Orizontal force. This ability represents how effectively the total force developed by the lower limbs is applied onto the ground, despite increasing speed during the acceleration phase. Methods: Twelve physically active male subjects (including two sprinters) performed 8-s sprints on a recently validated instrumented treadmill, and a 100-m sprint on an athletics track. Mean vertical (FV), net horizontal (FH), and total (FTot) ground reaction forces measured at each step during the acceleration allowed computation of the RF as FH/FTot and an index of force application technique (DRF) as the slope of the RF-speed linear relationship from the start until top speed. Correlations were tested between these mechanical variables and field sprint performance variables measured by radar: mean and top 100-m speeds and 4-s distance. Results: Significant (r > 0.731; P < 0.01) correlations were obtained between DRF and 100-m performance (mean and top speeds; 4-s distance). Further, FH was significantly correlated (P < 0.05) to field sprint performance, but FTot and FV were not. Conclusions: Force application technique is a determinant factor of field 100-m sprint performance, which is not the case for the amount of total force subjects are able to apply onto the ground. It seems that the orientation of the total force applied onto the supporting ground during sprint acceleration is more important to performance than its amount....

Recent studies have brought new insights into the evaluation of power-force-velocity profiles in both ballistic push-offs (eg, jumps) and sprint movements. These are major physical components of performance in many sports, and the methods the authors developed and validated are based on data that are now rather simple to obtain in field conditions (eg, body mass, jump height, sprint times, or velocity). The promising aspect of these approaches is that they allow for more individualized and accurate evaluation, monitoring, and training practices, the success of which is highly dependent on the correct collection, generation, and interpretation of athletes’ mechanical outputs. The authors therefore wanted to provide a practical vade mecum to sports practitioners interested in implementing these power-force-velocity–profiling approaches. After providing a summary of theoretical and practical definitions for the main variables, the authors first detail how vertical profiling can be used to manage ballistic push-off performance, with emphasis on the concept of optimal force–velocity profile and the associated force–velocity imbalance. Furthermore, they discuss these same concepts with regard to horizontal profiling in the management of sprinting performance. These sections are illustrated by typical examples from the authors’ practice. Finally, they provide a practical and operational synthesis and outline future challenges that will help further develop these approaches.

SUMMARY: The speed of the initial 30 m of an all-out run from a stationary start on a flat track was determined for 12 medium level male sprinters by means of a radar device. The peak speed of 9.46±0.19 m s–1 (mean± s.d.) was attained after about 5 s, the highest forward acceleration (af), attained immediately after the start,amounting to 6.42±0.61 m s–2. During acceleration, the runner's body (assumed to coincide with the segment joining the centre of mass and the point of contact foot terrain) must lean forward, as compared to constant speed running, by an angle α=arctang/af(g=acceleration of gravity). The complement (90–α) is the angle, with respect to the horizontal, by which the terrain should be tilted upwards to bring the runner's body to a position identical to that of constant speed running. Therefore, accelerated running is similar to running at constant speed up an `equivalent slope' ES=tan(90–α). Maximum ES was 0.643±0.059. Knowledge of ES allowed us to estimate the energy cost of sprint running (Csr, J kg–1m–1) from literature data on the energy cost measured during uphill running at constant speed. Peak Csr was 43.8±10.4 J kg–1 m–1; its average over the acceleration phase (30 m) was 10.7±0.59 J kg–1 m–1, as compared with 3.8 for running at constant speed on flat terrain. The corresponding metabolic powers (in W kg–1) amounted to 91.9±20.5 (peak) and 61.0±4.7(mean).