Performance is known to decrease over repeated sprints, yet the relative shares of physical and technical components are not known. The recent validation of an instrumented sprint treadmill allowed us to measure vertical (Fv), horizontal (Fh) and total (Ftot) ground reaction forces applied at each step during sprinting on the treadmill. The ratio Fh/Ftot was used to describe the effectiveness of force application (similarly to what has been proposed in cycling mechanics) and compute an index of propulsive technique (IPT). PURPOSE: To quantify the effect of repeated sprints on force and power output capabilities, and on the effectiveness of force application onto the ground. METHODS: 12 trained subjects including 3 sprinters performed blocks of five 6-s sprints with 24-s passive rest periods between them and 2 min between blocks, until failure or four blocks (20 sprints) completed, on an instrumented motorized treadmill. Ftot, Fv, Fh and belt speed (S) were sampled at 1000 Hz, averaged for each push-off and used to compute PP as the product of Fh by S. Another performance parameter was computed as the distance covered over 4 s (D4s). The IPT was computed as the slope of the linear relationship between the ratio Fh/Ftot and S from the first step to that at top speed. Changes in variables were tested by t-tests between the average values of the two first and two last sprints of each individual series. RESULTS: Subjects performed series of 17.2 ± 3.6 sprints. For the first two sprints, PP and D4s were 17.8 ± 2.0 W/kg and 30.3 ± 2.5 m, respectively. PP, Ftot, D4s and the IPT all decreased significantly by 26.4 ± 8.9, 6.20 ± 5.79, 13.5 ± 8.01 and 21.1 ± 19.5 % (for all, p < 0.001), respectively. The change in Ftot was significantly (p = 0.001) lower than that in IPT, and Ftot and IPT were not correlated during the first two sprints, nor were their changes with fatigue. CONCLUSION: The physical capabilities were significantly reduced with repeated sprints fatigue and the associated decrease in performance. The more novel result is that the technical ability to apply force effectively also decreased, independently from these force capabilities. Thus, it seems that fatigue affects more the technical ability of force application than the physical capacity of force production, making these two components of repeated sprints performance worth considering.