## 3 Results  
Table 1 shows the results obtained with each type of shoe in each running time trial, and the effect of the type of shoe, the set, and their interaction. The type of shoe (i.e., CON vs. AFT) did not influence performance (F\({}_{(1.11)}\) = 0.2 and \(p\) = 0.70, \(\eta_{p}\)\({}^{2}\) = 0.016), but it significantly (\(p\) < 0.05) affected step frequency, vertical stiffness (post-), and the subjective perception of shoe flexibility (F\({}_{(1.11)}\) = 8.6, 4.1, and 13.7; \(p\) = 0.01, 0.05, and 0.00, respectively). The set (i.e., Time Trial 1 vs. Time Trial 2) significantly (\(p\) < 0.05) influenced performance, mean HR, post-test lactate levels, mean power, peak power, step amplitude, contact time, leg stiffness, forefoot comfort, and grip (F\({}_{(1.11)}\) = 13.4, 18.8, 5.3, 6.6, 4.1, 7.1, 3.6, 3.3, 4.0, and 3.4; \(p\) = 0.00, 0.00, 0.04, 0.03, 0.05, 0.02, 0.05, 0.05, and 0.05, respectively). The combined effect of shoe and set (i.e., Shoe x Set) was significant (\(p\) < 0.05) for step frequency, vertical stiffness (post-), vertical oscillation of the center of gravity, and subjective perception of flexibility (F\({}_{(1.11)}\) = 9.3, 4.1, 4.8, and 14.4; \(p\) = 0.01, 0.05, 0.05, and 0.00, respectively). The perception of flexibility decreased when the series order was CON-AFT (from 76.5 \(\pm\) 8.2 to 69.3 \(\pm\) 13.4%) and increased when it was AFT-CON (from 47.2 \(\pm\) 24.7 to 64.3 \(\pm\) 21.6%). Figure 3 shows the abovementioned interactions between the type of shoe and set (i.e., Shoe x Set) on the biomechanical variables. When comparing Time Trials 1 and 2, step frequency decreased when the order was CON-AFT and increased when the order was AFT-CON; the vertical oscillation of the centre of gravity was maintained and decreased, respectively; and the vertical stiffness after the test increased and decreased, respectively. Table 2 shows the results obtained with each type of shoe in each set depending on the type of terrain (i.e., Uphill, Downhill, Mixed), and the effect of footwear, the set, and their interaction. Footwear did not affect performance in any of the running segments analyzed (F\({}_{(1.11)}\) = 0.0, 0.7, and 0.6, \(p\) > 0.05), but it significantly (\(p\) < 0.05) affected the step frequency and vertical oscillation of the center of gravity during the uphill segment, and peak power during the downhill (F\({}_{(2.22)}\) = 5.6, 9.1, and 4.4; \(p\) = 0.04, 0.01, and 0.05, respectively). On the other hand, the time trials order affected performance during the uphill (F\({}_{(2.22)}\) = 45.1 and \(p\) = 0.00) but did not influence performance on the downhill or mixed terrain. Thus, during the uphill, mean and maximum HR, maximum pace, and mean and maximum power were significantly higher (\(p\) < 0.05) in Time Trial 1 compared to Time Trial 2 (F\({}_{(2.22)}\) = 36.1, 16.3, 9.5, 22.4, and 4.2; \(p\) = 0.00, 0.00, 0.01, 0.00, and 0.05, respectively). On the downhill, significant differences (\(p\) < 0.05) were observed in mean and maximum HR and maximumpace (F\({}_{(2.22)}\) = 9.6, 6.2, and 7.8; \(p\) = 0.01, 0.03, and 0.02, respectively), with no significant differences in the mixed terrain segment. In all segments, differences in biomechanical variables were observed between Time Trials 1 and 2, with step amplitude significantly decreasing on the uphill (F\({}_{(2.22)}\) = 19.7 and \(p\) = 0.00) and step frequency on the downhill (F\({}_{(2.22)}\) = 5.2 and \(p\) = 0.04). While running on the downhill and mixed terrain, the contact time significantly increased (F\({}_{(2.22)}\) = 8.3 and 5.3; \(p\) = 0.02 and 0.04, respectively), and leg stiffness decreased (F\({}_{(2.22)}\) = 9.7 and 6.0; \(p\) = 0.01 and 0.03, respectively).