## 4 Discussion
In a research study on a student population that exercises frequently, [PERSON] [11] found a statistically significant correlation between S5J and 10 m sprint time (r = \(-\)0.70). It could be concluded that performing a series of connected unilateral jumps is more demanding for the non-sprinter population and therefore their results are worse than shorter and less demanding tests used to assess lower extremity explosive strength. In their study, [PERSON] et al. [13] investigated the ground reaction forces in the concentric (505.9 \(\pm\) 91.9 N) and eccentric part (392.7 \(\pm\) 110.1 N) of the foot contact during the horizontal unilateral HCMJ in team athletes. According to [PERSON] et al. [35], the relative horizontal (R\({}^{2}\) = 61%) and propulsive (\(R^{2}\) = 57%) momentum of ground reaction forces during sprinting are better predictors of success in the 16 m sprint than vertical indicators of forces. Start and start acceleration have similar requirements, as the ability to generate a large horizontal force at the beginning of the distance determines success in sprint running [48]. [PERSON] [49] found that the average horizontal propulsive force of sprinters in the first stride after the block clearances is 526 N. This is the horizontal force of the sprinter. It is the horizontal velocity of movement of the body's center of gravity that is the key factor in generating a large vertical force of ground reaction, which is present in hurdling, unilateral jumps, and specific horizontal jumps used by athletes that generate the greatest horizontal velocity [50]. It could be speculated that untrained and/or insufficiently trained individuals might have problems tolerating these forces when performing jumps, based on the authors' experience. The values of the results of the regression analysis used to determine the functional relationship between the results of the predictor variable UHCJ20m and the criterion variable MRFS20m implied a moderate correlation, i.e., the influence of the unilateral cyclic jumps on the result in the test of the evaluation of the maximum running speed (Table 2). The data obtained showed that performance in the UHCJ20m test had greater predictive power for the MRFS20m test results than for the M100m and MRLS20m test results. Other research studies [6; 9; 47; 51] also found that horizontal jumps were more strongly correlated with maximum running speed than vertical jumps. The results of this research study confirmed the correlation between horizontal jumps and maximal running speed. The UHCJ20m [26] is a test of horizontal direction, unilateral and cyclic in nature, unlike a large number of horizontal jumps in many research studies, which include jumps such as STJ [5; 6; 24; 29] S5J [11] and UHCJ30m [27; 30]. The most commonly used and analyzed jumps in sprinting are the SLJ, the standing unilateral horizontal long jump, the drop horizontal jump, the drop unilateral horizontal jump, the STJ, and the S5J. Only the last two jumps are unilateral (although the take-off is bilateral) and cyclic (number of connected unilateral jumps). The greater the number of horizontal unilateral jumps (more connected jumps), presumably the better the predictability of the maximum running speed. [PERSON] [11] found a statistically significant correlation between the S10J test results and the 100 m sprint (r = \(-\)0.83), whereas the correlation between S10J and the 30 m sprint time was weaker (r = \(-\)0.67). The S5J results showed the same trend with slightly lower values for both distances. The UHCJ20m test results in this research study showed a lower correlation (r = 0.53) but can still serve as a predictor of success in sprinting, more specifically, the maximum running speed. It is likely that the correlation between the two tests would be higher/stronger if the research study had been conducted on elite athletes, due to their specific leg strength and the level of upper body strength [11].