TECHNICAL FEATURES OF TAKE-OFF OF FEMALE LONG JUMPERS OF DIFFERENT SKILL LEVELS

O.B. Nemtsev, professor, Dr.Hab.
N.A. Nemtseva, associate professor, Ph.D.
S.M. Sukhanov, associate professor, Ph.D.
Adyghe State University, Maikop
A.V. Lytkin
Kuban State Technological University, Krasnodar
S.O. Parfenova
Maikop State Technological University, Maikop

Keywords: long jump, contact time, take-off speed, take-off angle.

Introduction. The long jump technique of female athletes was investigated by many authors [‎‎6, ‎7 et al.]. At the same time, quantitative indicators of the take-off technique of female long jumpers with different skill levels, as well as the relations between them remain ambiguous. Meanwhile, knowing the specifics of the technique of female long jumpers of different skill levels we could judge the dynamics in the growth of sports skills and therefore make a well-founded plan of training process for athletes of different skill levels. In this regard, the purpose of the study was to compare the take-off technique indicators of female long jumpers of different skill levels.

Materials and methods. Video recording of a long jump competition of ten female long jumpers and eleven female all-rounders was conducted at the Winter Championship of the Southern Federal District of Russia in 2014. The competition results were corrected according to the distance from the toe of the supporting leg to the take-off line. The characteristics of the best attempts of all athletes (subject to correction) were considered. The corrected results were ranked and the female athletes were divided into the following groups: group "A" (ten athletes with the best results: 21,3 ± 3,9 years old, corrected results 5.85 ± 0.24 m) and group "B" (eleven athletes with the results from fifteenth to twenty-first: 18,1 ± 2,8 years old, corrected results 5,19 ± 0,24 m). There was no available data on height and weight of the examined athletes.

The video was recorded using a digital camera Casio EX-ZR700 with the frequency of 240 Hz. The two-dimensional video analysis was performed using the software SkillSpector (version 1.3.2). There were defined the following technical characteristics: resultant take-off speed, horizontal and vertical take-off speed (determined by the speed of the common center of gravity (CCG), take-off angle (the angle between the resulting and the horizontal speed of the CCG), the angle of the supporting leg's knee joint in the moment of contact of the support and the value of knee flexion during the take-off period (the difference between the knee joint angle in the phase of contact with the ground and the smallest knee joint for the ground contact time), the distance from the horizontal projection of the CCG to the heel of the supporting leg in the moment of the ground contact, the CCG height at the moment of the ground contact and take-off, ground contact time.

The data were smoothed and filtered using the fifth-order spline filter. The significance of the differences in the compared parameters was determined using a one-way analysis of variance (ANOVA). The correlation ratio between the indices of the examined technique was assessed using a correlation analysis (Bravais-Pearson correlation coefficient).

Results of the study. As expected, significantly bigger values of the take-off speed and its horizontal component were reported in the group with the best sports results (Table 1, p <0,01). Averages of the vertical component of the take-off speed in group "A" were higher than those in group "B" by 10.8%, but the significant variation of the characteristics in both of the groups (variation coefficients 12.3 and 12.8%, respectively) did not enable us to consider these differences significant (p > 0,05). In addition, only insignificant differences were found for the two groups of athletes between the indices of the take-off angle, the knee joint angle of the supporting leg at the time of the track contact, the value of change of the knee joint angle during take-off, the distance from the horizontal projection of the CCG to the heel of the supporting leg in the moment of the ground contact and the height of the CCG at the moment of the ground contact and take-off (p > 0,05). Meanwhile, as seen from the study, more skilled jumpers perform their take-off significantly faster than their less skilled counterparts: they had significantly smaller contact time values (p <0,05). Moreover, a strong negative correlation between the contact time and the result (r = - 0,74) was found in the group of more skilled athletes, while the correlation between these indices in the group of less skilled athletes was weak (r = – 0,37).
Interestingly, a strong positive correlation was found between the vertical take-off speed and the take-off angle in both of the groups of athletes (Fig. 1). At the same time, an average negative correlation was detected between the horizontal take-off speed and the take-off angle in group "B" (r = - 0,54), and a weak positive correlation - in group "A" (r = 0,41). This suggests that the take-off angle in athletes of the studied skill level to the greatest extent is determined by the take-off vertical speed. Possibly athletes with results from 4.70 to 5.58 m (Group "B") have difficulty with taking off at the optimal angle with increasing horizontal speed of the take-off. In group "A" a medium strength correlation (r = 0,65) was also discovered between the indices of the horizontal and vertical speed of the take-off, confirming that athletes of this group can successfully coordinate their efforts in horizontal and vertical directions. Group "B" athletes showed a weak negative correlation between these indices (r = – 0,27).

