During a lifting task the movement of the trunk can account for the majority of the external moment about the ankle. Though the angle of trunk flexion and the external moment about the ankles are roughly correlated, this correlation can be reduced by various segmental dynamics and momentums with the upper/lower extremities. Two methods are proposed in this technical note for describing the relationship between the kinematics and the kinetics of a lifting motion. The first relies on the phase plane analysis technique and explores the relative phase angle between the kinematic characteristics of lifting motion (i.e., trunk motion in the sagittal plane) and the kinetic characteristics of lifting motion (i.e., the net external moment). The second technique employs the moving correlation technique that assesses the level of coordination between the net external moment and the angle of the torso in the sagittal plane. In this paper, these methods are applied to a dataset of lifting motions of obese and normal weight participants to explore the utility of these modeling approaches on the assessment of potential risk in the lifting task due to obesity.