How do low/high height and weight variation affect upper limb movements during manual material handling of industrial boxes?

Abstract

Objectives: To evaluate the effect of surface height and load weight on upper limb movements and electromyographic (EMG) recordings during manual handling performed by both experienced and inexperienced lifter subjects. Methods: Sixteen experienced and sixteen inexperienced lifters handled a box (both 7 and 15 kg) from an intermediate height (waist level) to either a high or low surface.Electromyography and video images were recorded during the tasks. The 10 th , 50 th and 90 th percentiles were calculated for the deltoid and biceps muscles, shoulder flexion, shoulder abduction, and elbow flexion movements. Groups, right/left sides, weights and heights were compared. There were no differences between either groups or sides. Results: Weight and height variations affected EMG and posture, although weight had more impact on EMG. Shoulder abduction and flexion movements higher than 60° occurred, particularly for the higher surface. Shoulder flexion was also higher when the box was moved to the low height. This study provides new evidence as shoulder postures during boxes handling on low surfaces had not previously been evaluated. Conclusions: The high demand of upper limb in manual material handling tasks is clear, particularly for the shoulder. This knowledge can be used by physical therapists to plan better rehabilitation programs for manual material handling-related disorders, particularly focusing on return to work.Keywords: biomechanics; environment design; weight lifting; cumulative trauma disorders; physical therapy. ResumoObjetivos: Avaliar o efeito da altura de superfície e massa da carga nos movimentos e na atividade eletromiográfica (EMG) dos membros superiores durante o manuseio de carga realizado por sujeitos experientes e inexperientes. Métodos: Dezesseis sujeitos experientes e 16 inexperientes manusearam uma caixa (7 e 15 kg) de uma superfície com altura intermediária para uma superfície alta e/ou baixa. Durante as tarefas, foram registradas imagens de vídeo e EMG. Os dados foram processados para obtenção dos percentis 10, 50 e 90 referentes à EMG dos músculos deltoide e bíceps e aos movimentos de flexão e abdução do ombro e flexão do cotovelo. Foram comparados os grupos, lados (direito/esquerdo), massas e altura de manuseio. Resultados: Não foram encontradas diferenças significantes entre os grupos ou lados. As variações de massa e altura de manuseio afetaram a EMG e postura, embora a massa da caixa tenha tido mais impacto sobre a EMG. Os movimentos de abdução e flexão do ombro ocorreram acima de 60°, particularmente no manuseio para a superfície alta. A amplitude de flexão de ombro também foi alta quando a caixa foi movida para a superfície baixa. Esse resultado consiste em uma nova evidência, já que posturas do ombro durante o manuseio de carga em superfícies baixas não tinham sido investigadas. Conclusões: A alta demanda do membro superior em tarefas de manuseio de carga é clara, particularmente do ombro. Esse conhecimento pode ser usado por fisioterapeutas para um melhor planejamento da r...

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