Previous research findings demonstrated that there were interactions between the left and right limbs during physical activities but few of these studies examined the acceleration of arm movements. The purpose of this study was to examine the difference in the acceleration between bilateral and unilateral circular arm movements. Participants were 13 (six females and seven males) young college students who were right-handed without prior history of shoulder injury. An accelerometer was attached to the dorsal surface of the right hand for measuring acceleration. In addition, electrodes were placed at the anterior and posterior deltoids of the dominant (right) arm for recording electromyographic (EMG) activities. During the test, the subject stood on the force plate in a "walking" stance with the left foot as the leading foot. In doing the bilateral arm movement (B-ARM), the participants were required to swing the left arm for a half circle (180°) while the right arm swung a full circle (i.e., 360°) as rapidly as possible. All the arm movements were swung along the sagittal plane. The unilateral arm movement (U-ARM) was the same as the B-ARM, except that the left arm of the participant was not involved in any movement. The order of the arm movements was balanced across participants to attenuate sequence effects. Participants performed 10 trials on each of the B-ARM and U-ARM under two conditions: without carrying any weight (N-WT) and carrying a one-pound weight in each hand (W-WT). A three-way 2 × 2 × 2 (gender × arm movement × weight) repeated-measures ANOVA was used to examine the differences in the acceleration of arm movements between male and female participants. No significant (p > .05) interaction was found among the variables. Similarly, no significant (p > .05) main effect was found between gender or between N-WT and W-WT. However, significant (p < .05) main effect was found between B-ARM and U-ARM. The results indicated that B-ARM was consistent in achieving better acceleration across all the participants under different conditions. This also suggested interaction and facilitation between the left and right arms. The EMG activities demonstrated that the posterior deltoid was involved for a longer duration when performing the B-ARM and U-ARM. Results from the force plate indicated that participants achieved a better balance condition during B-ARM. The findings in this study provided important information in certain competitive sports that require both acceleration and strength, such as spiking in volleyball.Keyword(s): performance, physical activity