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Abstract:
Through Quantitative kinematic analysis this experiment compare two different vertical jump techniques. Six college-age students participated on this experiment. Each Subject performed one counter-movement vertical jump and one-drop jump. The aim of the experiment through the kinematic analysis was to examine the major body segments that involved during the two different jump techniques and moreover to give explanation for the dissimilarities if there are any. According on the statistical analysis there was no significant differences between the two jump techniques. On the other hand, through the average results, it can be supported that there was a variation between the two different jump techniques. However based on the high marked standard deviation (SD) the final suggestion was that any conclusion under these circumstances could be unreliable and inaccurate. Therefore a further and more accurate collection of data must be done in order to succeed an accurate and reliable kinematic analysis between the two different jump techniques.
Key words: quantitative kinematic analysis, compare, vertical jump, countermovement jump, and drop jump.
Introduction:
Nowadays vertical jumping has become one of the most essential training tasks and a method, which lead to the increasing of sport performance. Vertical jumping is though to be a complex and multidimensional action, which effected by numerous factors. One of the factors that vertical jumping effected is the technique that the performer will use to perform the vertical jump.
According on studies by Bosco and Komi (1979) vertical jump performance increases when there is an increasing of stretch loads. For example, during drop jumping, the height of the subsequent jump increases when there is an increase in drop height. This occurs only up to a point. There is a threshold at which the stretch load is too great and the organ reflex causes an inhibition of muscle contraction reducing the jump height attained (Gollhofer & Kyrolainen, 1991; Schmidtbleicher et al., 1988).
The aim of the experiment was to examine two different jump techniques. The comparison was between standing vertical jump (countermovement), and a rapid vertical jump after a drop jump. Kinematics analysis focused on the different variables between the two jump techniques. In detail, kinematics analysis focused on max angles flexions of key point joints (ankle, knee, hip), the time that max angles flexions occurred before takeoff, time of flight, time of peak height of CM, and vertical velocity at takeoff.
Method:
Subjects
Six healthy collegian students (age 20+ 2) performed two types of maximal-effort vertical jumps. It was asked from the subjects to wear a tight short during the period of data collection in order to succeed an accurate marking of the key angles of ankle, knee, and hip joints.
Procedure
The camera mounted on a stationary, rigid tripod pointing towards the center of the plane of motion. After the formation of the appropriate background (there must be a color contrast between the performer and the background, so to be clear the body segments that are going to be used for the digitizing), next step was to calibrate the plane of motion. Calibration procedure is essential for an accurate quantitative analysis. A six points coordinate digitizer was used to calibrate the plane of motion. The filming (for 1-2 s) of the 6 points coordinate digitizer provided a number of coordinates that after the calibration- were displayed on the computer software. After the end of pre-experiment procedures subjects was ready to perform their tasks.
Subjects performed vertical jumps following two different initial starting positions:
1) According to the first jump technique, subjects from a standing position performed a vertical jump after a
natural counter-movement (CMJ).
2) According to the second jump technique, subjects dropped from a 25cm box and performed a vertical jump as rapidly as possible (DJ).
Arms movement allowed during both vertical jump (CMJ), (DJ) techniques.
Equipment
A Sony TRV900E camera was used to film all the jumps. The film data were digitized using a target/ Apex high resolution video digitizing, Loughborough University innovation. Charwood dynamics computer software was used for the analysis of the data.
Results
Twelve, t-test between CMJ and DJ one for every digitized data took place in order to define the differences between the two techniques if there are any. Research hypothesis was that there are differences between CMJ and DJ. The statistical analysis was based on SPSS statistical computer software program.
