73 Kinematic analysis of the hurdle clearance techniques and the first stride after clearance in 110m sprint hurdles: Comparative study under real competition between elite hurdles specialists and elite decathletes * Dr/ Mahmoud Attia Bakhet Ali ** Dr/ Said Mohamed ben Ahmed Abstract The aim of this study was to compare the kinematics of hurdle clearance and the first stride inter-hurdles, under real competition between Elite Hurdles Specialists (EHS) and Elite Decathletes (ED). Materials and methods: The study was carried out on 20 male athletes (10 EHS in 110m hurdles sprint and 10 ED). All subjects were qualified for the semi-finals and finals of Russian Outdoor Track and Field, National Championships and Moscow Athletics Championship (2009). Kinematic parameters were determined by using a video kinematic analyzer. The indices of spatial and temporal interaction with the support, as well as, the angular parameters of motion and height of the body gravity center «BGC», for some various postures, were determined. Results: EHS were characterized by a faster hurdle crossing (p <0.01), a smaller stride length over the hurdle (P <0.05), and a shorter supporting phase of the first stride post-hurdle (p <0.01). The flight curve of the «BGC» was higher in ED than EHS (p<0.01). EHS attack the hedge with a lead leg knee significantly more flexed (p<0.001) and after crossing the hurdle, they regain the contact of the ground with lead leg more flexed at the hip level (p<0.01), a trunk more inclined forward (p <0.01) and positioning angle of the supporting leg relatively smaller (p<0.05). Conclusion: EHS were distinguished by maintaining efficient sprinting mechanics over the hurdles * Physical education department Faculty of education King Faisal university Saudi Arabia ** Physical education department Faculty of education King Faisal university Saudi Arabia - Russian Research Laboratory Sports Performance Optimization, University of Moscow State Mining, Moscow, Russian Federation.
74 enabling them to develop optimal velocities between the hurdles. This was reflected in: shorter impulse time, more important reduction of braking forces at the moment of landing and touchdown, more fluid and quick resumption of optimal speed between hurdles. Key words: Kinematics, hurdle clearance, first interhurdles stride, hurdlers, decathletes. Introduction Unlike the flat sprint where the structure of the stride, in terms of amplitude or frequency, is not subject to any important external constraint, the hurdle event is a model of repetitive activity, involving very important spatiotemporal imperatives (Babić, Harasin, and Dizdar, 2007). Proper hurdling technique is a complicated combination of various running and jumping kinematics (Bollschweiler, 2008). Among the three outdoor hurdle events currently being run at the international level the high hurdles sprint is the most demanding track and field events (Salo & Grimshaw, 1997). Thus, athletes, coaches, and researchers have sought to improve hurdle performance by placing more emphasis on the kinematics analyzing of hurdling techniques. Over the years, there has been a considerable amount of biomechanical literature concerning the kinematic analysis of hurdle clearance at different levels of performance, in male and female athletes (Mann, and Herman, 1985; Brüggemann, 1990; McDonald and Dapena, 1991; Salo, 1997; Bollschweiler, 2008). However, there has been little information comparing the various characteristics of movements, between the toplevel hurdles specialists and high level combined events athletes. Moreover, the analysis of the specialized literature shows that largest part of studies related to the technical aspects of hurdles sprint observations are performed during training conditions or derived primarily from special conditions arranged in advance, and not during actual competitions or race pressure. It is however, difficult to simulate actual competitive race conditions during such arranged measures. It is also quite likely that the athlete will concentrate on official event and then, run slightly
