Effects of Forearm Support on the Mechanical Properties of Forearm and Shoulder Muscles During Typing Task

Purpose: This study examined the effects of the forearm and wrist support on the mechanical properties of shoulder and forearm muscles during a typing task using myotonometric assessment.Given that prolonged typing is associated with increased shoulder loading and work-related musculoskeletal disorders, understanding the mechanical muscle responses to different support conditions may provide clinically relevant ergonomic evidence.Methods: Twenty-eight healthy adults in their 20s participated in this study.Muscle mechanical properties were measured using the MyotonPRO device under two typing conditions: forearm support and wrist support.The muscle tone and stiffness of the upper trapezius, anterior deltoid, middle deltoid, posterior deltoid, and extensor carpi radialis longus were assessed on the dominant side.Paired ttests were conducted to compare the differences between the two support conditions.The significance level was set at p< 0.05.Results: The anterior deltoid showed significantly lower muscle tone under the forearm support condition (21.88 ± 3.83 Hz) compared to the wrist support condition (22.85 ± 4.02 Hz) (p< 0.05).Similarly, muscle stiffness of the anterior deltoid was significantly lower with forearm support (496.55± 137.25 N/m) than with wrist support (525.23± 132.81 N/m) (p< 0.05).Conclusion: Providing forearm support during typing reduces the anterior deltoid muscle tone and stiffness compared to wrist support alone.These findings suggest that adequate forearm support may decrease the shoulder muscle loading during repetitive computerbased tasks.