Lower back pain (LBP) is a condition that affects about 70-80% of people at some point in their lives.(1) It is associated with abnormal motor activity in core muscles, particularly the deep muscles of the local lumbopelvic region.(2) When functioning normally, these muscles, particularly the Transversus Abdominis (TrA), provide spinal stabilization without help from the larger global abdominal muscles.(3) In patients with LBP, evidence has shown that there is decreased contraction, reduced thickness, and delayed activation of the TrA and multifidus muscles during movements that require its support.(2) Consequently, one way of treating LBP involves exercises that teach patients to selectively activate their deep core muscles with the goal of improving spinal stabilization.(4)
One issue that clinicians and patients come across when using core activation exercises is that it is difficult to perceive whether there is isolated contraction of the muscles.(2) Therefore, there is a need for feedback mechanisms that can be used in clinical environments to help patients increase their local muscle activation while decreasing global muscle activity.(3) Pressure biofeedback units are a non-invasive method of indirectly measuring core muscle activity through detecting pressure fluctuations caused by muscle contraction. A PBU is composed of a non-elastic air bladder inflated to a pressure of 70 mmHg that is placed between the area of interest and the supporting surface. It provides live feedback to the user during exercise, and it can be used by physical therapists, exercise trainers, and even patients in their homes.(3)
A standard example of PBU tests is the abdominal drawing-in test, which has patients contract their abdomen in a prone position without moving their spine or pelvis. If a patient correctly performs this test, they should be able to reduce the pressure in the PBU by 6-10 mmHg, which indicates that they are contracting the TrA without activating other abdominal muscles. In one study, examiners using the criteria that an increase in pressure or decrease less than 6 mmHg indicated TrA dysfunction were able to correctly identify 90% of subjects as having a history of LBP.(3) Another study showed that there was good agreement between PBU-measured TrA dysfunction and delayed contraction as measured by fine wire electromyography (EMG).(3)
Tools such as fine wire EMG and ultrasound imaging have been used to identify isolated contraction of local spinal stabilization muscles. However, they are rarely applied to clinical settings, as they are invasive, costly, or require technical expertise to use.(5) Since PBUs are designed to be non-invasive, cost-effective, and easier to set up, they provide a useful option for biofeedback in a clinical environment. Despite some conflicting evidence on the ability of PBUs to accurately measure TrA activation during exercise, they have been shown to benefit patients by providing live visual feedback during exercises, helping them achieve neutral spine position, reduce pelvic rotation, or increase abdominal muscle activity.(1)(2)(5) This ability to receive corrective feedback on their muscle actions during rehabilitative exercises is crucial for LBP patients to get the most out of their treatment.
How do you use PBUs in your practice and what are some shortcomings that you think can be addressed?
- Noh, K., Kim, J., Kim, G., Ha, S., & Oh, J. (2014). The Influence of Dual Pressure Biofeedback Units on Pelvic Rotation and Abdominal Muscle Activity during the Active Straight Leg Raise in Women with Chronic Lower Back Pain. Journal of Physical Therapy Science, 26(5), 717-719. doi:10.1589/jpts.26.717
- Crasto, C. F., Montes, A. M., Carvalho, P., & Carral, J. M. (2019). Pressure biofeedback unit to assess and train lumbopelvic stability in supine individuals with chronic low back pain. Journal of Physical Therapy Science, 31(10), 755-759. doi:10.1589/jpts.31.755
- Richardson, C., Jull, G., & Hodges, P. (2007). Therapeutic exercise for spinal segmental stabilization in low back pain: Scientific basis and clinical approach. Edinburgh, UK: Churchill Livingstone.
- Lima, P. O., Oliveira, R. R., Filho, A. G., Raposo, M. C., Costa, L. O., & Laurentino, G. E. (2012). Concurrent validity of the pressure biofeedback unit and surface electromyography in measuring transversus abdominis muscle activity in patients with chronic nonspecific low back pain. Brazilian Journal of Physical Therapy, 16(5), 389-395. doi:10.1590/s1413-35552012005000038
- Grooms, D. R., Grindstaff, T. L., Croy, T., Hart, J. M., & Saliba, S. A. (2013). Clinimetric Analysis of Pressure Biofeedback and Transversus Abdominis Function in Individuals With Stabilization Classification Low Back Pain. Journal of Orthopaedic & Sports Physical Therapy, 43(3), 184-193. doi:10.2519/jospt.2013.4397