[Aims] Vertical stiffness (Kvert), defined as the ratio of height change to ground reaction force during contact phase, has been used as the index of stretch shortening exercise (SSC). Hobara et al. estimated changes in Kvert during 400m sprint running, and reported it to peak in the phase between 50-100 m, it decreased after that. This phenomenon leads us to the hypotheses that decreased running speed in the latter part of long sprint event had related to the decrease in the ability of vertical jumping. Therefore the purpose of this study was to investigate the cause of decline in that latter part of long sprint running from a viewpoint of vertical stiffness. [Methods] Seventeen sprinters were divided into two groups, elites and controls, according to their personal best 400m time (49.23±1.84sec 46.36sec to 55.31sec). They run 300m using non-motorized treadmill (Curve, Woodway) in all their effort. Before and immediately after the sprint running, they had hopping jump for 15 times on the force platforms. Kvert and jump height (JH) during hopping was estimated by ground reaction data. [Results] As a results, 300m time were for 45.6±2.33sec and 49.8±3.56sec, in Elites and controls, respectively. After 300m sprint, JH decreased for 32% and 43% in elites and controls, respectively. Moreover, Kvert decreased for 21% and 29% in elites and controls, respectively. Main effects for JH and Kvert were seen in pre and post sprint conditions, although no main effects were seen among groups. [Conclusions] Deterioration of SSC performance may be a factor of decline in running speed in the latter part of long sprint, though no effect of performance level was seen
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