| Popis: |
Dynamic pushing activities are very common in industry and are significantly represented in accidents; however, these activities have seldom been the subject of biomechanical investigations. Six male subjects, not experienced with the task, were evaluated for muscular moments and mechanical work at all body joints and also for spinal loadings at the lumbo-sacral joint (L5/S1). The data were recorded in synchronization using cinematography and force platforms. Dynamic segmental analyses were performed to calculate net moments at each joint. A model using two single equivalent muscles, either the flexor or the extensor of the back, was used to estimate internal loads at L5/S1. Joint muscular work was calculated from the integration of muscular power. Three treatments were administered which included pushing a 22.0 kg box onto shelves of different heights, that is low (58 cm), medium (99 cm) and high (141 cm), approximately corresponding to knee, hip and shoulder levels. Analyses of variance with repeated measures were conducted and the locations of significant differences were made with Scheffe method of multiple comparisons. The results showed that the working height is an important factor with the upper limbs predominantly involved at all pushing heights but considerably more at the higher level. The lower position is more demanding for the back and requires larger amounts of energy. The center position appears optimal. Conflictual results about the participation of the lower limbs were encountered by using two different methods of analysis which emphasize the limitation of the work-energy approch for assessing isometric exertions. It is recommended that a biomechanical analysis of working tasks include the integral evaluation of all body joints and all factors of human performance. |