75 faster during the competition, than it is under other practice conditions (Salo & Grimshaw, 1997). This is due notably, to factors such as adrenaline and to the fact that, in a meet, you only have to run it once. Therefore, the aim of this study is to provide descriptive kinematics of some biomechanical factors involved in the hurdle sprint techniques, in order to identify on the basis of a comparative analysis, common components and specific distinctive technical elements of Hurdles experts and Decathletes. The study was carried under real competitive practice situation, involving hurdles specialists and decathletes. Method Participants Data are collected over 20 elite russian athletes divided into 10 male elite hurdles specialists «EHS» (age: 20,91 ± 2,2 years, body mass: mass 76,90 ± 6,96 kg, height: 1,85 ± 0,05 cm), and 10 male elite decathletes «ED» (age: 20.83 ± 2.17 years, body mass: mass 87,70 ± 6,85 kg, height: 1.91 ± 0,03 cm). Subjects were filmed at the semi-final and final of the Russian Outdoor Track and Field National Championship, and Moscow athletics championship. All stages were carried out in 2009, in warm temperature around 26-27, and a wind velocity of 0.0m/s-1.The protocol of this study was determined by All-Russia Athletic Federation (ARAF) to be exempt from a need for informed consent since the event is considered public domain Parameters Kinematic parameters of the 110m hurdles sprint technique were defined by a kinematic analysis of motion performed using a high speed camera «Arriflex SR-II, Germany» equipped with a telephoto lens (Angenieux 10-150 mm, France). This later was placed perpendicular to the axis of the runway at the fifth hurdle level to obtain a sagittal view of the hurdler as the athletes clear the obstacle (Hunter and Bushnell, 2006). Frequency of filming was 100 f/s in an area that allowed the taking of a view to a whole phase of hurdle clearance, including a touchdown phase and entire cycle of the first stride after the filmed hurdle. Each recorded film frame was analyzed using a kinematic analyzer of motion (REGAVI software, version 2.57, 2004).
76 The distance between camera and the filmed target was 11m, whilst the height of its attachment was 1.27 m, and remained unchanged during the recordings. Statistical Procedures The statistical analysis of the results was carried out using SPSS 16.01. Results are presented as mean ± SD. Differences between each groups were compared with the Student test for independent samples. The level of correlation of the studied parameters with the achieved performance was examined by the simple correlation of Bravais Pearson. The significance threshold was fixed at P< 0.05. Results Spatial and temporal data Performances of 110m hurdles sprint achieved by elite huddles specialists were significantly better than those of elite decathletes (p <0.001). The relative values were respectively 14.78 ± 0.608s and 16.06 ± 0.666s (Table 1). The comparison of kinematic parameters between ED and EHS revealed that the amplitude of the stride over the hurdle is significantly greater in decathletes. This larger hurdle step length coincides with larger takeoff. This is expressed in the attack area, clearly, the significant discrepancy in the distance from the take-off point to the hurdle which is equal to 2.16± 0.12m in ED and 1.95± 0.19m in EHS (p<0.05). Whereas, the distance from the hedge to the touchdown point, after clearance was not statically significant in all subjects. Average hurdle stride was 3,60± 0,17m in EHS and 3,84±0,267m in ED. The take-off distance was respectively 1,95± 0,19m and 2,16±0,125m, which represents 54.16% and 56.25% of the total hurdle stride length. The landing distance was 1,66±0,16m in EHS and 1,68±0,233m in ED, which is between 45.83% and 43.75% of the total hurdle stride length (Figure 1, Figure 2). Thereby, EHS were characterized by a less extensive hurdle clearance stride (3.60±0.167m vs. 3.84±0.267 m, P<0.05), a shorter flight time over the hurdle (0.37±0.03 vs 0.41±0,047, p<0.01), and a smaller support phase of the first step inter-hurdle (0.102± 0.013s vs 0.128±0.018s, p<0.01). Whereas, except the moment of contact of the supporting leg with the ground before the attack on the hedge,
