Low back pain (LBP) continues to represent the leading occupationally-related musculoskeletal disorder experienced by workers. Previous surveillance studies (Marras et al., 1993;1995) have indicated that the most robust individual marker of risk for occupationally-related LBP is load moment (load magnitude x distance from the spine). Even this crude measure is capable of out performing more computationally complex assessment tools such as the NIOSH lifting guide and revised equation (Marras et al, 1999). In addition, many biomechanical studies suggest that the load moment exposure represents a biologically plausible pathway for a low back injury mechanism. However, no studies have attempted to specifically define the association between a various components of load moment exposure and LBP risk. Thus, the objective of this study is to explore how exposure to various components of load moment (i.e. components of the duty cycle) relate to LBP risk. This goal will be accomplished by developing and analyzing a rich and diverse database where the magnitude of the moments as well as the temporal exposure vary. Two phases will be necessary to complete this goal. Phase I will use an existing database of 515 manufacturing jobs to help understand the relationship between load moment and exposure frequency. Statistical models will be constructed and tested to help understand which features of the temporal exposure to moment might provide sensitive measures. In addition, instrumentation will be developed to precisely monitor load moment exposure. The final component of Phase I will involve the recruitment of various distribution centers needed to create a prospective database (phase II). Phase II will employ the moment measurement instrumentation in an industrial study of materials handling. In this prospective study, 1200 participants will be monitored for clinically relevant indicators of LBP status at the beginning and the end of an 18-month exposure period. During the exposure period, components of the workplace will be monitored including precise load moment exposure, temporal aspects of exposure (e.g. duty cycle, cumulative exposure, etc.), load position, etc. Workers will be monitored over an 8-hour shift. Upon completion of the prospective observation period, injury reporting, changes in clinical back status, etc. will be evaluated as a function of the load moment and temporal exposure characteristics using statistical models. In addition, easily measured surrogate indicators of the most predictive model measures will be developed so that these findings can be used to assess risk with minimal equipment. Collectively this study will not only enhance our knowledge of how exposure to various aspects of load moment affects LBP risk but will also lead to applicable measures with both high sensitivity and specificity for control of risk in the workplace.