Unstable surfaces have been suggested to be used in training trunk and core stability. However, the use of unstable surfaces in training has come under question lately with research suggesting lower levels of activation compared to stable surfaces (Behm et al., 2010). The instability requires additional muscle activation to maintain stability. Therapists sometimes prescribe exercises using unstable surfaces such as Thera-Band® Stability Trainers and Stability Discs for patients with low back pain.
Researchers measured trunk muscle activity, lumbar range of motion, and balance during 5 common lumbar stabilization exercises performed on stable and unstable surfaces using an inflatable disk: quadruped, side bridge, modified push-up, squat, and shoulder flexion.
They found that patients with low back pain had adaptive recruitment patterns while maintaining similar levels of balance and lumbar range of motion compared to healthy subjects. There was little increase in electromyographic (EMG) activation among low back pain patients between the stable and unstable surface, and some exercises actually increased lumbar range of motion on unstable surfaces, which is not desirable during lumbar stabilization exercise. Based on these findings, the researchers questioned the need and benefit for using labile surfaces in patients with low back pain.
It’s important to note that the researchers only investigated superficial abdominal and low back muscles. Unstable surfaces are thought to activate deeper stabilizing muscles, which is the reason clinicians use them when rehabilitating spine patients. It’s quite possible that deeper muscles were activated in this study because the lumbar spine was shown to move without increased activation of the superficial muscles. O’Sullivan and colleagues found similar results when evaluating muscle activity and lumbar movement on an exercise ball.
Based on the results of this study, clinicians need to provide an appropriate level of instability to ensure the lumbar spine remains stable during the exercise. The Thera-Band System of Progressive Balance Training allows clinicians to choose the appropriate amount of instability during progressive balance exercises similar to the color-coded progression of Thera-Band elastic resistance from low to high levels of instability: Green > Blue > Black > Silver.
REFERENCE: Desai I, Marshall PW. Acute effect of labile surfaces during core stability exercises in people with and without low back pain.
J Electromyogr Kinesiol. 2010 Dec;20(6):1155-62.