Purpose:
The aims of the study were to determine the relationship between the shoulder muscles strength and the athletic performance of high-level swimmers and to detect the strength variables that had the biggest impact on high performance in sports swimming.

Methods:
The study involved 39 high qualified swimmers (12 females and 27 males). To determine the strength variables, shoulder flexion and extension were carried out in isokinetic conditions. A Biodex S4 dynamometer was used. The following protocols were applied: (1) 3 repetitions, 60°/s; (2) 20 repetitions, 180°/s. The r-Pearson correlation analysis or the rho-Spearman correlation analysis were used. The family-wise error was checked.

Results:
The level of strength had a greater influence on the swimming performance in males (25 of the 68 obtained variables) than in females (18 of the 68 variables). The strength variables that had the biggest impact on high performance in sports swimming were peak torque (r: 0.39–0.633), total work (r: 0.408–0.692), average power (r: 0.44–0.739), and average peak torque (r: 0.456–0.72).

Conclusions:
Regardless of the respondents’ gender or the analysed shoulder movement, the following variables were repeated: peak torque, total work, average power, and average peak torque. Unfortunately, the results were not statistically significant. Only acceleration time of the left shoulder in the arm flexion movement in males was significant. Despite this, once the muscular groups are similar for the listed strength variables, the swimmer’s capability to produce force out of water seems to help them perform better in the water.