**1. Introduction**

The high hurdle race is one of the most technically demanding athletic events, and from a biomechanical standpoint, the hurdle race is a combination of a cyclic sprint and an acyclic clearance of ten 1.067 m high hurdles. According to Bruggemman [1], the high hurdle event can be divided into the following phases: approach run to the first hurdle, clearance of the hurdles and the rhythm between hurdles, and run-out from the last hurdle to the finishing line. Therefore, a proper hurdling technique is a complicated combination of various running and jumping kinematics [2]. Additionally the hurdler must show a high level of sprinting skill, excellent flexibility in the hip joint, coordination, balance, dynamic perception, elastic power, and a high level of technical knowledge [3,4]. Thus, athletes, coaches, and professionals are constantly looking for opportunities to improve the high hurdle

performance, focusing on hurdling technique with particular emphasis on the kinematics and kinetics analysis. During the last three decades, there has been a considerable amount of references concerning the analysis of hurdling technique at di fferent levels in order to improve performance [5–11].

One of the key elements that defines a competitive result in high hurdles is the hurdle clearance technique [11–17]. When clearing a hurdle, the loss of horizontal velocity should be minimized. This was confirmed by Amara et al. [17] and Coh et al. [18], who based on their hurdle clearance analyses, claimed that horizontal velocity is one of the most crucial factors, therefore losing it should be minimized; if not, the running time will be reduced. Additionally for the fastest possible and biomechanically e ffective clearance of the hurdle, the athlete's take-o ff distance and landing distance are essential. Furthermore, Salo and Grimshaw [19] determined the optimal ratio for an e fficient hurdle clearance. The ratio applies to the dependency between the take-o ff of the trial leg and the landing of the lead leg and should be 60:40 in flight distance. The hurdle clearance depends on other factors, especially those that define the movement trajectory of the center of mass (COM). The correct positioning of these two points determines the optimal flight trajectory of the COM, which is reflected in the flight time, which should be as short as possible [5,9,12,20]. According to Coh et al. [18] and Bubaj et al. [21] these two situations is a prerequisite for an optimal flight path of the center of mass (COM). This optimal path results in a shorter flight time. In addition to the correct position, the kinematic–dynamic structure of the take-o ff and landing are important, as they directly a ffect the speed of hurdle clearance [7,10,16,22,23]. To sum up the above considerations after Lopez et al. [24], Li et al. [22], Park et al. [25], and Amara et al. [17], the main criteria of an optimal hurdle clearance technique include horizontal velocity, height of COM at take-o ff, velocity of the trail-leg, flight time, height of COM at landing, and contact time.

Over the years, with the development of technology, the ability to record and film competitions in track and field has increased significantly. There has been a considerable amount of biomechanical data concerning the kinematic analysis of hurdle races at a high level of performance such as the Olympic Games, World Championships, or international meetings [24–29]. These analyses of the specialized video recording are related to the technical aspects of single event observations where competition stress and adrenaline are imposed on athletes. There has been a limited number of studies where obtaining the kinematic parameters of 110-m male hurdlers on the basis of video techniques analyses has been carried out on two consecutive races with the same competitors–hurdlers. Therefore, researchers use various video recordings in their analyses, although sometimes there are methodological di fferences in data collection processes. A similar procedure was used for the analysis of hurdle races of Colin Jackson and Dayron Robles, who set high standards in this athletic discipline. They were both world record holders in their 110 m high hurdle race careers and won medals at every major international competition. Colin Jackson set the world record in the 60 m hurdle race in 1993 in Sindelfingen (Germany) with a time of 7.30 s. A year later, he improved the world record in the 110 m hurdles with a time of 12.91 s, still considered the seventh-best time in the history of this athletic discipline. Dayron Robles also improved the world record in the 110 m hurdle race (12.87 s) in 2008 in Ostrava (Czech Republic), which is considered to be the second-best result of all time in high hurdle races.

These studies were conducted to analyze comparable data held by the Laboratory for Movement Control of the Institute of Sport, Faculty of Sport in Ljubljana. Biomechanical measurements of both athletes were performed at di fferent times, but under comparable conditions with similar measurement technologies. In both cases, a kinematic analysis of the fifth hurdle clearance technique was used. High standards of biomechanical measurements were taken into account, thus ensuring the high objectivity of the obtained results. We are aware that the study would have been even more valuable had we been able to analyze a greater number of obstacle clearances, but this was not possible due to organizational and technical constraints. The main aim of the study was to identify, analyze, and compare the essential kinematic parameters of the hurdle clearance technique at hurdle 5 of two athletes who have set the highest standards of biomechanical rationality of hurdle clearance in 110 m high hurdle races.

#### **2. Materials and Methods**
