Intra-Abdominal Pressure With Low Back Pain
In the early 1990’s, a number of researchers looked at the role and activation patterns of the trunk muscles as they related to the concept of spinal stability. In Sweden, Cresswell et al. reported a series of studies indicating that intra-abdominal pressure was increased during functional tasks. Specifically the activation of the TrA was correlated with this:
- Fine-wire electrodes were used to assess TrA, internal oblique (IO), external oblique (EO) and rectus abdominis (RA) activity while intra-abdominal pressure was measured through the stomach. Does not sound like a fun test, does it? The TrA muscle activity was most consistently related to changes in intra-abdominal pressure.
- Unexpected and expected, self-induced perturbations were delivered to the trunk by suddenly loading a vest strapped to the torso of six male subjects. Again, also in this study the TrA was always the first muscle active in both conditions.
During isometric trunk flexion, IAPs were increased with accompanying high levels of activity from the abdominal muscles. In contrast, little activity from those muscles occurred during isometric trunk extension, although levels of IAP were similar. When adding valsalva with isometric trunk extension, activity from EO and IO was reduced while IAPs remained fairly constant.
These studies suggest that increase in IAP is a mechanism designed to improve the stability of the trunk through a stiffening of the whole segment. Activation of muscles such as the diaphragm and TrA is suggested as helping provide control over the level of IAP during controlled trunk tasks.
- Observations on intra-abdominal pressure and patterns of abdominal intra-muscular activity in man.
- The influence of sudden perturbations on trunk muscle activity and intra-abdominal pressure while standing.
- The role of the abdominal musculature in the elevation of the intra-abdominal pressure during specified tasks.