## 1 Introduction  
Triathlon is an endurance sport that comprises a sequential swim, swim-to-cycle transition, cycle, cycle-to-run transition, and run over a variety of long or short distances [1]. Standard races are stipulated by the International Triathlon Union (ITU), including sprint distance (750 m swimming, 20 km cycling and 5 km running) and Olympic distance (1.5 km swimming, 40 km cycling and 10 km running). Although the influence of the segments on the overcome result has been widely studied [2, 3, 4, 5, 6], the running segment has been the most studied. In the running segment was found the greatest variation in times for all male world championship triathletes [7]. Previous findings also have shown that running performance is the primary determinant of success in high-level short-distance triathlon races [8]. Other authors concluded that strategies to improve time in the running segment should be the main focus in the preparation of the short-distance triathlon [4]. However, to date, the physiological [9] and biomechanical changes in the performance of the world's best elite triathletes in short-distance triathlons have not been widely investigated. Concerning the triathlon performance factors, some authors differentiate between an ergogenic analysis for the determination of the internal load and an analytical analysis for the determination of the technical and tactical physical conditioning factors [10]. Internal load values have been previously studied in elite triathletes [10]--for example, for prescribing the heart rate (HR) zones for training from cycling to running [11]--to determine their significant maximum oxygen uptake (VO\({}_{2}\)max) [12, 13, 14]. Nevertheless,performance in triathlon has been associated with the capability of the triathlete to exercise at a lower percentage of VO2 max, which is influenced by different factors such as aerobic power, economy of movement and ventilatory threshold 2 (VT2) [15]. The influence of biomechanical factors on performance has also been widely studied. [PERSON] [16] classified them as spatiotemporal, kinematics, kinetics and neuromuscular, although running speed is mainly defined by spatiotemporal parameters, such as step frequency (SF) and step length (SL), which are mutually dependent. Although from a physiological and training point of view running performance has been widely studied, the possible influence of spatiotemporal variables on performance is still an issue of discussion [17]. Even more in elite triathletes due to the lack of analytical analysis of the running segment [10], unlike trained and novice runners [17; 18; 19]. To understand the influence of biomechanical parameters on performance, anthropometric characteristics must be considered because some of them influence the running success in triathlon [20]. In the last few years, there is a tendency to produce low-cost, portable gait analysis equipment, which has a great advantage over previous methods of analysis that have generally required well-equipped research laboratories [21]. [PERSON] et al. [22] point out that, from a practical point of view, through accelerometry it is possible to measure the participants in a more natural environment instead of an artificial laboratory. This is important for interpreting the data, taking into account the specificity of the sport because some biomechanical variables, such as leg stiffness, have been shown to influence performance [23; 24] while running in specific situations rather than in non-specific situations, such as vertical jumps [18; 19]. Currently, Stryd (Stryd Summit Model, Boulder, CO, USA) is a practical portable device that is reliable for measuring running metrics, classified as adequate for running assessment [25]. The concurrent validity of Stryd as compared to OptoGait was low-moderate for contact time (CT) and flying time (FT) and excellent for step length (SL) and step frequency (SF) [25].