## 4 Discussion
In that study [21], an enhancement by approximately 38% and 25% was reported for static and dynamic balance in the dominant leg of adolescent (12-13 years old) male soccer players. Similarly, the static, semi-dynamic as well as dynamic balance in younger (9-11 years old) male soccer athletes was enhanced following their participation in a 12-week balance training, comprising static one- and two-legged balance tasks, semi-dynamic balance tasks, along with walking and running on both stable and unstable surfaces [16]. Further, in elite junior (aged 16.0 \(\pm\) 0.5 years) male soccer players who were involved for 10 weeks at a frequency of twice a week in pyometric unloaded versus ankle-loaded (2.5% of body weight) training, there was an improvement in the work balance time score performed with open eyes in both groups [42]. Previous 6- to 8-week training interventions that have used a pyometric training protocol combining horizontally and vertically directed jumps found a decrease in the anteroposterior and mediolateral sway range by approximately 15% and 19% during two-legged static balance tasks with open and closed eyes in 9-13-year-old male soccer players [11], while an improved dynamic balance ability was seen in male soccer athletes of similar age to our athletes as well as in older ones [9; 10]. The disparity between the present findings and those previously reported might be attributed to the heterogeneity of training regimens. Training volume was higher in most of those studies [9; 16; 21; 37; 38], as compared to the current study. Solely, [PERSON] et al. [11] implemented the same training volume (i.e., 12 sessions for a frequency of training twice/week). However, their intervention consisted of a combination of horizontal and vertical jumps, which amounted to a greater total number of pyometric jumps. The difference in the pyometric training stimulus might explain the absence of changes in static balance ability that was observed here, since a meta-analysis concluded that pyometric training interventions have a significant but small effect size on static and dynamic balance performance [43]. Moreover, it has been shown that the transfer of postural balance adaptations is strongly associated with the context in which the physical activity or sport is practiced [13]. It is highly likely that differences in the content of balance exercises used in previous studies [16; 21; 42] could account for the observed disparity in results. Similar to [PERSON] et al. [27] and [PERSON] et al. [41], who subjected their athletes to a combined balance and pyometric training intervention, our soccer athletes practiced single-legged static stance tasks and dynamic displacements both on various bases of support and types of support surfaces (see Table 1). Even though the present results suggest a trend towards a slight improvement in single-legged balance performance, since CoP parameters were decreased by 0.2 to 1.9%, this study's training stimulus was probably not adequate to bring about significant changes, as previously reported [16; 21; 41; 42]. Static balance assessment based on CoP measures is considered as a reliable method to examine postural steadiness [31; 33; 34; 35; 36; 37]. With the exception of [PERSON] et al. 's study [16], previous authors, who have found improvements in static balance ability [21; 42], assessed performance based on the time score. It can be acknowledged that the time to complete a single- or two-legged balance task is very different to the CoP oscillations, which are being recorded within that same time period and reflect the center-of-mass effort to generate a corrective torque in order to counter the destabilizing gravitational torque [24]. [PERSON] et al. [41] also assessed CoP sway by means of recording the vertical ground reaction force, but their positive results refer to dynamic balance performance, thus limiting any direct comparison with the current findings. Plyometric training is a widely recognized method to improve and maximize muscle strength and power.