the primary purpose of the study was to calibrate and validate a shoe impact machine designed to replicate heel strike impact force produced during running. the secondary purpose was to compare impact force attenuation magnitudes of four selected brands of running shoes. a major focus of footwear research has been on heel strike impact force due to its link to pain and injury (frederick, 1984; nigg, 1986; nigg, cole, bruggemann, 1995). however gross participant gait variation during testing has made it difficult to consistently measure and compare impact forces between shoes. to correct for this variance, an ideal testing method would be mechanical simulation of heel strike to validate actual human response (frederick, 1986, b). eleven healthy male participants performed 25 trials of barefoot force platform running at 3 m sec. using the vertical ground reaction force (vgrf) curves generated, mean barefoot impact force values were calculated. an impact machine was calibrated to the mean barefoot impact force scores produced from the force platform running for each participant. the impact machine then duplicated 5 heel strikes using four selected brand name running shoes. all impact force data was represented in percent body weight to normalize each shoe’s performance magnitude. impact machine validity was established through a paired sample t-test. no significant differences were found between barefoot running and the barefoot impact machine results where, t (11) = .222, p > .05. the results demonstrate that the impact machine generated equivalent impact force results compared to running over a force platform using multiple trials. a one-way analysis of variance (anova) revealed significant differences between midsole attenuation rates between the four pairs of running shoes; where, f(3,40) = 5.766, p < .05. scheffe’s post hoc comparison determined that nike was significantly different from adidas and new balance. no other significant differences were found. nike had the greatest attenuation rate absorbing 7.9% of the impact force per step followed by saucony 6.5%, then adidas 4.6%, and finally new balance 4.5%.