This study identifies the strongest occupational risk factors and risk factor interactions in the development of indicators associated with cumulative trauma disorders (CTD). Suggestions for minimizing the occurrence of indicators associated with onset of CTD are presented. Five Occupational risk factors and six risk factor interactions were evaluated to determine their contribution to accepted indicators of the onset of CTD, including exertion, discomfort, difficulty, and fatigue. Taguchi's level-analysis procedure was used to design a 16-trial hammering experiment and to analyze the results. From the hypothesized occupational risk factors, repetition was found to have the strongest effect on the values of the physiological and subjective indicators of the onset of CTD.