Based on the scientiยฎ c evidence in published literature about precipitation of musculoskeletal injuries in the workplace, four theories have been proposed to explain these aZictions. Central to all theories is the presupposition that all occupational musculoskeletal injuries are biomechanical in nature. Disruption of mechanical order of a biological system is dependent on the individual components and their mechanical properties. These common denominators will be causally aVected by the individual's genetic endowment, morphological characteristics and psychosocial makeup, and by the occupational biomechanical hazards. This phenomenon is explained by the Multivariate Interaction Theory. DiVerential Fatigue Theory accounts for unbalanced and asymmetric occupational activities creating diVerential fatigue and thereby a kinetic and kinematic imbalance resulting in injury precipitation. Cumulative Load Theory suggests a threshold range of load and repetition product beyond which injury precipitates, as all material substances have a ยฎ nite life. Finally, Overexertion Theory claims that exertion exceeding the tolerance limit precipitates occupational musculoskeletal injury. It is also suggested that while these theories may explain the immediate mechanism of precipitation of injuries, they all operate simultaneously and interact to modulate injuries to varying degrees in diVerent cases.