# Kinetic Comparison between Drop Jumps and Horizontal Drop Jumps in Elite Jumps and Sprinters
## 1 Introduction  
The kinetic evaluation of pyometric activity is essential for optimizing performance by identifying which exercises generate the most ground reaction force (GRF) [1, 2, 3], eccentric (EP) and concentric (CP) impulses [4, 5, 6], and rate of force development (RFD) [2], as well as the adequacy of fall height (FH) for maximal power output (Pw) [4]. Thus, kinetic assessment could be a helpful way to make practical decisions about including vertical or horizontal projection exercises at specific points in sports preparation.  
The kinetic evaluation of the drop jump (DJ) and the horizontal drop jump (HDJ) has been reported in the literature [7, 8]. Researchers have attempted to quantify exerciseintensity [2; 9; 10; 11; 12], establish differences between a limited number of pyometric activities [8; 12; 13; 14], and determine the best technique. For example, science considers that during rebound DJs, GRF can be 1.5 higher than that produced during countermovement DJs [15]. On the other hand, it was reported that the GRF is greater in the DJ than in the HDJ when the drop height is 40 cm [16]. The authors also report that, for unilateral DJs from the 20 cm box, there is no difference between vertical and horizontal impulses. Although we presume that the low value refers to the anteroposterior forces, in this research, it is unclear whether the mean GRF of the horizontal jump (714.6 \(\pm\) 167.2 N) is a measure of the anteroposterior forces of HDJs, or a measure of the vertical forces of HDJs; these aspects should be clarified in future scientific reports. A previous study [17] found that the time to the concentric peak of the GRF can account for 45-55% of the total jump time, meaning that the muscles still have significant time to continue to produce force after the concentric peak. In this regard, we have not found a report of the temporal phase of force production after reaching the maximum concentric peak. It has also not been reported how the muscle continues to apply force after reaching this maximum peak.  
In this context, it is known that several sporting movements are highly dependent on the application quality of Pw and RFD [18; 19; 20]. These are essential physical requirements [21] during pylemetric exercises, especially when FH induces short contact times. Therefore, it is unsurprising that many scientists include these assessments in pylemetric control to monitor their performance. Previous reports have assessed maximal eccentric and concentric Pw [19] and RFD [22] concerning vertical force tracing during jumps. They are based on two criteria: (I) that RFD is measured from the onset of contraction to any point on the force-time curve or between any two points on the curve [23; 24], and (II) that a subject can have as many RFD values as the number of time intervals within the force curve [21]. Thus, it could be interesting to know the RFD values, especially when the slope of the curve displays negative behavior after reaching the maximum peak of concentric force, i.e., the rate of force decrease (RFDe) of the DJ and HDJ in sprint and jumping athletes. To the best of our knowledge, this metric has not been previously reported, and there is a lack of knowledge about how muscles continue to develop force from peak concentric force to the take-off instant. As previously reported, no comprehensive study has yet been conducted to determine the relationship between kinetic variables and certain types of bilateral jumps [25]. Furthermore, we did not find any comprehensive studies of DJs and HDJs that show whether the eccentric impulse (PE) and concentric impulse (PC) are modified or tend to differ with increasing FH. Also, little has been reported on Pw in HDJs and whether it differs concerning DJs, though it could be considered that these variables constitute a key physical component in the performance of these sports disciplines. Therefore, the present study aimed to compare the kinetic variables of the DJ versus the HDJ in elite jumpers and sprinters.