This study aims to compare the thickness of the external oblique, internal oblique, and transverse abdominis during various plank exercise maneuvers. These involve applying pressure on a surface, and the types include plank exercise on a stable surface (SSP), plank exercise on an unstable surface (USP), and plank exercise with maximum expiration (MEP). The thickness was measured using ultrasound equipment while in the relaxed hook-lying position, to examine whether there were changes, change variances, and relative contribution ratios. Accordingly, this study recommends effective plank exercise maneuvers to selectively strengthen the abdominal muscles, in case there is a difference in changes, change variances, and relative contribution ratios in the thickness of the external oblique, internal oblique, and transverse abdominis.
A total of 30 healthy male subjects, in their 20s and 30s, voluntarily consented to participate in this study. Each subject lay relaxed in the hook-lying position, and ultrasound equipment was used to identify the thickness of the external oblique, internal oblique, and transverse at the test before beginning with the plank exercise maneuvers. At the end of the third expiration after measurement initiation, ultrasound imaging was performed. Subsequently, ultrasound imaging was done while the participants performed the plank exercise maneuvers, including SSP, USP, and MEP. The results were analyzed using paired t-test to compare the thickness of the external oblique, internal oblique, and transverse abdominis in relaxed state and during plank exercise maneuvers. Furthermore, repeated analysis of variance, i.e., ANOVA, was employed to compare change variances in the thickness of the external oblique, internal oblique, and transverse abdominis while performing the plank exercise maneuvers. The significance level for the statistical test was set at α=.05.
The study results revealed that the plank exercise maneuvers significantly increased the thickness of the external oblique in MEP (p<.05) and the internal oblique and transverse abdominis in SSP, USP, and MEP (p<.05) except for the external oblique in SSP and USP (p>.05). Change variances in the thickness of the external oblique slightly increased in all of the plank exercise maneuvers, especially in MEP, but there was no statistically significant difference (p>.05). In the case of the internal oblique, there was a statistically significant increase in USP and MEP (p<.05) as compared to SSP. Additionally, change variances in the thickness of the internal oblique in MEP increased more than USP, but there was no statistically significant difference between USP and MEP (p>.05). Change variances in the thickness of the transverse abdominis (p<.05) were statistically significant in MEP as compared to SSP and USP. However, there was no statistically significant difference between SSP and USP (p>.05). The relative contribution rate among abdominal muscles was not statistically significant when performing SSP (p>.05). The relative contribution rate was statistically significant between the external oblique and internal oblique when performing USP (p<.05). The relative contribution rate among abdominal muscles was statistically significant between the external oblique and internal oblique, external oblique and transverse abdominis, and the internal oblique and transverse abdominis when performing MEP (p<.05).
This study revealed that SSP, USP, and MEP increase the thickness of the external oblique, internal oblique, and transverse abdominis. The change variances of the internal oblique in USP, in particular, were statistically significant due to the activation of the internal oblique (p<.05). Furthermore, MEP activates the internal oblique and transverse abdominis that change variances of the internal oblique and transverse abdominis were statistically significant (p<.05). The relative contribution rate of transverse abdominis was the highest in MEP, and the relative contribution rate of the internal oblique was the highest in USP.
Therefore, MEP could be considered a lumbar stabilization exercise when selective activation of the transverse abdominis is required, whereas USP could be considered an exercise for lumbar stabilization when selective activation of the internal oblique is needed.