## 4 Discussion  
The present systematic review and meta-analysis aimed to synthesise and compare the effects of different types of stretching included in the warm-up on jumping performance and ROM. The main finding of this meta-analysis determines that SS in the warm-up decreased the height in the vertical jump; however, DS improved the height. Furthermore, both static and dynamic stretching in the warm-up improved the range of motion of lower-limb joints. Regarding CMJ (height), the meta-analysis shows significant differences between static and dynamic stretching in the warm-up, with DS showing an improved tendency and SS a negative tendency. The percentage of change in the jump was 1.8% with respect to DS and \(-\)1.6% to SS. The findings of the meta-analysis in DS confirm the results shown in previous studies. Positive effects of DS are shown on force and power, increasing the height of the vertical jump with a percentage of change of 5.04% and 2.32% [54; 55]. Several studies have concluded that vertical jump performance can be very relevant for evaluating performance in some sports [21]. It is considered a motor skill closely related to maximal strength, sprinting ability, and change of direction [23; 24; 56]. These improvements can be attributed to the voluntary, active, and rhythmic contractions of the muscles associated with dynamic stretching that can aid the warm-up process [57]. DS could contribute to warm-up effects by increasing muscle temperature, leading to a decrease in the viscous resistance of the muscles and, thus, an increase in tissue extensibility [7]. Several studies suggest that the increase in body temperature achieved by the warm-up is strongly related to jumping performance [58; 59]. The results obtained in the meta-analysis related to the negative tendency of the SS in the warm-up in the height of jump (percentage of change \(-\)0.04%) are in agreement with those obtained by [PERSON] (2019), who reported a significantly decreased vertical jump height after SS in the warm-up (percentage of change \(-\)2.6%) [15]. The negative effects of SS could be due to an inhibited production of force in the contractile component of the muscle [60], changes in viscoelastic properties of the tendon, and increasing elasticity [61]. After SS, both muscle and tendon production and force transfer are less effective [15]. However, the findings of the current study do not support the previous research of [PERSON] (2012) and [PERSON] (2020), who observed that SS did not lead to a decrement in vertical jump performance [20; 62]. This rather contradictory result may be due to the exposure time of SS. Prior studies show that the amount of SS could affect strength loss less or more, revealing that larger volumes of SS have a greater negative effect on subsequent performance compared with smaller volumes of SS, thus explaining the different results in the literature [63]. The literature determines that exposures of up to 1 min do not negatively affect performance in sports requiring high levels of strength; however, breaks of at least 4 min after stretching are recommended [64]. Therefore, previous studies suggest that the duration of SS can increase the distensibility and reduce the stiffness of the muscle-tendon unit. Nevertheless, our meta-regression results did not show any association variables. In our study, a meta-regression was carried out to establish the relationship between training protocols (series, repetitions, and rest) and their influence on the variable jump height. No relationship was found to corroborate that the duration of SS in the warm-up can be an influential factor in subsequent vertical jump performance. These findings suggest that further studies are needed to analyse the impact of training variables on jumping performance [65]. The results of our meta-analysis about the effect of static and dynamic stretching on ROM show no significant differences between types of stretching. A percentage change of 10.0% and 12.5% was obtained for static and dynamic stretching, respectively.