The effect of isometric contractions of upper and lower limb muscles on the ultrasonic thickness of the transversus abdominis muscle

Background: The transverse abdominis (TrA) muscle is one of the most important muscles that contribute to the stability of the lumbar spine. Strengthening of trunk muscles that have a significant role in trunk stability is very important in the field of professional sport, sport medicine and rehabilitation of patient with low back pain (LBP). Identifying the exercises that can improve the strength and endurance of these muscles in the efficient way is an important challenge in rehabilitation of LBP patients. The aim of this study was to investigate the effect of maximum voluntary isometric contraction of upper and lower limb muscles on ultrasonic thickness of the TrA muscle. Methods: This is a pre-test post-test study. Thirty healthy young male subjects with mean age of 23 years were recruited from the university staff and student population (non probability sample). Ultrasonic thickness of the right and left TrA muscle (as an indirect measure of muscle activity) was taken at rest and during maximum isometric contraction of six muscle groups: shoulder and hip flexor, extensor and abductor muscles. Mixed-model ANOVA with repeated measures design were used to analyze data. To further analyses post hoc comparisons were performed with paired t-tests adjusted with the Bonferroni method. The significance level was set at P<0.05. Results: The result showed that mean TrA thickness on right and left sides during maximum isometric contraction of the upper and lower limb muscles was significantly thicker than in resting position (P<0.001). The type of isometric contraction had a significant effect on the thickness of the TrA muscle on dominant side (P<0.05). As a result, the greatest change in the thickness of TrA muscle on dominant side was observed in hip isometric extension (P<0.05). There was a significant difference between the thickness of TrA during upper limb isometric contraction of dominant and non-dominant side (P<0.001). Conclusion: Isometric contraction of upper and lower limb muscles especially in hip extension can increase the ultrasonic thickness of the transversus abdominis muscle.