Background: This study aimed to clarify the changes in stiffness variables when maximal speed sprinting performance was developed through long-term training.
Methods: Nine well-trained male athletes performed maximal effort 60-m sprints before and after the completion of six months of winter training. In both experiments, sprinting motion at maximal speed was recorded with a high-speed camera and simultaneously ground reaction force (GRF) was measured. Spatiotemporal and stiffness variables were then calculated.
Results: Sprinting speed was significantly developed (P=0.001) through longer step length (P=0.049). While the leg stiffness did not change (from -539±126 to -558±180 N/kg/m) (P=0.686), the vertical stiffness significantly increased (P=0.001) from -1507±346 to -2357±704 N/kg/m due to increase and decrease in vertical GRF and descent of whole body center of gravity, respectively. Moreover, whereas knee joint stiffness remained constant (from -0.228±0.080 to -0.213±0.084 Nm/kg/°) (P=0.448), ankle joint stiffness was significantly developed (P=0.002) from -0.165±0.031 to -0.210±0.032 Nm/kg/° due to a respective increase and decrease in ankle plantarflexion moment and ankle dorsiflexion angle.
Conclusions: The results demonstrate that the development of maximal speed sprinting performance through longer step length is accompanied by increases in vertical and ankle joint stiffness, and this shows the importance of vertical and ankle stiffness for improving maximal speed sprinting performance. Findings of this study may assist with the planning of training programs for athletes.