Mean max ankle flexion (deg) during CMJ was 74.5 (SD: 4.5). In contrast, mean max ankle flexion (deg) during DJ was 75.1 (SD: 6.4). Additionally there was no significant difference at the max ankle flexion (deg) between CMJ and DJ since t-test outcome was 0.869>0.05 (Appendix C). Mean time (s) that max ankle flexion (deg) occurred before takeoff for CMJ was 0.20 (SD: 9.3) and for DJ was 0.16 (SD: 4.22). There was no significant difference between CMJ and DJ at the time (s) that max ankle flexion (deg) occurred before takeoff since t-test outcome was 0.231>0.05 (Appendix D). Mean max knee flexion (deg) for CMJ was 91.3 (SD: 22.2) and for DJ was 98 (SD: 14.4). There was no significant difference between CMJ and DJ at the max knee flexion (deg) since t-test outcome was 0.365>0.05 (Appendix E). Mean time (s) that max knee flexion (deg) occurred before takeoff for CMJ was 0.20 (SD: 9.11) and for DJ was 0.17 (SD: 3.44). There was no significant difference between CMJ and DJ at the time (s) that max knee flexion (deg) occurred before takeoff since t-test outcome was 0.348>0.05 (Appendix F). Mean max hip flexion (deg) for CMJ was 84 (SD: 25.9) and for DJ was 101.6 (SD: 15.4). At that point there was a significant difference between CMJ and DJ for max hip flexion (deg) since t-test outcome was 0.037<0.05 (Appendix G). Mean time (s) that max hip flexion (deg) occurred before takeoff for CMJ was 0.24 (SD: 9) and for DJ was 0.20 (SD: 4.88). There was no significant difference between CMJ and DJ at the time (s) that max hip flexion (deg) occurred before takeoff since t-test outcome was 0.166>0.05 (Appendix H). Mean angle (deg) at ankle at takeoff for CMJ was 93 (SD: 12.4) and for DJ was 101.8 (SD: 9.5). There was no significant difference between CMJ and DJ at angle (deg) of the ankle at takeoff since t-test outcome was 0.269>0.05 (Appendix I). Mean knee (deg) angle at takeoff for CMJ was 127.6 (SD: 22.3) and for DJ was 141.8 (SD: 14.6). There was no significant difference between CMJ and DJ for knee angle (deg) at takeoff since t-test outcome was 0.261>0.05 (Appendix J). Mean hip angle (deg) at takeoff for CMJ was 141.1 (SD: 6.6) and for DJ was 149.8 (SD: 12.3). There was no significant difference between CMJ and DJ for the hip angle (deg) at takeoff since t-test outcome was 0.065>0.05 (Appendix K). Mean time (s) of flight for CMJ was 0.65 (SD: 6.4) and for DJ was 0.61 (SD: 8.33). There was no significant difference between CMJ and DJ for the time (s) of flight since t-test outcome was 0.283>0.05 (Appendix L). Mean peak height of CM (s) for CMJ was 1.51 (SD: 0.14) and for DJ was 1.5 (SD: 0.17). There was no significant difference between CMJ and DJ for peak height of CM (s) since t-test outcome was 0.947>0.05 (Appendix M). The last digitized data that took place was the vertical velocity at takeoff (m/s). Mean vertical velocity at takeoff (m/s) for CMJ was 2.81 (SD: 0.43) and for DJ was 2.5 (SD: 0.47). Again there was no significant difference between CMJ and DJ for vertical velocity at take off (m/s) since t-test outcome was 0.076>0.05 (Appendix N).
Discussion
According on the statistical results there is no significant difference between CMJ and DJ techniques. The only significant difference was found at max hip flexion (deg). During digitizing procedure it was difficult to indicate the center of major joints (ankle, knee, and hip). As a result some of the data may be inaccurate, and that could be a good explanation for the oversize SD. Therefore the analysis (comparison) between CMJ and DJ will be based on the averages results (table 1).
Vertical jumping is a complex type of motion. Moreover, big and complicated muscle segments coordinate in order to achieve a strong and clear vertical jump. The major muscles that participate during vertical jumping are: a) the gastrocnemius muscle (ankle joint) and b) the quadriceps muscle (knee joint). Max ankle flexion (deg) before takeoff remains almost the same during CMJ and DJ. However the difference between CMJ and DJ on max flexion (deg) before takeoff start to enlarged moving from knee to hip joint (table 1). According on a recent research from Holcomb, W.R. et al. in 1996, during DJ there is an enhancing on the contribution of the muscles required to extend the ankle, knee, and hip compare to CMJ this was accomplished by modifying the range of motion (ROM) of the joints being emphasized during the down phase of DJ. This increases the flexion of the major joints while minimizing flexion of the other joints when absorbing the force of landing. Their final suggestion through their research was that DJ could increase the emphasis of movement on major joints.
