## 4 Discussion  
The aim of the present study was to assess and compare jumping performance and MV in both bilateral and unilateral DVJs under conditions involving the incorporation or exclusion of ball catching. The primary findings indicate that, despite the absence of observable differences in traditional DVJ performance parameters (jump height, RSI and CT) when the ball was introduced, MV, as assessed by SampEn, proved sensitive to these variations. Specifically, a substantial increase in SampEn, with a large effect ES, was observed in the right leg when the ball constraint was included in the task (RB vs. RNB). In  
Figure 8: DVJ SampEn in different conditions. BB, bilateral DVJ with ball; BNB, bilateral DVJ without ball; RB, unilateral DVJ right leg with ball; RNB, unilateral DVJ right leg without ball; LB, unilateral DVJ left leg with ball; LNB, unilateral DVJ left leg without ball; ES, effect size. Level of significance at 5% indicated with \({}^{*}\). Figure 9: Limb asymmetry of the parameters analyzed under B vs. NB conditions. \({}^{**}\)\(p\) < 0.01 differences B vs. NB; B: Ball; NB: no ball; RSI, reactive strength index; CT, contact time. Negative values are indicative of raw scores being greater on the left limb. Critical thresholds for asymmetry were established at \(\pm\)10% [54]. addition, SampEn values were higher for the LNB condition as compared to RNB with a moderate ES (\(p<0.05\)), although trivial ES was noted in RB vs. LB. MV assesses regularity of movement, which is a recognized indicator of motor control [28]. Hence, MV assumes a crucial role in identifying the amount of perturbation present in a specific sport action [55]. Also, it provides valuable insights about the player's coordination characteristics, in addition to shedding light on the dynamics of the task [56]. While previous studies have analyzed the influence of performing a dual task during DVJs [25; 36; 52; 57] and in sport-specific variations of jumping tests [58; 59] on biomechanical and performance parameters, none of these investigations have evaluated MV under different task constraints. Furthermore, to the authors' knowledge, this is the first study to investigate the effect of adding a sport-specific constraint to a classic DVJ test. In the current investigation, a large and statistically significant increase in MV was noted upon the incorporation of a ball in DVJs executed with the right leg (RB vs. RNB, Figure 8). Likewise, a trend towards a similar effect with a moderate magnitude was observed in bilateral conditions; however, the results did not attain statistical significance (BB vs. BNB, Figure 8). These findings align with those reported in previous research [16; 17; 38] which demonstrated an increase in entropy when a sport-specific constraint, such as a game ball, was added during an isolated action. The ball catch task involves intercepting a moving object. For successful interception, it is necessary to perceive and anticipate the ball's trajectory by capturing information about its position, the direction and velocity of its displacement, and acceleration or deceleration [60]. The increase in MV observed in the present study could be attributed to a change in the system's coordination patterns or a combination of stability and adaptability of the movement induced by this specific constraint [17]. Regarding laterality, the right leg in the no-ball condition (RNB) was the side that showed lower MV and therefore could relate to greater task dominance. In the same condition, without a ball, the left leg (LNB) showed higher MV values, which can be explained by the natural lower-limb dominance of the subjects in non-specific sport-related tasks (all participants were right-limb-dominant). Interestingly, the addition of the ball constraint to the task produced a large, significant increase in MV in the right leg (RB vs. RNB), but trivial and not significant effects on the left leg (LB vs. LNB).