# Effects of Plyometric and Short Sprint with Change-of-Direction Training in Male U17 Soccer Players
## 1 Introduction  
Soccer is a team invasion game, involving high-intensity efforts performed intermittently, and it requires divergent athletic traits (i.e., power, strength, endurance, agility, speed) for successful performance in competition [1]. During matches, decisive moments (i.e., gaining possession, conceding possession, and periods around goals) occur primarily during high-speed sprints [2]. In elite soccer, physical capacity, such as jumping, sprinting, and change-of-direction speed, are the determining factors in performance [3]. Time and motion analyses have shown sprints account for \(\sim\)3% of the total distance covered during matches between young soccer players [4]. Furthermore, the ability to change direction isan important physical attribute, given the wide range of in-game situations that allow for a sudden change-of-direction (CoD) [5]. Plyometrics is an important component of several team sports [6], and training is recognized as a safe and effective method to improve explosive actions and should be an important component of fitness programs for soccer players. Furthermore, pyometric exercises are often performed using jump training, and they improve muscle power [7; 8; 9]. Discussions around the optimal form of pyometric training continue. [PERSON] et al. [10] suggested that short-term pyometric training using a moderate volume of jumps produced similar enhancements in jumping performance, but greater training efficiency, compared with training using a high volume of jumps. [PERSON] et al. [11] found that if a moderate pyometric training volume was employed on a hard surface, the efficiency of adaptations in reactive strength would be doubled. Plyometrics consist of an eccentric contraction of the musculotendinous unit followed immediately by a concentric contraction (termed the stretch-shortening cycle (SSC)) [8]. The SSC improves the ability of the musculotendinous unit to produce maximum force in the shortest possible time [8]. Plyometric training is considered safe and efficacious for improving explosive movements, and should be a primary component of fitness programs in invasion games [12; 13]. Furthermore, [PERSON] et al. [14] noted that change-of-direction ability represents an important physical trait that should be included in training programs for youth soccer players. Recent review papers and meta-analyses have reported that \(\sim\)8 weeks of bi-weekly pyometric training improved high-intensity physical abilities (e.g., jumping, sprinting, agility) [15; 16; 17; 18]. Previous studies have recommended the incorporation of combined PSSCoD training into the soccer season to improve jumping, sprinting, and change-of-direction ability. [PERSON] et al. [19] reported that such training enhanced change-of-direction ability (Illinois agility test (ICODT) without a ball and 4 m \(\times\) 9 m shuttle run test (agility 4 m \(\times\) 9 m)) in prepubertal male soccer players. Additionally, [PERSON] et al. [20] noted that such training improved vertical and horizontal jump performance (squat jump and long jump), change-of-direction ability, and sprint performance over 10 m in prepubertal male soccer players. Furthermore, [PERSON] et al. [6] studied the effects of combined pyometric and short sprint with change-of-direction (PSSCoD) training in male U15 handball players. These authors reported significant yet small improvements in vertical and horizontal jump performance (39%, 29%, and 13% for squat jump, counternurement jump, and five-jump tests, respectively). These researchers reported significant yet trivial to small improvements in 5, 10, 20, and 30 m sprint times (9%, 7%, 7%, and 9%, respectively), but no gains in all repeated sprint ability (RSA) parameters. To the best of our knowledge, the present investigation is the first to have studied the effects of combined PSSCoD training in elite young soccer players (U17). Thus, the aim of this study was to evaluate the effects of replacing normal training in-season with combined PSSCoD training in elite male soccer players (U17).