# Stability of Running Stride Biomechanical Parameters during Half-Marathon Race
## 4 Discussion  
The primary aim of this study is to analyze the stability of the biomechanical parameters of the running stride among male trained athletes for endurance, specifically within the context of a half-marathon race. Previous research has predominantly utilized laboratory settings to predict performance outcomes based on biomechanical analyses, employing various protocols [13; 14]. In contrast, the investigation presented herein investigates the effects of fatigue on these parameters in the inherently dynamic and uncontrolled environment of an official half-marathon event. Findings are discussed with an emphasis on GCT, LSS, VO, and SL, delineating how fatigue alters these key performance indicators. In the examination of GCT, no significant differences were found (\(p\) = 0.38) and only small effect sizes were observed (\(\eta^{2}\) = 0.002) among the four race segments. These non-significant differences are due to the similar values of the GCT during the four race segments (208.6 \(\pm\) 17.4 ms, 208.5 \(\pm\) 16.1 ms, 210.0 \(\pm\) 14.6 ms, and 209.6 \(\pm\) 14.1 ms, respectively). Considering that previous research [7] whose purpose was to investigate whether a slow start to the race affects performance and kinematic changes concluded that kinematic changes do not seem to be affected by race pace, this would explain the non-significant differences in a half-marathon, which is a long-distance race. Referring to the values of the stability of this parameter, prior research [7] has documented that GCT values for trained athletes might escalate from approximately 260 ms at the onset of a race to 300 ms in states of heightened fatigue. However, the average GCT values for athletes participating in this half-marathon were consistently below this range, across all segments of the race, suggesting a distinctive dynamic attributable to the specific duration and demands of the half-marathon. This notion finds further support when considering that short-distance triathletes have demonstrated remarkably consistent GCT values at different performance thresholds: 207.88 \(\pm\) 1.37 ms at the first ventilatory threshold, 191.35 \(\pm\) 2.94 ms at the second ventilatory threshold, and 176.33 \(\pm\) 4.5 ms at maximum aerobic speed during incremental tests to exhaustion [22]. However, previous studies [2] that analyzed the influence of fatigue on biomechanics and physiological parameters based on running progression highlighted that the biomechanical parameters showed significant alterations, such as contact time and duty factor, even with a small change in perceived fatigue. In the same line, studies [6] that evaluated kinematic changes between km 8 and km 40 of a marathon in trained runners also identified increased contact time. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Sphericity**} & \multicolumn{3}{c}{**RM ANOVA**} \\  & \(\mathbf{W}\) & \(\mathbf{p}\) & \(\mathbf{\varepsilon}\) & \(\mathbf{SS}\) & \(\mathbf{df}\) & \(\mathbf{MS}\) & \(\mathbf{F}\) & \(\mathbf{p}\) & \(\mathbf{\eta}^{2}\) \\ \hline GCT & 0.13 & 0.04 & 0.46 & 13.12 & 1.37 1 & 9.55 1 & 0.96 & 0.38 1 & 0.002 \\ LSS & 0.02 & \textless{}0.001 & 0.47 & 0.19 & 1.41 1 & 0.13 1 & 5.52 & 0.03 1 & 0.004 \\ VO & 0.18 & 0.09 & 0.52 & 0.01 & 3 & 0.005 & 0.23 & 0.87 & 0.002 \\ SL & 0.08 & 0.01 & 0.45 & 0.0009 & 1.34 1 & 0.007 1 & 1.07 & 0.35 1 & 0.001 \\ \hline \hline \end{tabular} 1  
\end{table} 
Table 3: Repeated measures (RM) ANOVA results for GCT, LSS, VO, and SL measurements. Regarding LSS, this parameter emerged as the singular metric showcasing statistically significant variations, notably between the initial two segments of the race (\(p\) = 0.03), with a particular emphasis on the contrast observed between the first and second segments (\(p\) = 0.015). Despite the statistical significance, the practical implications of these differences appear limited, given the small effect size noted across the cohort of eight athletes (\(\eta^{2}\) = 0.004).