Objective: This study aimed to conduct a usability evaluation of a rehabilitation service application for older adults and, based on the results, propose practical guidelines to improve application design. Specifically, the study sought to verify whether design improvements in content, graphics, layout, and interaction could enhance efficiency and user satisfaction.

Background: With the rapid growth of the aging population, rising healthcare costs, and reduced accessibility to medical services, interest in mobile health (mHealth) has significantly increased. Although various guidelines for designing applications for older adults have been proposed, few studies have empirically validated their effectiveness through experimental usability evaluations.

Method: A total of 36 older adults (mean age = 64.91, SD = 2.74) participated in experiments at the Senior Industry Innovation Center Living Lab. Participants were randomly assigned to use either the existing application (EA) or the improved application (IA), which incorporated seven guideline-based design improvements such as unified terminology, enlarged control buttons, optimized layout spacing, logical menu ordering, and audio/visual assistance. Three main tasks—rehabilitation exercise, gait assessment, and knee range of motion measurement—were evaluated. Usability was assessed through performance metrics (absolute/relative performance time, click count, error count) and the System Usability Scale (SUS).

Results: The IA demonstrated marked improvements compared to the EA. Relative performance times decreased by 59% (Task 1), 37% (Task 2), and 4% (Task 3). Relative click counts decreased by 88%, 92%, and 36% across the three tasks, while error counts dropped by 88%, 89%, and 50%, respectively. SUS scores also improved by 9% (Task 1), 13% (Task 2), and 10% (Task 3). Although absolute performance times and click counts increased in some cases due to additional preparation and help processes, these changes ultimately contributed to error reduction and improved user comprehension.

Conclusion & Application: The findings confirm that usability guidelines tailored for older adults can significantly improve the efficiency and satisfaction of mHealth applications. Particularly, unifying terminology, enlarging interface elements, and integrating supportive explanations were shown to reduce errors and enhance user confidence. This study provides empirical evidence supporting the application of design guidelines in developing mHealth services for older adults and offers practical insights for creating safer, more accessible, and user-friendly digital healthcare solutions.