Muscle pain (myalgia) represents a large portion of work-related musculoskeletal disorders (WRMSD). The purpose of this study was to further examine the effects of cycle time, duty cycle, and load on the amount of rest taken by the muscles during a highly repetitive task. Ten female participants performed a simulated repetitive screw driving task with a T-handle grip against a vertical surface. Three torque levels (1, 1.75 & 2.5 Nm), 3 duty cycles (25, 50 & 75%) and 3 rest times per cycle (1, 2.5 & 5s) were tested in a full factorial design. The electromyographic signal (EMG) from 4 upper limb muscles of the right side were collected using standard electrode placements (flexor digitorum superficialis, extensor carpi radialis brevis, biceps brachii and trapezius). Results indicated that for muscles directly related to the task, the utilization of rest was positively dependent on the size of rest time given (p=3.5 x 10⁻² ECRB) and negatively related to the load (p=6.3 x 10⁻³ ECRB). The data suggests that increased load may not only increase loading of the muscle, but also decrease the amount of rest available to recuperate in high repetition tasks, both of which may increase the risk of muscle fatigue. When examining the load * duty cycle interaction of the Amplitude Probability Distribution Functions (APDF) at the static, median and peak levels, there was a fanning out effect of the data. At the static level, the 3 loads separated at the 75% duty cycle only (p=3.3 x 10⁻²). At the median level, the 3 loads separated at the 50% & 75% duty cycle (p<1.0 x 10⁻⁵). Whereas at the peak level, the 3 loads separated across all 3 duty cycles (with the high load always at the greatest MVC) (p<1.0 x 10⁻⁵). This confirmed that the APDF is sensitive to load of task and that the APDF has the potential to pick up increased activity time of muscles over that dictated by the task. The participant's discomfort increased as the load level increased (p=5.5 x 10⁻³). This increased discomfort with increased load may develop into pain and/or WRMSD if this task is continued over a prolonged period of time. The results suggest that rest must be given in a large enough block to be optimally utilized for the load and duty cycle requirements of a task.