Purpose The purpose of this study was to investigate the effect of the bridge exercise with a sling on the thickness of the transverse abdominis according to the position of the arm and suggest the most effective position of the arm during trunk stability exercise. Methods The participants of this study were 16 college students in Daejeon D University. The position of the arms during the bridge exercise was set in three types; pronated hands next to the pelvis position, crossed arms over the chest position, and clasped hand overhead position. We performed the nonparametic test using SPSS for 18.0(Win). We used the Wilcoxon signed rank test to compare the thickness of the transverse abdominis to prepost intervention and the Friedman’s test to compare the thickness of the transverse abdominis according to the position of the arm. The statistical significance was set at p<0.05. Results After the intervention, when we compared the thickness of the transverse abdominis at the three types of arm position during the bridge exercise using the sling, a significant increase from 3.875±0.97 in pretest to 5.443±1.39(p<0.05) in the crossed arms position and 4.987±1.49(p<0.05) in the clasped hand overhead. However, there was no significant increase, only 4.550±1.04(p<0.05) in the position of the pronation hand next to the pelvis. Conclusion As a result of this study, the crossed arms posture above the chest in the bridge exercise using a sling was the most effective posture increases the thickness of the transverse abdominis.