Handball and water polo are complex sports of a dynamic character that require good physical abilities, including strength. The ability of an athlete to increase the amount of displacement of a body, on which he acts by some force, very often enables him to achieve enviable sports results. In addition, it is important to perform this work in the shortest possible time intervals. That ability is expressed by a physical quantity called strength. Strength is one of the most important motor skills in sports, its training and development strengthens the locomotor system, improves working conditions, and at the same time achieves speed and endurance, which are also extremely important for achieving better results. The main goal of the research is to compare the muscle strength of the biceps brachii on several levels, ie between water polo players and handball players, their playing positions and before and after sports activities. The study involved 26 male respondents, mean age 21.77 years. The respondents are professional, senior athletes from the Zamet Handball Club and the Primorje Erste Bank Water Polo Club. The research was conducted in April 2021 in the Zamet Sports Hall and at the Kantrida Pools. A microFET®2 dynamometer, a device from Hoggan Scientific, LLC, United States, was used as a measuring instrument for testing. The results showed a statistically significant difference in the strength of the biceps brachii muscle of handball players and water polo players, and also regarding to training time. The handball players achieved better results in muscle strength both before and after training, while both groups showed better results in muscle strength after training, from which it can be concluded that training has a positive effect on increasing muscle strength. There is no statistically significant difference in strength between playing positions, which means that the position in which a particular player plays does not affect his strength, but his strength can affect the position in which he will play. In order to confirm the results of this research, additional more extensive research is needed with a larger number of respondents and a longer follow-up time.