In the last years notices of Work Related Musculo-Skeletal Disorders are significantly increased, for a much widespread mechanism of disease and risk identification. About the last, the methods of assessment, even if in great number, are not universally recognized. This study reports the application of four methods (Check list OCRA, OREGE, Strain Index, ACGIH) to evaluate 12 work emplacements at a different biomechanical overload level. The comparison revealed variability between the methods in situations of middle risk, while the methods substantially gave similar results in situations without any risk or with high risk. Methods could not reveal every component of the risk in a reproducible and univocal way also when the risk assessment was accordant. It is necessary a following analytical evaluation of each risk factor contributing to define the sintetic index. In the complex of biomechanical risk factors these ones might not be considered able to define unequivocally "accettable" or "not accettable" components.