77 the flight curve of the BGC in ED was higher than that in EHS (p<0.01). Body position above the hurdle was also higher in ED than EHS; distance was respectively 1.45±0.041m and 1.29±0.03m (Figure3). Table (1) Spatial and temporal parameters of hurdle clearance and the first stride post hurdle in Elite Hurdlers Specialists and Elite Decathletes Parameter ESH (n=10) ED (n=10) Stride length over the hurdle (m) 3,60± 0,17 3,84±0,267* Flight time over the hurdle (s) 0,37±0,03 0,41±0,047* Distance from the point of the take-off 1,95± 0,19 2,16±0,125 in front of the hurdle(m) Distance from the hedge to the touch-down point behind the hurdle (landing point) (m) 1,66±0,16 1,68±0,233 Amplitude of the first stride post-hurdle (m) 1,56±0,1 1,70±0,107* Support time of the first stride post-hurdle (s) 0,102±0,01 0,128±0,018* Flight time of the first stride post-hurdle (s) 0,076±0,016 0,073±0,017 Height of the BGC at the time of 1,03±0,04 1,04±0,05 contact of the support leg with the ground, before the hedge attack (m) Height of the BGC at the moment of 1,15±0,05 1,26±0,07** take-off while attacking the hedge (m) Maximum height of the BGC when 1,29±0,03 1,45±0,04** crossing the hedge (m) Height of the BGC at the moment of landing (m) 1,17±0,03 1,24±0,06* Height of BGC at the impulse of the 1,07±0,02 1,13±0,05* first stride post-hurdle (m) Performances (s) 14,78±0,608 16,06±0,666** * p< 0.05 ** p< 0.001
78 Table (2) Angular variations at the attack and landing phases and at the first stride post-hurdle in Elite Hurdle Specialists and Elite Decathletes Phase Member Angle ( ) ESH (n=10) ED (n=10) Attack Landing The first stride posthurdle Support leg Ankle 144,3±8,3 140,5±6,57 Knee 164,6±7,93 165,3±6,58 Hip 175,3±10,11 173,8±8,94 Impulsion 69,0±4,35 68,9±3,48 Knee 70,8±7,79 97,2±13,89** Attack leg Trunk Inclination to the 22,2±5,59 22,2±6,76 vertical Support Ankle 138,7±7,89 139.1±5.42 leg Knee 171,3±8,25 176,2±9,29 Hip 134,6±10,89 152,9±14,94* Positioning angle 73,2±2,82 77,1±4,07* Attack Knee 40,9±14,81 48,7±19,12 leg Trunk Inclination to the 28,8±7,87 16,6±10,45* vertical Support Ankle 140,6±7,23 141,2±9,18 leg Knee 163,6±5,3 161,5±6,7 Hip 194,5±5,64 196,9±11,66 Impulsion 60,5±4,04 57,0±2,26 * Lead leg Knee 118,4±10,23 122,2±13,86 Trunk Inclination to the 11,14±3,84 8,7±7,29 vertical * p< 0.05 ** p< 0.001 Figure 2. Kinematic parameters of the stride after clearance at elite 5th hurdle clearance and the first hurdlers specialists
79 1 6.6 22. 2 8. 7-16.3 48.7 9 7.2 7 7.1 17 6.2 13 9.1 2.1 6 m 1 61.5 1.13 m 68.9 1 40. 5 1 22.2 1.24 m 1.45 m 1,26 m 1,04m 165.3 1 96.9 1 52. 9 1 73.8 57.0 1 41.2 1.6 8 m A tta ck a re a d is ta n ce L a n d in g a re a d ista n ce 3.8 4 m C le a ra n c e s tr i d e 1.70 m l en gh L e n g h o f t h e fi rs t s t r id e in t e r - h u rd le Figure 2. Kinematic parameters of the 5th hurdle clearance and the first stride after clearance at elite decathletes. Y 1.60 ED EHS 3 1.40 2 1.20 4 5 1 1.00 80 0 Figure3. Elite Hurdlers Specialists and Elite Decathletes flight curve of the BGC at the hurdle clearance and the first stride after clearance. The study of intercorrelations has shown that performance in 110m hurdles in both groups was positively correlated with the time of hurdle crossing (EHS: r = 0.74, p<0.01; ED: r=0.63, p<0.05) and with the duration of the support phase of the first step post-hurdle (EHS: r=0.91, p<0.001; ED: r= 0.73, p<0.01). Angular Kinematics 1.07m 1.13m 1.24m 1.17m 1.29m 1.45m 1.15m 20 1,26m 40 1.03m 60 1,04m Hight of the BGC 1.80 Distance X At the moment of the hurdle attack, no significant differences were observed between the two groups in term of angular kinematics of the supporting leg, the hip attack leg, the body inclination, and the impulsion. However, when negotiating the barrier, the EHS showed a lead leg knee flexion significantly more than that of decathletes (p<0.001) (Table2). During this phase, trunk slope forward influences significantly the achieved performance (ESH: r=- 0.7; p<0.05; ED: r=- 0.63; p<0.05). However, at the landing phase, EHS regain contact on the
