Abstract
[Purpose] This study applied variable plank exercises on a stable surface consisting of a mat, on an unstable surface consisting of a dynamic cushion placed under the upper extremities and lower extremities. [Subjects] Forty-three healthy male and female subjects in their 20s voluntarily consented to participate in this study. [Methods] The subjects performed the plank exercises on the three support surfaces. Ultrasound imaging was conducted while they carried out plank exercises. [Results] The changes in the thicknesses of both the transversus abdominis and internal abdominal obliques were statistically more significant for LEDCP than for MatP. In addition, the changes in the thickness of the transversus abdominis were statistically more significant for LEDCP than for UEDCP. [Conclusion] Therefore, applying an unstable condition to the lower limbs using a dynamic cushion is considered more effective during plank exercises.