# Kinetic Comparison between Drop Jumps and Horizontal Drop Jumps in Elite Jumps and Sprinters
## 4 Discussion
The previous study also reports an increase in Pc, which could be evidence of more pronounced knee flexion to increase force production and achieve greater jump height. At this point, the athlete may begin to change the jumping technique [15] due to excessively increased eccentric loading, thus affecting reactive strength. It was also observed that when the vertical force graph is fully pointed, the maximum concentric force is reached at the beginning of the concentric phase; therefore, the eccentric phase duration is equal to the time in which the maximum concentric force is achieved. This behavior has not been previously reported in the research we reviewed. This is the first study to compare the results of the GRFC on the vertical and horizontal axes of the DJ and HDJ. It was found that group A (the vertical axis of the DJ vs. the vertical axis of the HDJ) had significant differences in all sets of heights (Table 2), demonstrating that the vertical GRFC is always higher in DJs than in HDJs. This may be explained by the fact that during HDJs, after the velocity reaches 0 m/s, the body simultaneously initiates both a vertical upward and a horizontal forward displacement, splitting force production into both components. However, a previous study [17] showed that the ground contact time is longer in HDJs than in DJs, which hinders the possibilities of reactive work with this exercise and the multiplicity of strategies for pylemetric training. Behind these results, coaches may have a multiplicity of strategies for pylemometric training. For a long time, pylemetric understanding in athletics was limited only to vertical projection, but it is known that most of its activities include a horizontal component. Research has shown that horizontal pylemetric exercises in the program design adhere to the principle of specificity. Numerous studies show improvements in pylemetric training performance when exercises are biomechanically specific to the plane in which they are performed [13]. In this sense, as explained before [17], HDJs could be better used to train movements in which the ground contact times are longer and higher concentric components, such as the acceleration phases of a sprint, as well as to improve push-off capacity [39] during unilateral and bilateral horizontal jumps. This study also underlines that the anteroposterior force peak in HDJ always occurs later than the maximum vertical force. In addition, the impulse showed significant differences with moderate to large ES. Furthermore, during the DJ, the PE is always lower than the PC, but for the HDJ this behavior tends to reverse with increasing height (Table 2). Another finding is that the vertical impulse of the concentric phase for both exercises does not seem to be affected by increasing height, which was also corroborated in previous studies [4; 5]. Furthermore, as impulse increases, ground contact time also tends to increase. In this sense, the trainers should be careful because an increased impulse could affect reactive strength variables, depending on the technique used (e.g., Pc = 350 j with high force and short time vs. low force with a long time). The power outputs were already expected, as power is a product of force times velocity, and their relationship has been widely documented [40]. The concentric power outputs found in this study were based on instantaneous peak power. Other studies [19] are unclear on whether power reports are made by calculating the maximum GRF multipliedby the maximum speed, where the results may be overestimated. Power outputs between different FHs showed significant differences. For DJs, the greater power was produced in DJ40, although the difference in means compared to DJ50, which is not as high, could be considered by coaches for optimal load determination. This slight difference in FH metrics has been explained above [17]. For HDJs, it can be observed (Table 1) that HDJ40 presents greater PW values and could be considered the optimal load for power production. In contrast, the HDJ50 PW drops drastically.