# Acceleration Capacity and Vertical Jump Performance Relationship in Prepubertal Children
## 4 Discussion  
The main aim of this study was to explore the relationships between several vertical and horizontal jump modalities and short-sprint performance in children. Our results revealed that vertical jump was correlated with all sprinting performances. The horizontal jump was only correlated with the 20 m performance. These results partly confirmed our hypothesis. The difference between the SJ and CMJ performance informs us about children's ability to use the elastic energy stored during the eccentric phase [37]. Thanks to this elastic energy, a better performance is observed during a CMJ than during an SJ for adults [38]. In this study, no difference was observed between the CMJ and SJ performance. This is consistent with previous studies highlighting an inefficient use of the stretch-shortening cycle in children [13]. The ability to efficiently use the stretch-shortening cycle generally increases during growth, in association with some changes in muscle and tendons [16] and neural properties [14,15]. Some studies showed that CMJ performance could be higher than SJ performance for children too [12,39], emphasizing the importance of taking into consideration the training level. A recent study including young gymnast girls showed a significant difference in DJ performance between the regional level and the recreational level, but not between the elite and regional levels [40]. The difference between the CMJa and CMJ performance can be considered a coordination indicator, reflecting the ability to use arm swings to improve jump performance. In this study, a significant difference was observed between CMJ and CMJa values, which is consistent with previous studies [39,41] and confirms the fact that children can enhance their jump performances using their arms. Relationships between jump performances and sprint performances were explored and some strong correlations were identified. Firstly, all vertical jump modalities (SJ, CMJ, and CMJa) were correlated with the sprint performances (5 m, 10 m, and 20 m). This agrees with previous studies that demonstrated a relationship between vertical jump and 30 m sprint performance in 7- to 10-year-old children [27] and a relationship between CMJ  
Figure 1: Correlation matrix between the different sprinting and jumping performances. 5 m, 10 m, and 20 m are the sprinting performances over the three different distances; SJ: squat jump; CMJ: countermovement jump; CMJa: countermovement jump with arms. Significant correlations are shown by * (_p_ < 0.05), ** (_p_ < 0.01), and *** (_p_ < 0.001). and 15 m sprint performance [28]. It was expected that the acceleration capacity would be correlated with SJ performance, and the results partially confirmed this hypothesis. As explained previously, SJ and CMJ performances are equal in children; for that reason, it is not possible to differentiate the relation of these two jump modalities with short-sprint performance. But for several reasons, it is reasonable to suppose that an SJ is more representative of one's acceleration capacity. Indeed, the SJ and short-sprint performance relationship could probably be explained by some similar parameters used to perform these two abilities. The SJ and sprint acceleration phase correspond to a predominantly concentric contraction of the lower limbs [42; 43]. Consequently, similar physiological factors could influence SJ and short-sprint performance. Indeed, during these two actions, rapid force production is crucial. The ability to rapidly produce force is influenced by muscle-tendon mechanical properties and neural contributions. Indeed, the tendons' efficiency to transfer muscular force is related to their stiffness. In this way, a positive correlation is identified between tendon stiffness and the rate of force development [44]. With children, a correlation between electromechanical delay (EMD) and tendon stiffness has already been shown [45]. Moreover, an increase in tendon stiffness after a resistance training protocol implies an EMD decrease in prepubertal boys [46].