The only tenable option for tissue load prediction is to utilize sophisticated modeling approaches. Once tissue loads in vivo have been esti mated, they can be applied to spinal specimens in vitro to evaluate tolerance levels and injury mechanisms. Data from both approaches will be presented in this article. Descriptions of the actual methods will be kept brief, although the interested reader is urged to consult Cholewicki and MThe low back region is an extremely complex mechani- cal structure, and direct measurement of tissue loading in vivo is not feasible. The only tenable option for tissue load prediction is to utilize sophisticated modeling approaches. Once tissue loads in vivo have been esti- mated, they can be applied to spinal specimens in vitro to evaluate tolerance levels and injury mechanisms.