Partitioning the contributing role of biomechanical, psychosocial, and individual risk factors in the development of spine loads.

BACKGROUND CONTEXT The role of biomechanical workplace factors in spine loading has been well documented. However, our understanding of the role of psychosocial and individual factors in producing spine loads is poorly understood. Even less is understood about the relative contribution of these factors with respect to kinematic, kinetic and muscle activity responses, as well as spine loading. PURPOSE To explore the relative contribution of biomechanical and psychosocial workplace factors and individual characteristics on the biomechanical responses and spine loading. STUDY DESIGN/SETTING The contribution of various levels of workplace factors to spine loading was monitored under laboratory conditions. PATIENT SAMPLE Sixty (30 male and 30 female) college-age individuals who were asymptomatic to low back pain. OUTCOME MEASURES Trunk kinematics and kinetics, muscle activity and the three-dimensional spinal loads. METHODS The subjects performed lifting tasks while being exposed to varying levels of biomechanical (lift rate, load weight and task asymmetry) and psychosocial (social support and mental concentration) workplace factors as well as an unexplored (load placement) workplace factor. RESULTS The workplace job demands that had the largest contribution were load placement (4% to 30%) and load weight (15% to 55%). Mental concentration and social environment had a relatively small contribution to the spinal loads (up to 0.2%). Anthropometry played a large role in the shears (about 12% to 58%) but a relatively minor role in the compressive forces (about 3%). CONCLUSIONS Under the given experimental conditions, load weight is the most important factor when controlling compression forces associated with lifting, but other factors, such as individual characteristics, significantly contribute to the shear loads. Thus, one must account for the weight lifted and the anthropometric dimensions when designing the workplace. For the first time, the relative contribution of workplace job demands and individual factors in the development of spine loading have been identified.