RELATIONSHIPS BETWEEN ENERGY-EXPENDITURE AND POSITIVE AND NEGATIVE MECHANICAL WORK IN REPETITIVE LIFTING AND LOWERING

Determining the separate energy costs of the positive and negative mec hanical work in repetitive lifting or lowering is quite complex, as a mixture of both work components will always be involved in the up- and downward motion of the lifter's body mass. In the current study, a ne w method was tested in which coefficients specifically related to the positive and negative work were estimated by multiple regression on a data set of weight-lifting and weight-lowering tasks. The energy cost was obtained from oxygen uptake measurements. The slopes of the regres sion lines for energy cost and mechanical work were steeper for positi ve than for nega tive work. The cost related to the negative work was similar to 0.3-0.5 times the cost of the positive work. This finding i s well in line with data obtained directly from other isolated activit ies of either positive or negative work (e.g., ladder climbing vs. des cending). However, the intercept values of the regression lines were n ot significantly different from zero or were even negative. This was m ost likely due to the metabolic energy not related to processes that y ield mechanical work (e.g., isometric muscle actions) that was not con stant among trials.