The variable of vertical distance used in the experiment was fixed at 20~80 cm. The variable of working frequency was also fixed at 2 times per minute.Other variables are horizontal distance of 35 cm & 55 cm and weight of 10 kg & 25 kg. Vertical distance and working frequency were fixed, because horizontal distance and weight turned out to be the most influential factors if NIOSH Lifting Equation in past experiment results (Yang[19]).