Background: A kinetic chain approach to shoulder rehabilitation is recommended. This study aimed to compare muscle activity between the isolated external rotation exercise and an exercise incorporating a kinetic chain approach in adults with shoulder pain. It also sought to identify muscle activation differences with the same tasks between asymptomatic adults and those experiencing shoulder pain. Methods: This is a randomized crossover trial. Twenty-four adults participated; 12 with shoulder pain and 12 without. Both groups performed isolated external rotation and kinetic chain exercises, with the sequence randomly allocated. Shoulder and scapular muscles were measured using surface electromyography. Mixed-effects models were used for the main statistical analysis. Results: Significant changes in muscle activation levels were observed with the kinetic chain strategy compared to isolated resistance exercise. In the exercise factor, a significant decrease of 8.9% was observed in the maximum activation of the infraspinatus muscle with kinetic chain implementation. Conversely, the latissimus dorsi muscle showed a significant increase of 16.5% in maximal activation with kinetic chain compared to external rotation exercise. Conclusion: Implementing the kinetic chain approach led to significant changes in muscle activation. It offers potential benefits for shoulder rehabilitation, making it an alternative to isolated external rotation exercises.