# Stability of Running Stride Biomechanical Parameters during Half-Marathon Race
## 1 Introduction  
Maintaining consistent movement patterns throughout a running event presents a significant challenge [1]. Deviations from these patterns can not only lead to decreased performance but also exponentially increase risk factors and contribute to injuries [2]. Fatigue stands out as one of the major factors behind this performance decrement and the ensuing issues [3]. From a physiological perspective, the metabolic cost of running at a submaximal constant speed is influenced by various factors, including fatigue and associated kinematic alterations [4]. The influence of fatigue on biomechanical parameters in endurance sports has been shown to modify stride frequency (cadence) and length (SL), ground contact time (GCT), vertical oscillation (VO), and leg spring stiffness (LSS), with variations being multiple and variable between athletes and conditions. However, the most relevant variations are primarily found in these parameters [5].  
Regarding SL, several authors [6; 7; 8] have observed a reduction in fatigued states compared to non-fatigued states. Numerous studies [2; 6; 7] show an increase in GCT in the presence of fatigue, potentially due to a reduction in muscle stiffness or LSS [6; 9; 10]. Concerning VO, a decrease has been noted [7], with some authors [11] suggesting that this reduction may result from diminishing strength capacity of the main muscles in the lower extremities. As a strategy to enhance running economy, [PERSON] [12] proposed that reducing GCT while maintaining stride frequency could lead to greater LSS, larger stride angles, and shorter swing times, thereby optimizing running technique.  
The analysis of biomechanical parameters in half-marathon and marathon races is particularly relevant--for example, studies on predictive variables of half-marathon performance for male runners [13], the comparison of half-marathon runners according to theirperformance level [14], and the concurrent evolution of biomechanical and physiological parameters with acute fatigue induced by running [2]. In fatigued states, trained runners have been shown to reduce their stride frequency compared to a non-fatigued state [4, 6, 8], likely due to the muscle's reduced force generation capacity [4]. Conversely, other studies [11, 15, 16] found increases in stride frequency, with [PERSON] et al. [7] and [PERSON] et al. [11] observing no significant differences.  
With the emergence of portable and low-cost equipment that allows data collection in field sessions, training, and competitions, alternatives are offered over older methods that require well-equipped research laboratories [17]. In this way, information more applicable to current sports practice is discovered as researchers can move participants to more sport-specific environments [18]. This alternative highlights the potential of these devices for gait analysis but without the corresponding limitations of traditional laboratory technology [19]. For assessing spatiotemporal parameters, the Stryd Running Power Meter has been widely studied in athletes to analyze the absolute reliability and concurrent validity of the Stryd system for the assessment of running stride kinematics at different velocities [20], as well as the agreement between spatiotemporal gait parameters from two different wearable devices and high-speed video analysis [21]. Additionally, the influence of biomechanical parameters on performance in elite triathletes has been analyzed [22].  
Therefore, the main purpose of the present research is to analyze the stability of biomechanical parameters of the running stride of male trained athletes during a half-marathon competition, focusing on changes in SL, LSS, VO, and GCT. This approach offers new perspectives for optimizing the training of biomechanical parameters in running.