Table 1. Take-off technical characteristics (arithmetic mean ± standard deviation) of female long jumpers of different skill levels

* Here are shown the calculated values of F-test according to the univariate analysis of variance. The boundary values of F-test are as follows: F_0,05 = 4,38, F_0,01 = 8,18, F_0,001 = 15,08.

It should, however, be taken into account that a small number of subjects involved in this study determines the significant width of confidence intervals of some of the calculated correlation coefficients. Thus, if for the correlation coefficient of 0.96 dependency between the angle of take-off and the vertical speed of the CCG in female athletes of group "A" the 95% confidence interval is (according to [2]) from 0.84 to 0.99 (in other words, the correlation of the mentioned indices in general is more likely to remain strong), then the same confidence interval of the correlation coefficient of 0.65 dependency between the indices of the horizontal and vertical speed of take-off in the same group of athletes ranges from 0.03 to 0.91 (in other words, in general totality the studied dependence can be both strong and lacking). So it prevents from attributing the found dependencies to the general totality of female athletes with corresponding skill levels and determines the importance of further researches in this area.

Fig. 1. Correlation between vertical speed and take-off angle indices of athletes in groups "A" and "B"

The results of the present study confirm the findings of a number of authors (having different degrees of proof) on the fact that improvement of sports skills promotes a decrease of the take-off contact time in long jumps [‎1, ‎4 et al.]. The reduced contact time during a take-off in long jumps must be typical for any case of increase of the horizontal speed of movement of an athlete. Thus, there is evidence of a decrease in contact time in take-off with the increasing run-up length and, consequently, an increase of the horizontal speed of the CCG [‎3, ‎5]. However, if in the first case [3], the authors show that the position of the supporting leg and its segments in the moment of contact with the ground remains the same with the increasing takeoff run-up length, in the work [5] a significant increase is marked in the knee joint angle and the value of knee flexion during the ground contact time, as well as the distance from the horizontal projection of the CCG to the heel of the supporting leg in the moment of contacting the ground by increasing the takeoff run-up length (and the horizontal speed of the CCG). The dependencies of the horizontal and vertical components of the take-off speed as well as the take-off angle are described by different researchers in different ways. Thus, for example, there was noted [6] an increase in the vertical take-off speed in the finalists of the World Student Games due to reduction of the horizontal speed. Another study [4] showed that the vertical take-off speed in the long jump in the decathletes who have better results (and the horizontal take-off speed), is significantly higher than that in their less skilled counterparts. The present study also provides original data on the interrelations between the most important indices of the take-off technique in long jumps (horizontal and vertical speed of the CCG at the moment of take-off from the ground, the angle of take-off) in female jumpers of different skill levels, which are both of different strength and orientation.
Conclusion. Thus, female long jumpers, who have results from 4.70 to 5.58 m (group "B") and from 5.62 to 6.31 m (group "A"), do not differ significantly in characteristics of the position of the supporting leg segments during take-off. Nevertheless, female jumpers with lower results perform a take-off significantly longer. Athletes of both of the studied groups have a strong dependence of the take-off angle on the vertical take-off speed. Moreover, if the athletes with the higher skill level are good in coordination of their efforts in horizontal and vertical directions (average positive correlation between the parameters of horizontal and vertical speed of the CCG), in the athletes with the lower skill level the increasing horizontal speed leads to a decrease in the take-off angle (average negative correlation).

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Corresponding author: oleg.nemtsev@mail.ru

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