Effects of Surface Stability on Muscle Activation during Plank Exercise

This study aimed to compare rectus abdominis (RA) and anterior deltoid (AD) muscle activation during plank exercise performed on different unstable surfaces. Sixteen recreationally active males participated in this study. A ground surface was used as a stable surface (SS), whereas gymnastics rings (GR) and the Bosu ball (BB) were used as unstable surfaces. Under the dual instability (DI) condition, participants placed their feet in the GR and elbows on the BB. Participants performed plank exercise under four different conditions. Muscle activation was measured in the upper rectus abdominis (URA), lower rectus abdominis (LRA), and anterior deltoid (AD) muscles during plank exercise. One-way repeated-measures analysis of variance was used to statistically compare muscle activation among the conditions. The level of significance was set at p < 0.05. Analysis showed that URA muscle activity was significantly greater under the DI condition than under the SS and BB conditions. In addition, URA muscle activity was greater under the GR than the SS condition. LRA muscle activity was significantly greater under the DI condition compared to the other conditions. In contrast, AD muscle activity was greater under the SS than the DI condition. In conclusion, these findings indicated that RA muscle activation was greatest on the dual instability surface, while AD muscle activation was greatest on the stable surface. Dual instability plank exercise may be a better choice than single instability and stable surface plank exercise for URA and LRA activation.