80 ground, with trail leg more flexed at the hip level, a more sloping trunk forward by report to vertical, and a smaller positioning angle of the trail leg (p<0.05 for all). During this phase, the performance of EHS on 110 m hurdles sprint is positively correlated with the hip opening (r=0.66, p<0.05). Nevertheless, the sequence of the first stride inter-hurdle is made with no significant angular variation in all studied subjects, except that of the propulsion, which is significantly more open in EHS (p<0.05) (Table 2). Discussion According to the collected data, we can say that improving the performance in hurdles sprint involves a number reduction of spatiotemporal parameters. This means, in the sense that Bernstein (1967) intends a degrees freedom reduction of system. This is expressed in fact, by the training of invariants of this activity spatio-temporally organized. Nevertheless, and contrary to the findings of Beaubaton (1983), the present study shows that the improvement of the performance in 110m hurdles sprint event is dependent on spatial as well as temporal parameters. The diversity of these parameters, that Konig (1989) characterizes as a phase or a part of the movement's structure phase, are linked with the problem solving of specific force potential and its development. On this point, the vertical force components in the support phase are of great importance, especially during the crossing of each hurdle (Bubanj et al., 2008). However, during the translation of body segments we can distinguish invariable and common characteristics. Whose disclosure would be essential both for the determination of universal mechanisms of the temporal and spatial movements organization of hurdlers, and then for solving problems related to the presence of the obstacle (Mclean, 1994). This is of particular importance in athletic combined events, since the representatives of this athletic event are constrained to develop their technical skills in several athletic specialties at once, while the training efforts of hurdlers are focused only on the improvement of hurdling skills, the refining of hurdles sprint mechanics, and the
81 establishing of general sprint conditioning (and even the distribution of energy throughout the race). The resolution of such tasks would be even more successful when the general mechanisms constituting the basis of such combined events or distinct technical elements of the same discipline will be appropriately studied. Our results noted also the importance of increasing the sprint rhythm to improve the 110m sprint hurdlers performance. This means, the rhythm of running between and over the hurdles needs to be matched with the technique and agility of the runner. Agility itself depends on several factors, especially those which describe the launching phase in front of hurdle, the path line of the BGC and the landing after the flight over the hurdle (Bubanj et al., 2008). Running speed could be increased also by the optimization of support and flight time (Dapena, 1991, Milan et al. 2004) and by reducing the amortization time (Milan, 2003). It is in qualitative mastery of the amortization phases that during the international championships, we distinguish very well today`s winners and future winners (Konig, 1989). Indeed, the aforementioned is of paramount importance in the high sprint hurdles where the amplitude of the stride is closely linked to the morphological characteristics of the athlete, the number of strides between the hurdles and the thrust angle (Susanka et al., 1988; Milan, 2003). The present study confirms these suggestions and shows also, that the EHS are distinguished from ED by shorter stride length over the hurdle, lower BGC flight curve and faster crossing technique. Thus, a fluency and agility to run over the hedge was significantly higher. Milan, C., Milan, Z., and Bojan (2004)) found that elite athletes with shorter hurdle clearance times had faster hurdle running times. According to McDonald and Dapena (1991), the criterion of an efficient hurdle clearance technique is the shortest possible time of the flight phase (hurdle clearance time) otherwise; the hurdler loses velocity in air. According to Bubanj et al. (2008), this condition is a very effective way to reduce the vertical
