## 1 Introduction  
In high-level sports, measuring strength qualities independently is a fundamental tool to isolate which components need to be strengthened during training. Within the context of training, there is anecdotal testimony suggesting that 100 m and 400 m runners may require the use of different strategies for reactive strength training. However, we believe this assertion needs rigorous testing, as the current demands of a 400 m dash sprinter are not very different from those of a 100 m dash sprinter. By analyzing spilt times, i.e., every 100 m during the 400 m at the last World Championships (Appendix A), we observe that a 400 m athlete is essentially a sprint athlete and has a well-developed velocity characteristic. For both groups of athletes, pylometrics should not only be a practical training method [1], but also allow to isolate the measurement of lower limb power performance [2]. Previous studies have emphasized the importance of assessing jump height (JH) [3, 4] and ground contact time (GCT) [3, 4] in different exercises. The combination of these two variables computes the reactive strength index (RSI) [5]. The RSI has been and is established as a valid and reliable measure of explosive qualities and capturing real-time acquisition of behavior between eccentric and concentric actions [6, 7]. This variable is commonly applied in pyjometric training programs and was first described [5] as reactive strength and later used as an index by several researchers [7; 8; 9; 10]. In the original equation, the RSI is calculated by the ratio between JH and the GCT. However, in several studies, the RSI is also being calculated from flight time (FT) divided by GCT [10; 11]. However, caution is warranted, as this method tends to overestimate RSI values compared to its original equation [7]. Consequently, these two approaches for calculating the RSI are not equivalent and should not be used interchangeably [12]. The evaluation of the reactive strength variables of athletes is a useful tool in most sports [2]. Hence, several anaerobic disciplines use it [13], considering these could be a key factor for sports performance [14]. There may also be other variables to consider, such as the reactive capacity (RC), even though researchers confuse it with the RSI [15], although they do not represent the same variable. The RC was first defined by [PERSON] [16], and like the RSI, it is provided as a particular feature of the function and work of the neuromuscular system. It can be defined as the ability to develop a maximum impulse immediately after an eccentric action during a drop jump [16]. Despite this information, how RC correlates with other reactive strength variables is still unknown. Regarding the RSI, previous findings [3] with recreationally active individuals recommend performing pyjometric training from heights not up to 0.40 m due to the biomechanical differences found in jumps with bounces from 0.20 to 0.60 m. However, this was not the case with top athletes. Another study [10] with national-level athletes, who performed training programs for drop jump (DJ) from fixed heights of 0.30 cm, found an increase in vertical jump performance but did not take into account previous criteria on neuromuscular pre-activation [9]. Similar studies [17] found differences in the RSI with power athletes (jumpers, sprinters, and throwers; RSI = 2.19 \(\pm\) 0.58 cm) outperforming endurance athletes (RSI = 0.84 \(\pm\) 0.39). These findings confirmed the hypotheses of the researchers. When we take a closer look at the sprinters, there are commonalities, e.g., both for 100 m and 400 m disciplines that fall into the same realm of velocity. This could be crucial in justifying comparisons between these groups. However, to date, we have found no reports comparing reactive strength variables between the two groups. To our knowledge, no published literature to date has reported the percentage of RSI loss concerning the HF for these athletes.