WORKING ON A MOVING SURFACE - A BIOMECHANICAL ANALYSIS OF MUSCULOSKELETAL LOAD DUE TO SHIP MOTIONS IN COMBINATION WITH WORK

Ship motions are recognized by fishermen as a cause of high musculo-sk eletal load. In the present study, the motions of a Swedish trawler at sea were registered over three degrees of freedom. Simultaneously, th e working postures of a fisherman on board were registered in the sagi ttal plane during five different working situations: (1) standing erec t in still conditions; (2) holding a load of 21 kg in still conditions ; (3) standing erect during motion of the ship; (4) standing during mo tion of the ship, holding a load of 21 kg; and (5) repeatedly lifting and lowering a 21 kg load during motion of the ship. All registrations were sampled using a computer where data were processed in a two-dime nsional, dynamic biomechanics model, developed for this particular pur pose. Vertical and horizontal forces as well as moments were calculate d for seven major joint systems of the body, as was compression at the L4/L5 vertebral level. In situation (3), ship motions were mainly cou nteracted by motions in the lower extremity and lumbar back, thus indu cing increased strain in these parts of the body; other parts of the b ody were little affected. Holding a load considerably increased the lo ad on most joints. Lifting the load further increased the musculo-skel etal strain and also increased the range of moments in each joint as w ell as the range of lumbar compression. Moment at the C7 vertebral lev el was relatively unaffected by ship motions and by handling external loads.