The purpose of this study was to examine the influence of aspects of limb dynamics on variation in site of force application on tibial displacement during the Lachman test. Twenty-two certified athletic trainers and 12 model patients participated as subjects. Videotape analysis of clinician grip configurations (CGC) was made for certified athletic trainers during Lachman test performance. Presentation order of model patients was randomized across participant clinicians. Videotaped Lachman test trials were coded by classifying CGC according to thumb placement of the "tibia hand" (hand used to displace patient's tibia relative to femur) for each trial of the Lachman test. Categories represent the predominant CGC during at least 80% of the Lachman trials across model patients. This coding system has high inter-experimenter reliability in classifying grip categories (Newell et al., 1989). A model of the knee in the sagittal plane was developed to permit simulation of Lachman test performance. The model permitted examination of displacement of the tibia relative to the femur during the Lachman test. Anatomical model geometry was based on cadaver data (Nuno & Ahmed, 2001; Draganich et al, 1987). Motion of the lower leg was achieved by applying a force to the "posterior" surface of the shank; and, displacement of the shank relative to the femur was measured. CGC was classified into two categories: thumb on knee joint space (condition A); thumb on or distal to tibial tuberosity (condition B). Of the certified athletic trainers sampled, 84.2% demonstrated condition B although clinicians under condition A achieved a greater mean number of accurate assessments (p=.001). Model simulations of the Lachman test mimicked CGC conditions with force applied proximally (2 cm from knee axis), and distally (8 cm). Anterior translation of the tibia was greater under condition A (1.8 mm vs. 0.35 mm). Clinician grip configurations using distal "tibia hand" placement appear to alter tibial displacement relative to the femur. Ligamentous stability would therefore be masked during the Lachman test potentially hindering clinical evaluation accuracy. The model appears to capture the essential elements that influence the variability in which a group of subjects chose to execute the Lachman test.