###### Abstract  
This project investigated effects of 8 weeks of biweekly loaded combined glyometric and short sprint with change-of-direction training an in-season regimen of young soccer players. An experimental (n = 17, age: 16.5 \(\pm\) 0.5 years, body mass: 64.5 \(\pm\) 5.2 kg, height: 1.73 \(\pm\) 0.07 m,) and control group (n = 17, age: 16.7 \(\pm\) 0.5 years, body mass: 65.6 \(\pm\) 4.8 kg, height: 1.74 \(\pm\) 0.07 m) were tested pre- and post-intervention for squat-jump (SJ), countermovement-jump (CMJ), and five-jump test (5 JT), 10 m and 30 m sprint performance, change-of-direction ability, and dynamic balance performance. The experimental group (EG) outperformed the control group (CG) over 8 weeks in jumping (\(p\) < 0.001; d = 0.98-1.17), 10 m sprinting (\(p\) < 0.001; d = 0.94), change-of-direction ability (\(p\) < 0.001; d = 1.24), and dynamic balance performance (\(p\) < 0.001; d = 0.53-0.74). We conclude that adding biweekly loaded glyometric with short sprints and change-of-direction training to habitual training improves athleticism of young soccer players. Therefore, loaded glyometric with short sprints and change-of-direction training should be implemented as a part of research-informed soccer training. change-of-direction training; glyometric training; team sports; stretch-shortening cycle 40.0.0  
with brief periods of recovery [6; 7; 8]. In youth soccer, endurance, speed, and muscle strength are essential physical skills, meaning young soccer players are often selected when they demonstrate superiority over peers in one or several of these physical qualities [9]. Consequently, exercise programs should include stimuli to generate positive adaptations regarding the agility (ability to accelerate, change of direction) [10; 11; 12; 13]. [PERSON] et al. [14] noted that change-of-direction ability represents a key performance indicator that should be incorporated into soccer conditioning programs. Few previous investigations have explored whether the addition of loaded pyometric with short sprints and change-of-direction training into the soccer season is efficacious for improving jumping, sprinting, and agility. [PERSON] et al. [10] found a combination of 10-week loaded and unloaded combined pyometrics and short sprint training enhanced change-of-direction ability in elite junior male soccer players (U17). These researchers also noted significant improvement in sprint performance (5, 10, 20, 30, and 40 m), vertical and horizontal jumping, and change of direction ability. Furthermore, [PERSON] et al. [11] and [PERSON] et al. [12] observed improved change of direction ability, dynamic balance, vertical and horizontal jumps, and sprinting after pyjometric and short sprints with changes of direction training in prepubertal male soccer players. Mechanisms underpinning these adaptations are relatively well understood, but implementation of these training modes in youth soccer have not been examined thoroughly. Plyometric training exploits the use stretch-shortening cycle (SSC), characterized by an eccentric muscle contraction followed instantaneously by a concentric contraction [15]. The SSC can be summarized as improving the capacity of the neural system and muscle-tendon unit to produce maximum force in a short time [16]. In this context, improved ability to exert force in a short time (i.e., power) positively associates with field test performance in sprinting, agility, and jumping, which are all enhanced after glyometric training [17; 18; 16]. Recently, a systematic review of the literature reported pyjometric training improved muscle power in 13 of 16 studies analyzed, with improvements ranging from 2% to 31% [19]. Due to the overwhelming support of glyometric training to enhance muscle power, [PERSON] et al. [20] recommended including glyometrics in soccer players' habitual training program.