Sprinters are often coached to increase their sprint running velocity by minimizing the horizontal deceleration force during the first half of the foot contact phase. The present study was undertaken to clarify the relationship between changes in the horizontal velocity of the body's center of gravity (CG) during the foot contact phase and sprint running velocity. The subjects were 26 male sprinters (100 m personal best record : 10.27-11.50 s). The experiments were carried out on an allweather track into which a force platform was planted. Subjects performed sprint running at their maximal effort. The ground reaction forces were recorded and the subjects were videotaped from the side (100 fps). The horizontal distance from the toe to the CG at the moment of foot touch-down and foot release showed no significant correlation with the maximal sprint running velocity. The duration of deceleration decreased (r=-0.517, p<0.01) and that of acceleration showed a tendency to decrease (r=-0.385, p=0.0519) with the increase of the maximal sprint running velocity. The peak forces of deceleration and acceleration increased (r=0.542, p<0.01 ; r=0.442, p<0.05) with the maximal sprint running velocity. The rate of deceleration and acceleration of the CG during the foot contact phase calculated from the impulse of the horizontal ground reaction force showed almost a constant value despite the big difference in the maximal sprint running velocity. The present results suggest that reducing the rate of CG deceleration during the foot contact phase would not improve the maximal sprint running velocity. The ability to develop a higher acceleration force to the ground moving faster to the backward relative to the body's center of mass during the shorter foot contact phase is probably a major factor in determining the maximal sprint running velocity.