Sprint running: how changes in step frequency affect running mechanics and leg spring behaviour at maximal speed.

The purpose of this study was to investigate the changes in selected biomechanical variables in 80-m maximal sprint runs while imposing changes in step frequency (SF) and to investigate if these adaptations differ based on gender and training level. A total of 40 athletes (10 elite men and 10 women, 10 intermediate men and 10 women) participated in this study; they were requested to perform 5 trials at maximal running speed (RS): at the self-selected frequency (SFs) and at SF +/- 15% and +/- 30% SFs. Contact time (CT) and flight time (FT) as well as step length (SL) decreased with increasing SF, while k(vert) increased with it. At SFs, k(leg) was the lowest (a 20% decrease at +/- 30% SFs), while RS was the largest (a 12% decrease at +/- 30% SFs). Only small changes (1.5%) in maximal vertical force (F-max) were observed as a function of SF, but maximum leg spring compression (Delta L) was largest at SFs and decreased by about 25% at +/- 30% SFs. Significant differences in F-max, Delta y, k(leg) and k(vert) were observed as a function of skill and gender (P < 0.001). Our results indicate that RS is optimised at SFs and that, while k(vert) follows the changes in SF, k(leg) is lowest at SFs.