle coordination, rather than a specific deficit in one muscle.

As research on TrA emerged out of Australia, the University of Waterloo biomechanics laboratory (McGill and his PhD students, Grenier, etc.) developed an advanced and validated method for modeling the spine and calculating how muscles contribute to it. movement and stability of the spine. What has evolved from this work is support for abdominal strengthening as the optimal method to activate the spinal musculature. They also developed the “Big Three” exercises for spinal stability rehabilitation: curl-up, front plank / side bridge, and cross crawl. These exercises maximize muscle activity, while minimizing spinal compression.

It is important here to establish some definitions that apply to this study, and to this topic of rehabilitation in general:

• Spinal stability: the ability of the spinal column to survive an applied disturbance (known as Euler’s spinal stability). If the input energy (disturbance) is greater than the potential energy of the spine (stored in discs, ligaments, muscles and tendons), equilibrium will not be achieved.

• Abdominal Hollowing – Attempt to isolate the TrA by activating the lower abdominal wall while gently “retracting”.

• Abdominal orthosis: involves the activation of the abdominal muscles around the spine to a level that increases the rigidity of the torso.

This study, conducted at the University of Waterloo, aimed to determine which muscle activation strategy (abdominal cupping or abdominal strengthening) is most effective for stabilizing the lumbar spine. Eight healthy male subjects between the ages of 20 and 33 participated in this laboratory study, which used EMG data and simulated biomechanical models to measure spinal stability during four loading conditions, performed with two bracing and casting stabilization strategies. . The four loading conditions were:

1) without load in the hands (without lifting)

2) 10Kg in each hand (bilateral lift)

3) 10 kg only in the right hand and

4) 10Kg only on the left hand. EMG recordings were taken from surface electrodes placed on the following muscles: rectus abdominis, IO, EO, latissumus dorsi, thoracic erector spinae, lumbar erector spinae, and lumbar multifidus.

Since TrA and IO have been previously established as synergists, the IO log is presumed to represent TrA activity (this presumption has been previously validated). Both bracing and casting were performed with ultrasound image guidance according to previous studies. The kinematics of the column were measured and modeled using the Isotrak 3D imaging system. The main outcome measures used were spinal stability index and spinal compression (each calculated using laboratory modeling techniques using raw data).

Relevant results of this study include:

• Simulation and in vivo data indicated that abdominal bracing was superior to abdominal cupping in terms of increased spinal stability with lower compression.

• Reinforcement increased column stability an additional 32% compared to hollow, while only increasing compression by 15%

• In all subjects, selective activation of TrA was extremely difficult, if not impossible, as evidenced by the fact that all other abdominal muscles do not remain silent during abdominal emptying; this suggests that abdominal emptying appears to lead to some degree of reinforcement

• all simulations performed indicated that TrA had no effect on spinal stability

Conclusions and practical application:

The results of this study indicate that abdominal brace is a superior strategy to increase spinal stability and save spinal load compared to abdominal cupping. The authors were quick to point out that these results should not diminish the potential benefit of voiding to retrain a TrA deficiency from a motor control perspective, as it is still part of the abdominal wall. However, the common advice from exercise therapists and practitioners to “lure” in an effort to increase stability appears to be misguided. It may also be relevant that this study indicated that any attempt at cupping appeared to recruit other abdominal muscles and therefore represented a low-level corset. The authors speculate that during muscle activation, the layers of the abdominal wall may coalesce, resulting in increased stiffness of the spine. If this is true, the TrA would still be important as a member of the “muscle orchestra” rather than a solo collaborator.

Returning to the original finding of delayed TrA activation in patients with back pain, the authors of this study cleverly suggest that this finding may be “statistically significant, but not mechanically significant.” From a practical perspective, abdominal bracing is easier to achieve and appears to be a more effective strategy to implement with patients with low back pain. The exact role of TrA-specific training still needs to be studied further.

It should be noted that this was a small study, conducted in a small group of healthy subjects. More studies are required to quantify these relationships in older back pain patients and other patient populations.