# Effects of Age and Sex on the Kinematics of the Sprinting Technique in the Maximum Velocity Phase
## 4 Discussion  
The comparison of adult men and women sprinters with systematically trained prepubescent track-and-field athletes during maximum velocity sprinting revealed that the spatiotemporal structure of the step parameters was significantly (\(p<0.05\)) different between AM and AF but not between PPB and PPG. This confirmed one of the hypotheses of this study. As for the other hypothesis, a significant (\(p<0.05\)) main effect of age was evident mainly for the ankle joint of both legs, as well as for the angular kinematics of the swing leg's knee joint. This did not support the hypothesis that the angular kinematics (angle and angular velocity of the lower limb joints) would not be altered between age groups as sprinting is considered a congenital ability. Based on the results, it is observed that both boys and girls exhibit lower sprint velocity at maximal sprinting compared to adult men and women. Regarding the sprinting technique per se, it is suggested that the anthropometric parameters (body dimensions, musculature, and fat tissue) influence sprint performance [64,65]. The leg length and the body height were found to be related to step length [66]. As children are smaller in size, there is a possibility that this influenced our findings. Regarding the other step characteristic, namely the step frequency, it was found that the boys' speed developed at a low rate from 8.8 to 12.1 years of age as a decreased stride frequency in the older boys within this age span was detected [40]. On the other hand, the speed of age-matched girls presented an accelerated improvement, which was accompanied with a stride length enhancement at the phase of maximal speed that was attributed to their probable ability to apply higher propulsive forces [56]. However, these sex-related differences in maximal sprinting were not confirmed in this study. This difference in sprint performance may be attributed to several other factors than the size differences that affect step length. Firstly, one possible explanation is the higher propulsive force that adults can apply compared to children during stretch-shortening cycle (SSC) movements, as previously confirmed in drop-jump tasks [67,68]. Male and female adults can generate more force relative to their body weight, resulting in greater sprinting velocities compared to boys and girls. Secondly, the time required to achieve maximal propulsive force may also be a contributing factor. Adults reach their maximum force output more quickly than children in SSC actions [67,68], and this probably enables them to generate maximal force at a faster rate during sprinting as well. The examined prepubescent athletes had a larger ratio of contact time within the duration of the step. This is related to the duration of the braking phase, which should be as short as possible [69]. To optimize the transition of the braking to the propulsive phase, foot placement plays a vital role [69]. Our findings regarding the BCM horizontal velocity of the ankle joint at touchdown suggest that the examined prepubescent athletes performed the foot placement with a blocking instead of a \"pawing\" action. This is a disadvantage for the fast transition from braking to propulsion, as well as for the application of optimum horizontal force. The application of horizontal force during sprinting is of utmost importance as power and horizontal force have been identified as the top predictors of maximal velocity within different ages and stages of maturity in females and males, respectively [55]. It is also suggested that less mature children differed significantly from the more mature in speed, step length, step frequency, vertical and horizontal force, and horizontal power. The lower sprinting performance of children is most likely caused by the lower mean propulsive forces and a shorter SL during maximal sprinting, with suggestions that the shorter SL is attributed to the lower vertical impulse and the lower height found in younger boys compared to older boys [40].