# The Effects of Loaded Plyometries and Short Sprints in U19 Male Soccer Players in Tunisia
## 1 Introduction  
Soccer is a sport with many important characteristics comprising technical, tactical, and physical aspects [1], combining cyclic and acyclic movements [2, 3]. In youth soccer teams, endurance, speed, and muscular strength are valued physical skills [4], so youth athletes have a greater change of selection when they demonstrate excellence in these abilities [5]. Therefore, applicable fitness traits are generally assessed and monitored, and typically include maximum speed, strength, change-of-direction (CoD) ability, balance,and flexibility [6]. Therefore, fitness training in young soccer players is imperative to achieve success in their soccer careers [7].  
Conceiving appropriate training programs for soccer players requires a detailed understanding of the physiological load placed on players of particular age groups and positions [8]. In high level soccer matches, particularly at the elite level, there is a well described requirement to produce high speed intermittently, and repeatedly [9; 10]--this ability to recover between each sprint, and maintain performance in subsequence sprints is known as repeated sprint ability (RSA). RSA is therefore considered a specific fitness requirement of soccer [8]. Time and motion analyses indicate youth soccer players cover an average of 8448 m during a match, 501 m at 16-19 km\(\cdot\)h\({}^{-1}\) and 428 m at \(>\)19.1 km\(\cdot\)h\({}^{-1}\)[11].  
Plyometric and sprint exercises have been used as training methods for increasing abilities such as jumping, sprinting, and change of direction performance [12; 13; 14; 15]. Several researchers have discussed the use of pyometric [16; 17; 18; 19] and sprint [20; 21; 22] training with additional external loading. Recently, it has come to light that a combination of training methods may be more efficacious than standalone approaches [23]. Indeed, some recent studies have reported improved fitness parameters after loaded combined pyometric and short sprints (LPaSS) training in soccer players [24]. Recently, [PERSON] et al. [24] studied effects of LPaSS training in male U17 soccer players and reported improved sprint performance, jumping, CoD ability, RSA, and balance performance.  
To our knowledge, there is a dearth of studies examining the effects of LPaSS training in under 19 (U19) soccer players. As such, the primary aim of the present investigation was to determine the effects of replacing some proportion of habitual soccer training with LPaSS on jumping, sprinting, agility, CoD ability, RSA, and balance in male U19 soccer players. We hypothesized that replacing some of regular training with 8 weeks of LPaSS training twice per week would improve both horizontal and vertical jump performance, sprint performance, and CoD ability when compared with the control group, who maintained habitual training. Specifically, we examined vertical and horizontal jump performance (i.e., squat jump (SJ), countermovement jump with arm swing (CMJA), and the five jump test (SJ)), sprint performance (i.e., 10 m and 30 m sprint), CoD ability (sprint with 90\({}^{\circ}\) turns (S90\({}^{\circ}\)) and sprint 9-3-6-3-9 m with backward and forward running (SBF)), RSA, and dynamic balance performance (Y-balance test).