Dynamometric assessment of shoulder external and internal rotators in young tennis players

The musculoskeletal profiles of tennis players have been the subject of a number of studies analyzing the range of motion and muscle strength, as well as the unilateral dominance of the upper limb muscles, which leads to a serious imbalance in the shoulder joint. Objectives: To evaluate the dynamometric parameters of the external rotators (ER) and internal rotators (IR) of the shoulder joint and to generate a detailed analysis of the normalized peak torque, power, endurance and strength asymmetry characteristics, as well as time-based characteristics for the purposes of enhancing the training process. Materials and Methods: Two elite adolescent tennis players from a professional tennis school were studied. Anthropometric characteristics were measured by impedance analysis, including segmental analysis. Isokinetic dynamometry of ER and IR was performed in isometric mode at angular positions (°): 60, 40, 20, 0, -20, -40 and in concentric mode at angular velocities of 180 °/s. Results: The anthropometric assessments indicated that both athletes exhibited normal body composition. However, segmental analysis revealed that the dominant arm (DA) had a higher muscle mass compared to the non-dominant arm (NDA), which exhibited greater fat accumulation. These findings were supported by bilateral asymmetry data, demonstrating very high asymmetry values for ER between the DA and NDA, ranging from 25% to 52%, and high asymmetry values for IR, ranging from 15% to 27.5% in both athletes. Tennis Player 1 exhibited a unilateral asymmetry of 87.9%, significantly exceeding the normative range of 66-70% for both the DA and NDA, and reduction in acceleration time. In contrast, Tennis Player 2 did not exhibit such imbalance in the DA and the time-based parameters indicated rapid acceleration, high work capacity, and power output. These results could be associated with both prolonged training experience and potentially with hereditary factors determining the athlete's type of nervous system. Conclusion: The findings of this study highlight the benefit of assessing ER and IR strength in tennis players. The study indicates that when assessing ER and IR of the shoulder joint, the parameters with significant informative value for optimizing the training process include the coefficients of unilateral and bilateral asymmetry, acceleration time, time to peak torque, and maximal work per kilogram of body weight. Evidence has been provided for: (1) the necessity of developing strength in the internal and external rotators of the NDA; and (2) a probable relationship between the capacity for rapid acceleration and explosive strength generation of the shoulder external and internal rotators, and the hereditary determination of the athlete's nervous system type. These findings underscore the need for individualized testing and training approaches to mitigate muscular imbalances and enhance athletic performance.