||Optimism is considered a relevant parameter in sport performance and this study aims to analyse its effects in adverse circumstances. In this study, 66 swimmers (boys and girls) with an average age of 13. 66 completed the same test at two different times. After the first test, they received negative feedback (a higher than real time) in order to check the effects on the second test. The results of this study were expected to replicate the study published by Seligman at Berkeley University in 1990. Interestingly, after such negative feedback, pessimists showed significant differences between the first and second tests. In contrast, although not statistically significant, our results indicate that all the swimmers whose performance improved in the second test had optimistic profiles. Finally, we discuss the use of evaluating and providing training in optimism for enhanced performance in competitive sports.