[Purpose] This study was conducted to investigate the effects of the push-up plus while using a balance ball, a sling, and a sling with a pulley in a creeping position on an unstable floor. [Subjects and Methods] The subjects were divided into three groups of 15 members each who performed the different three type methods of push-up plus (with scapulae protruding) in a random order while in a creeping posture. The muscle activity of each group in the push-up plus posture was measured using electromyography, and the measurement values were compared among the groups using one-way analysis of variance (ANOVA). [Results] The intergroup comparison revealed that the activation of the pectoralis major muscle of the balance ball exercise group was significantly decreased. In this comparison, the activity ratio for the pectoralis major muscles of the balance ball exercise group significantly decreased, and the activity ratio of their serratus anterior muscles significantly increased. From the post analysis, the differences in the activity ratios of the pectoralis major and serratus anterior muscles for the balance ball exercise group were significant when compared with those of the other groups. [Conclusion] Among the three different exercise methods in unstable situations presented in this study, the push-up plus exercise in a creeping posture using the balance ball can be recommended for the selective strengthening of the serratus anterior muscle.