The Monday Memo
January 29, 2018 PITT DPT STUDENTS
Hollowing vs. Bracing: Building the Proper Foundation for Spine Stability
Abdominal hollowing and abdominal bracing are two techniques commonly used in the outpatient physical therapy setting to treat both acute and chronic low back pain patients whose symptoms are a result of some degree of spinal instability, or an inability to use their musculature properly to maintain their spine within the “neutral zone.” The mutual goal of these exercises is to teach the patient to reactivate certain muscles of their core with the purpose of increasing stiffness of the spine, enabling it to more effectively withstand potentially compromising loads and positions that can result in further pain and injury. Though both exercises are used to treat the same activation deficits of the spinal stabilization musculature, recent evidence has emerged calling into question the effectiveness of the abdominal hollowing technique in achieving this goal, and even suggests a potentially deleterious effect of the exercise in certain scenarios.
The abdominal hollowing exercise, which involves a selective drawing in of the transversus abdominis (TA) muscle to create a “hollowing out” effect in the abdominal region, gained in initial popularity due to evidence that found delayed and diminished EMG activity of the TA in certain patients with low back pain. This research failed, however, to examine the other surrounding musculature of the core, and more recent evidence has found that similar activation deficits were found in additional muscles of the abdominal cavity, suggesting that this delayed and diminished muscle activation is not unique to the TA, but rather pervades the surrounding deep abdominal musculature in certain low back pain patients. Abdominal bracing; which involves a submaximal co-contraction of these affected muscles such as the internal and external obliques, quadratus lumborum, rectus abdominus, transversus abdominis, lattisimus dorsi, and erector spinae, among others; might potentially be better suited to address the widespread activation deficits seen in these patients.
Additional research that examined the forces on the spine under varying loads and positions concluded that holding an isometric TA contraction decreased the potential energy of the spine and caused it to fail at lower loads. This evidence runs contrary to the belief that this isolated contraction increases spinal stability and refutes the clinical reasoning behind maintaining this type of contraction during various exercises such as squats. This reasoning was further called into question by a study that compared a stabilization exercise program involving isometric TA holds in conjunction with various exercises such as bridges and bird dogs with a similar program encouraging participants to employ their natural spinal stabilizing mechanisms throughout their exercises. The trial found that there were similar improvements between groups on pain outcomes, but the general, non-hollowing exercise group had greater improvements in self-reported disability scores. The study suggests that encouraging the body to employ its natural stabilizing mechanism by synchronously activating its abdominal cavity musculature may be more effective than isolating specific core muscles at achieving spinal stability.
Synchronous contraction of muscles about a joint increases the stiffness of that joint more effectively than contraction of a single muscle crossing the same joint. This principle is especially important when attempting to increase stiffness and ultimately stability of the spine and can be achieved by training the totality of the core musculature to synchronously contract with the abdominal bracing exercise to ultimately enable the patient to maintain this stiffness throughout their daily activities. An appropriate level of stiffness required for safe performance of most non-athletic activities only requires the core muscles to contract at 25% of their maximum voluntary contraction level. The principle of stiffness can and should be extrapolated to high level athletes as well in order to optimize safe and effective performance. A powerlifter, for example, must maintain a very high degree of co-contraction during a squat or deadlift in order to keep his or her spine in a neutral position when under heavy loads. This minimizes the risk for injury to the spine and maximizes performance by providing a solid foundation upon which the more distal joints can operate. Rapid contraction and relaxation of the abdominal brace is also important for athletes requiring more ballistic bursts of speed, such as baseball pitchers, golfers, mixed martial artists, and hockey players. It is essential for these athletes to be able to adequately activate their core musculature synchronously in order to accomplish the explosive movements required by their sports. A mastery of the abdominal brace technique may be particularly useful for returning these patients to their previous level of sport participation and skill.
To optimally teach safe and effective movement to our patients, we must replicate in the clinic those motor patterns that are demanded for performance in the real-world setting. This involves synchronous and synergistic activation of all muscles responsible for accomplishing a task, not isolated activity of muscles such as the transversus abdominis, which, when selectively contracted, has been shown to decrease potential energy and load tolerance of the spine. The healthy body activates its core muscles synchronously to prepare for and withstand movement and load on the spine. It is important to encourage that synchrony with the bracing technique to achieve optimal spine stability and performance.
-Brooks Kenderdine, SPT Class of 2019
McGill, S., PhD. (2010). Core Training: Evidence Translating to Better Performance and Injury Prevention(Vol. 32, Rep. No. 3). Lippencott Williams & Wilkins.
McGill, S. (2017). Ultimate back fitness and performance. Gravenhurst, Ontario: Backfitpro Inc.