The authors note that the development of flexibility is one of the main directions for swimmers specializing in the sport method of butterfly swimming. With the participation of young swimmers, the development of flexibility was tested in six tests. The author conducts an analysis of scientific and methodological literature. Taking into account the results of a study of the initial indicators of flexibility in young swimmers, a methodology for the development of flexibility with the help of TRX loops was developed and tested, which included goals, tasks, principles, methods, organizational and methodological features, expected result. A special set of exercises for the shoulder girdle, spine column, and legs was also developed. The results of flexibility development using TRX loops obtained in the experimental group showed a positive effect on the performance in girls and boys.