Despite the fact that athletes and physically active persons are generally more satisfied with their bodies than sedentary people, physical activity seems to exert both negative and positive influences on body image. The aim of this study was to investigate the effect of a single session of exercise in state body image modification. In particular, we observed if a single session of sport or fitness activity could have a positive influence on state body image, considered as an episodic, evaluative and affective perception of the own physical appearance. Results showed an increase of the mean state body image rate (assessed with the Body Image States Scales, BISS) after a one-hour session of sport or fitness activities in a sample of 295 individuals. Intensity and fun seemed to be key-factors in state body image enhancement. These findings could have significant implications in the treatment of BI disturbances and in their prevention.