This master’s thesis examines shoulder internal rotation force and how it is influenced by factors such as age, gender, handedness, occupation and arm-engaged sports activities. Shoulder problems are often complex due to the unique structure and mobility of the joint, and proper shoulder function is essential for performing daily activities and sports. A key aspect of this study is the use of the Ido-Isometer, an affordable and easy-to-use device for measuring internal rotation forces. Traditionally, shoulder force measurements require expensive equipment, often only available in specialized centers. The Ido-Isometer offers a feasible alternative, allowing force measurements to be conducted in broader clinical settings and even accessible for general practitioners. By providing insight into normal values for internal rotation forces across different demographic groups, this study contributes to improved clinical diagnosis and personalized rehabilitation for shoulder issues. This study also aims to establish reference values for internal rotation force for both men and women across different age categories. This approach offers an initial perspective to identify whether a patient may present with noticeable force loss. However, future studies will need to examine additional influencing factors such as body composition, a wider range of occupations, and larger sample sizes to achieve more accurate reference values. The findings of this study further emphasize the significant impact of demographic factors, such as age and gender, on shoulder internal rotation force. These insights can support the development of more tailored rehabilitation programs, such as addressing strength decline in older individuals or focusing on specific strength training for women. The findings have broad applications, from healthcare to sports injury prevention, and contribute to a wider understanding of the importance of shoulder force and preventive care for diverse target groups.