Biomechanical models are used to predict the physical stresses imposed on the musculoskeletal system. In general, two types of models, static models and dynamic models have been used to predict the stresses which occur while the body performs a lifting action. Static models predict the stresses which occur while the body performs a lifting action. Static models predict the stresses due to gravity while ignoring the inertial effects due to the accelerations of the load and body, while dynamic models consider both types of effects. Since lifting is a dynamic activity, there is concern that static models underestimate the stresses on the body. The studies described in the following section have postulated and verified that static models, by ignoring the inertial factors, substantially underestimate stresses. Most studies investigating lifting actions analyzed moments and forces on the spine, particularly at the L5/S1 disc, as the dependent variables of interest. According to NIOSH, the disc between the L5 and S1 vertebrae has the potential to incur the greatest moment in lifting and is one of the most vulnerable tissues to force-induces injuries (Waters, 1993). When examining the difference between static and dynamic predictions, the peak compressive force estimated by each model were typically compared. This peak stress usually occurs early in the lift, shortly after lift-off (De Looze et al., 1993), on average in the first 240msec (Garg et al., 1982) or about one-fifth of the way through the lift (Hall, 1985).