Tasks associated with patient handling may present nursing aides with some risk of injuring the lumbar spine. The purpose of this study was to estimate the forces at L5/S1 and to assess mechanical work and energy transfers in a task consisting of raising a patient (a 72#xB7;6thinsp; kg manikin) from a chair using three different methods: (A) with the hands; (B) with the forearms behind the patient's back at shoulder level; and (C) with a belt held at waist level. Six male subjects took part in the experiment. Spinal forces were estimated from a static and planar mathematical model used in conjunction with cinematography techniques, a force platform and EMG recordings. External forces and the internal forces (compression and shear at L5/S1) were determined from free-body diagrams and static equations. The model was analysed for its sensitivity in estimating patterns of EMG forces, intra-discal and musculo-ligamentous forces, intra-abdominal pressure and inertial forces. The model was found to discriminate between the relative demands imposed on the spine by the different lifting methods, but the absolute values of the forces remain uncertain because of the uncertainty residing in many of the model's hypotheses. The method requiring a belt to lift the patient was found to be considerably more strenuous for the spine and also to require a larger amount of work; it should therefore not be recommended as a task for nursing aides.
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