# Power Up: Comparing PAPE Responses in Free-Weight vs. Flywheel Resistance Training Systems
## 4 Discussion
The differences between these results may be due to the way exercise intensity was matched, which could have led to different acute responses. Since flywheel training systems do not have a maximum load (1 RM), unlike free weights, attempting to match training intensities between both systems can be highly inaccurate. A possible solution to this issue is the use of peak power with a given load [1,6,12]. However, similar peak power minimum values can be attained at various flywheel moments of inertia [21]. Trying to match intensities through the MPV seems to be a more accurate solution, as MPV considers the entire concentric phase and is the most used parameter for monitoring free-weight intensity in real time [17,19,21,23]. Nevertheless, similar intensities in both systems, measured through MPV, result in different kinetic and kinematic responses during exercise. Future studies should consider using MPV to match intensities between systems and at other post-exercise times, as it has been shown that the PAPE effect can remain effective until 10 min [10,11]. Despite similar outcomes observed in CMJs, the peak force reached during the vertical jump was only reduced in the group that trained with free weights (Figure 2). A possible explanation for these differences is that, due to muscle fatigue, the jumping technique might have been altered in the free-weight group. It has been shown that an increase in the center of mass displacement during the vertical jump can lead to lower peak forces [27]. However, CMJ performance and the peak force achieved during the jump are not necessarily related [27], which is why they show different behavior despite a similar decrease in vertical jump performance in both groups. Future studies should investigate the behavior of the center of mass during CMJs to assess the effects of fatigue or PAPE on vertical jump technique. Due to the differences in the force application vectors between linear sprint tests and vertically oriented exercises, the literature recommends selecting exercises with biomechanical similarity to the physical skill being targeted [28,29]. This biomechanical mismatch may explain the absence of sprint PAPE in the current study, as the force vectors involved in sprinting (10 m) are horizontal, while exercises like squats primarily target vertical force application. Therefore, the literature shows that the PAPE effects of squats are more effective on vertical jumps than on exercises focused on horizontal movements, such as sprints or changes in direction [28,29]. Despite this, positive PAPE effects (ES > 0.5) on 10 m sprint performance have been observed following a strength training protocol with flywheel systems [6]. Our results show that performance in T10 is not influenced by either of the two exercise protocols studied. Similarly to CMJs, the literature shows inconsistency regarding the differences in PAPE on linear sprint performance when comparing flywheel and free-weight bouts. In this regard, two studies show that performance in 5 and 30 m sprints were not influenced 3 min after performing a resistance training session with either free weights or flywheel devices [1, 16]. On the other hand, [PERSON] et al. [6] showed performance improvements (ES > 0.46) in both training groups on the 30 m sprint 4 min post-exercise. It seems difficult to reach a conclusion due to the lack of available comparisons in the literature. As previously explained, the differences may be attributed to the way training intensities have been matched (peak power vs. %1 RM). Future studies should aim to compare the differences in PAPE using exercises that closely mimic the force application vector during the initial phases of the sprint [2, 30]. This study is not without limitations. Although a very similar adjustment was made to match exercise intensities, the comparison between free weights and flywheel devices was only conducted individually with a single load or intensity.