The use of manual screwdrivers is still an important part of the work of, e. g., car mechanics or in the furniture section. Tightening or loosening screws often requires high torque strength. Therefore, the ergonomic design of the screwdriver handle helps to fulfill the working task by reducing physiological costs for the muscles of the upper extremity as well as complaints like blisters and pressure marks at the fingers and in the palm of the hand. In a series of screwdriver tests with 5 various handles (4 ergonomically designed and one "old-fashioned" handle as reference), bi-directional exertions with clean and oil-contaminated hands were demanded to simulate typical work tasks. Twelve male subjects (Ss), all right-handed, between the ages of 15 and 32, participated in standardized working tests during which the maximum achievable torque was determined. Simultaneously, electromyographic activities (EA) of 4 muscles involved in the working tasks were recorded, processed, and standardized. Significant differences between the standardized electromyographic activities of the muscles investigated were obtained depending on the direction of rotation. Also substantial differences between maximum torque strength were determined for pronation and supination, and for clean and contaminated contact surfaces.