# The Effects of Flywheel Training with a Portable Device on Physical Performance in Soccer Players
## 4 Discussion  
This study analyzed the effects of training with portable, low-cost RIDs on the performance of senior soccer players when performing sprints, CS, and COD. The main finding of this study is that training resisted by portable and low-cost RIDs improved the COD and CS ability of senior soccer players. Change of direction (COD) is a crucial skill that determines a soccer player's performance during a match. In many situations, gaining an advantage requires the ability to change direction faster than the opponent [1,7]. In fact, more than 700 CODs have been recorded in a single professional soccer match [27]. In our study, we obtained a V-Cut improvement of 4.12% over 8 weeks of training. These improvements are similar to those obtained in handball players who resisted the movement with traditional RIDs, using a training period duration and weekly frequency similar to ours and a daily training volume above that used in this study [22]. Other studies have reported findings that are similar to those observed in this investigation regarding the COD variable following the implementation of a training program with RIDs. For instance, [PERSON] et al. [28] observed significant improvements in 90-degree COD performance in young team-sport athletes following RID training performed both bilaterally and unilaterally. Notably, only unilateral training led to enhancements in both the dominant and non-dominant legs. These findings reinforce the exercise selection in this current study, where both exercises in the training program were performed unilaterally. Specifically in soccer players, [PERSON] et al. [21] reported results similar to those of this study, demonstrating significant improvements in COD performance in the group that trained with RIDs after six weeks of training. Additionally, [PERSON] et al. [27] determined that approximately 80% of CODs performed in Premier League matches occurred at angles between 0 and 90 degrees. Consequently, the V-CUT test appears to be a suitable method for assessing COD performance in soccer players, as it reflects the demands of the sport. Both this current study and the research conducted by [PERSON] et al. [29] reported significant improvements in the V-CUT test, which translate into enhanced performance in CODs involving angles of 90 degrees or less. This is the first study to apply a low-cost, portable RID training protocol and analyze its effects on CS performance. The CS is a resource used by players to avoid offside situations and to evade, follow, or draw the opponent [12]. As a result, it plays a crucial role during a match, both in offensive and defensive situations. In this study, a significant performance improvement was obtained in the CS performed to the right (\(-2.58\%\)), and there were indications of significance in the CS performed to the left (\(-1.27\%\)). According to [PERSON] et al. [12], we observed that in our sample there was a weak side in CS, with this side being the one on which greater time was spent to complete. A possible explanation for these results is that the percentage of right-footed players in both the EG (72.7%) and the CG (83.3%) was higher than that of left-footed players. It is known that soccer players have a better COD ability with the dominant leg [30]. This could explain why, in our sample, the performance in the CS in the pre-test was better towards the left side (CS10l and CS20l). In the post-test, these differences between the two sides were balanced, but only in the EG was it due to an improvement in CS performance towards the weak side (CS10r and CS20r). Further studies are needed to confirm if the improved balance between the strong and weak side of the CS relates to player performance enhancement. Based on this study, a low-to-moderate, non-variable training volume and a fixed external load may be sufficient to achieve positive adaptations in COD and CS in senior soccer players.