This study examines the effects of Instagram fitspiration images on male viewers' work out intention by integrating the processes of social comparison and social cognitive theory. The results from 1428 Instagram users in Taiwan, with the directions of comparison (upward, lateral, and downward) manipulated, indicate that upward comparisons with attractive models would strengthen self-improvement motives related to working out. In addition, pleasant affective responses to the images and one's self-efficacy for working out were also significant predictors. However, model attractiveness revealed a negative, direct effect on work out intention, suggesting that a seemingly rewarding model behavior itself discourages viewer imitation. Implications are discussed to contribute the understanding about male audiences' reactions to the same-sex body images associated with physical training. The findings verifying both the psychological and behavioral impacts of social influence also help demonstrate a more comprehensive picture about promoting exercise as a positive outcome of fitspiration imagery exposure.