The time of impact with the ground during DJ expected to be much lesser than it was during CMJ (that is the aim of DJ plyometric exercise-). As a sequence, the time needed from the subject to generate max ankle, knee, and hip flexions before takeoff (deg) during DJ was lesser than it was during CMJ. As a result, max ankle, knee, and hip flexion during DJ was closer to the takeoff phase than it was during the CMJ.
Based on the average results the time of flight during CMJ was greater than it was during DJ, moreover peak height of CM (s) during CMJ reached in 1.51 and during DJ reached in 1.50. There in no great difference on time of flight and vertical velocity at takeoff between the two jump techniques but according on the results it can be supported that the height of the CMJ was greater than it was for DJ. Several researches have been done on the interrelation between elasticity of the muscles and the energy that produced under different stretching techniques during vertical jumps. Asmussen, E and F. Bonde-Peterson in 1974 have been suggest that when the subjects jumped down from a height, more energy was made available for tautening the elastic components of the muscles. Therefore more energy could have been made useful for the jump. Another research from Bosco and Komi in 1979 suggests that vertical jump performance increases when there is an increasing of stretch loads. For example, during drop jumping, the height of the subsequent jump increases when there is an increase in drop height. Although, a research from Weston, J in 1994 based on the differences in selected biomechanical parameters during counter movement (CMJ) and drop (JD) jumps support the opposite. Twenty-five female basketball and volleyball athletes have been participate on the experiment. According on his findings peak jump height was similar during the two different jumps conditions. His suggestion was that the elastic component of the muscle played no role on the max jump height during DJ. As a result the height of jump was the same during CMJ and DJ. Total body vertical jumping is a multi-joint movement, which is some function of the combined impulse of all muscles participating in the movement. Several and complicated parameters involved during vertical jumping. As a result more and detailed researchers must take place in order to define if there is any interrelation between the elastic components of the muscles and the max height of vertical jumping.
Based on the results, the major factors that affect vertical jumping during CMJ and DJ, was the vertical velocity at takeoff and the time of flight. Through, time of flight a prediction of the jump height can be take place. Greater time of flight indicates higher vertical jumping. The major parameter, which, influence the height of jump according on the findings was the vertical velocity at takeoff (m/s). Height of the jump increased almost linearly in relation to vertical velocity. This relationship is based on the law of physics, which support that the greater the vertical velocity of an object the easier the object overcomes the law of gravity. According on the graph (Appendix O) there is a parallel relationship between vertical velocity at takeoff and time of flight. In details, an increase in vertical velocity at takeoff is followed by an increase on the time of flight. Furthermore, decrease in vertical velocity at takeoff followed by a decrease on time of flight. The above explanation supports that there is a relationship between height of jump and vertical velocity and is based on the fact that the height of the jump can be predicted through the time of flight.
Conclusion
To sum up, there are differences between CMJ and DJ. Greater max angles flexion for major joint (ankle, knee, hip) occurs during DJ. Max jump height seems to be unrelated with the muscles elasticity and therefore with the greater ankle, knee, and hip flexion. On the other hand according on the law of physics vertical velocity is the major component that influence the max height of the jump. Although, since total body vertical jumping influenced by a number of physiological parameter a deeper and more accurate research will help in order to define the differences between CMJ and DJ.
REFERENCES
Asmussen, E and Bonde-Petersen, F (1974). Storage of elastic energy in skeletal muscles in man. Acta Physiologica Scandanavica. Vol 91, pag 385-392.
Roger Bartlett, 1997. Introduction to sport biomechanics. Great Britain: E & FN Spon, an imprint of Chapman & Hall.
Bosco, C and Komi, P (1996). Potentiation of the mechanical behavior of the human skeletal muscle through pre-stretching. Acta Physiologica Scandanavica. Vol 106, pag 467-472.
Holcomb, W. R. et al. (1996). A biomechanical analysis of the vertical jump and three modified depth jumps. Journal of strength and conditioning research. Vol 10 (2), pag 83-88.
Weston. J, 1994. A study of biomechanical variables in the countermovement jump and the drop jump performed by female intercollegiate athletes [on line] available from: http://www.newtest.com/newpag/library/jump/eng/volleyba.html [accessed: 27-03-01]
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