Developing norms for manual carrying tasks using mechanical efficiency as the optimization criterion.

The primary objective of this investigation was to determine optimum activity levels when carrying symmetrical loads in front of the body. Efficiency of mechanical work was used as the response variable for optimization purposes. This was defined as the ratio between the rate of energy transfer between and within body segments (Wwb) and the rate of net metabolic energy expenditure during the task (RNME). Response surface methodology was used to develop a model describing the relationship between the efficiency of mechanical work and three task related variables, i.e., load handled, frequency of handling and carrying distance. It was determined that a maximum efficiency of 31.74% is achieved under a combination of task conditions as follows: load = 16.72 kg; frequency = 3.64 handlings/min and carrying distance = 10.61 m. The implications of these findings are discussed in the paper.