Investigation of the contraction ratio of transversus abdominis and internal oblique muscles during lumbopelvic stability test

Background. The clinicians administer lumbopelvic stability test (LPST) to evaluate core stability of lumbar spine and TrA muscle function. While the reduced thickness and contraction ratio of the TrA was well documented among people with nonspecific low back pain (NSLBP), the direct morphological changes of TrA during the LPST had not been reported so far. Purpose. To determine and compare the contraction ratio of deep abdominal muscles (TrA and IO) during the 7 progressive stages of the LPST in healthy individuals. Methods. Thirty healthy volunteers (15 males and 15 females) aged 21.83 ± 0.46 years participated in an experimental study. The TrA and IO thickness was assessed by ultrasound imaging (USI) TOSHIBA, Famio8, SSA-530A) at the right side in mid axillary line between 12 ^th rib and iliac crease. Images were taken for 2 trials during each level of LPST (7 levels) as measured by the pressure biofeedback unit (PBU). The thickness of the TrA and IO muscles were measured by Image J program (Image J®, NIH, USA) and the contraction ratio was calculated. A one way repeated measure ANOVA with post hoc analysis using the Bonferroni test at p<0.05 was used to analyse the data. Results. The contraction ratio of TrA showed a decreasing trend as the LPST was progressed to the 7 levels. Post hoc analysis showed a significant reduction in the contraction ratio of the TrA muscle in the 7 ^th level of the LPST (F=14.53, p=0.001). However, the contraction ratio of IO remains unchanged during all the 7 levels of LPST. Conclusions. The TrA muscle responded by reduced contraction ratio across the 7 levels of the LPST as measured by the PBU and USI. Further studies are warranted to compare the adaptation of the TrA muscle across 7 levels of the LPST among patients with NSLBP.