Introduction: The spinal loads depend on moment arm of the object, and regardless of the lifting technique, it can be effective in reducing the risk of low back pain. However, thoracic kyphosis variations during lifting can affect the moment arm of the external load.Materials and Methods: In this study 12 men volunteers recruited for lifting a box with tow techniques (squat and stoop), three instructions (increased, decreased, and normal thoracic kyphosis), and two masses (10% and 20% of body mass). We used motion analysis system for calculation of the transverse distance between a box and fifth lumbar vertebral.Results: Lifting techniques (P < 0.001), kyphosis instructions (P = 0.039), and box masses (P = 0.001) had significant effects on the moment arm of external load. The interaction between lifting techniques and kyphosis instructions (P = 0.012), lifting techniques and box masses (P = 0.026), kyphosis instructions and box masses (P = 0.029), and finally between all three factors (P = 0.006) were also significant.Conclusion: Lifting technique and mass of the external load influenced moment arm. Using squat technique was associated with an increase in the length of the moment arm, but in general, the increase in the mass of the box, and thoracic kyphosis in squat technique make it reduce.