82 oscillations of the BGC since it allows the athlete to maintain a stable horizontal velocity and develop a consistent stride pattern. It is worthy to notice in this sense that our results determined under real competition support the findings of (Finch, Ariel, and McNichols, 2000) determined under experimental conditions in top-level hurdlers. Our results reveal also the existence of significant discrepancies between ED and EHS, regarding to the first stride post-hurdle. These divergences, confirmed by the positive correlation between the support phase duration of the first stride after the hurdle and the race performance, demonstrate in fact that the lowest values of these indices correspond to better performance. This could be explained by the necessity to minimizing the braking forces in order to maintain a constant horizontal velocity along the race (Finch et al., 2000) and enable a quick resumption of optimal speed between the hurdles. Indeed, it is notorious that, one of the most important characteristics of the effectiveness of the hurdles sprint techniques is the ability to maintain a high and constant running rhythm without losing balance, especially after crossing the hurdle at the touchdown moment (Hay, 1993), and the braking phase that must be as short as possible (Milan et al., 2004)). Moreover, a typical technical fault perceived, particularly among novice runners, is the considerable loss of speed after the touchdown which leads consequently to a considerable reducing of the horizontal velocity and amplitude of the first stride after the hedge (Kampmiller, Slamka & Vanderka, 1999; Bubanj et al., 2008). For this reason, it becomes clear that the optimal flight time in EHS, during the recovery stride (post-hurdle), reflects a more efficient running technique (Bubanj, 1997). This underline the finding of Li and Fu (2000) that the first stride after the hurdle is a crucial factor that determines whether or not the hurdle clearance technique is satisfactory. The comparative analysis of the angular kinematics also allowed revealing some general patterns of interaction with support. In fact, the EHS are distinguished by more pronounced trunk
83 slant forward when crossing the barrier particularly during the landing phase. This body posture, notably the trunk lean forward at landing phase, creates auspicious conditions for an active landing after clearing the hurdle, minimize the loss of speed mainly during the amortization phase, ensures easier forward locomotion (McDonald and Dapena, 1991) and allows to lower at an optimal level the BGC above the barrier (Bollschweiler, 2008). It should be also noted the more efficient movement of the attack leg of EHS notably at the moment of propulsion and attack of the hurdle. In fact, the smaller knee angle of the lead leg reduces its moment of inertia and contributes therefore to the higher energetic rotation of the hip at the moments of propulsion and the attack of the obstacle (Bubanj et al., 2008). According to Milan (2003) this action of the leading leg increases the value of the horizontal BGC speed of the athlete in clearing the hurdle. Conclusion The comparative kinematic study of the fifth hurdle clearance and the first stride post-hurdle of elite hurdlers specialists and elite decathletes allowed determining the common components and the specific distinctive technical elements of each group. By examining the kinematic particularities in the phases of launch, flight and landing, some of the most important parameters have been determined. It was found that EHS are distinguished from ED by: - Shorter flight time; - Shorter length stride over the hurdle; - Lower BGC trajectory; - More tilted trunk forward at the landing phase after clearance; - Shorter braking phase at landing; - More open propulsion angle at the attack moment in front of the hurdle and at the first stride inter-hurdle; - Shorter support time at the recovery stride after clearance. The results of our study showed that EHS are distinguished by more rational and efficient hurdling techniques which were expressed in the better outcome of the latter. Being an indicator of good hurdling efficiency, we think that the data collected during the official competition and the results shown by examining the specific features of linear and angular kinematics of the 110m hurdles sprint in EHS and ED could be useful firstly for the estimation of hurdling technics and secondly to give a clearer comprehension of hurdling
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