Background: Shoulder injuries are highly prevalent among handball players due to the sport`s high-intensity and repetitive overhead movements, which place substantial mechanical demands on the shoulder joint. These injuries not only compromise performance but may also increase the risk of long-term musculoskeletal complications. Evaluating the isokinetic properties of the shoulder`s internal and external rotator muscles provides critical insights into muscle imbalances and can guide targeted preventive strategies. Objective: This study aimed to analyze and compare the isokinetic characteristics of shoulder internal and external rotator muscles during concentric contractions at ten angular velocities between amateur and professional handball players. Methods: Twenty-four handball players (12 amateurs and 12 professionals) participated in this cross-sectional comparative study. The mean age of the amateur group was 21.16 ± 1.11 years, and 21.66 ± 1.66 years for the professional group. Mean height was 1.82 ± 0.50 m for amateurs and 1.86 ± 0.58 m for professionals, while mean weight was 74.66 ± 5.86 kg and 82.83 ± 15.44 kg, respectively. Isokinetic data were collected at ten angular velocities using the Biodex System 3 Pro device. Key outcome measures included peak torque, time to peak torque, and muscle strength ratios. Results: Professional players demonstrated significantly higher peak torque at higher angular velocities (270°/s and 300°/s) compared to amateurs (p < 0.05). External rotator muscles exhibited significant differences across all velocities (p < 0.05), suggesting enhanced shoulder stabilization in professionals. Professionals reached peak torque faster, which may confer performance advantages but could marginally increase the risk of shoulder impingement. At higher velocities, internal rotators in professionals showed greater angles at peak torque (p < 0.05). Additionally, muscle strength ratios were more favorable in professional players at higher velocities (p < 0.05). Conclusions: High-velocity training is crucial for optimizing shoulder internal and external rotator muscle performance in handball players. Professional athletes displayed faster and stronger muscular responses, whereas amateurs exhibited delayed peak torque and weaker external rotators, with notable deviations from standard strength ratios. These findings highlight the importance of isokinetic assessment at multiple velocities to inform training interventions aimed at enhancing performance and minimizing injury risk in both amateur and professional handball players.
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