A BIOMECHANICAL ANALYSIS OF THE LONG JUMP By Brian McLean In the following text Dr. Brian McLean of the Biomechanics Department at the Australian Institute of Sport, Canberra, presents a biomechanical analysis of some long jump performances in an investigation conducted during the 1994 Australian track and field season. The author outlines the rationale behind the choice of the parameters for the analysis and provides guidelines for the interpretation of the data. Reprinted with permission from Modern Athlete and Coach. Biomechanical analysis of long jump technique can help the individual athlete and coach to pinpoint weaknesses in the technique and sometimes the physical qualities that influence the athlete’s current performance level. Analysis in the laboratory or the field, using force plates and high speed cinematography, provides a comprehensive description of the athletes technique, and many such studies have provided a good understanding of the mechanics of the long jump. (Hay et al. 1987, Ramey, 1970). However, this type of analysis is expensive and the time period and human resources required to process the data often means that the service is limited to only few athletes. Measuring parameters that can be more readily obtained has the advantage of allowing analysis to be conducted in the field during competition and thus being available to a larger number of athletes. In recent years biomechanical analyses at major competitions throughout the world have provided information on selected biomechanical parameters characterizing individual athletic performances. In an effort to complement the laboratory testing that occurs for Australia’s elite long jumpers, the Biomechanics Department at the MS in Canberra, provided biomechanical analysis of the first Grand Prix long jump event of the 1994 season occurring in Canberra and for the long jump final at the 1994 National Championships in Sydney. The testing aimed to analyze every trial for each competitor. The following report outlines the rationale behind the choice of parameters chosen for the analysis and provides me guidelines for interpreting the data obtained. Sample results for both men and women are included. THE PARAMETERS Hay (1973) states that the distance an athlete jumps can be broken into three lesser distances. These are: 1. The horizontal distance between the front edge of the take-off board and the athlete’s centre of gravity at the instant of takeoff; i.e. the takeoff distance. 2. The horizontal distance that the athlete’s centre of gravity travels in the air; i.e. the flight distance, and 3. The horizontal distance between the athlete’s centre of gravity and the mark which is ultimately measured at the instant of touchdown; i.e. the landing distance. The takeoff distance is a function of the accuracy with which the athlete places the foot on the takeoff board, the build and body position at the instant of the takeoff (Hay, 1973). If an athlete has a reasonably consistent body position at the takeoff, since the build will not change, the largest influence on the takeoff distance will be the toe to board distance at the take-off. As this distance is relatively easy to measure, this parameter was chosen for analysis. Many investigators have shown that the parameter that has the largest influence on flight distance is the horizontal velocity at takeoff (Nixdorf and Bruggeman, 1990). This velocity is determined by the run-up speed and any speed losses that occur in preparing for the takeoff and during the takeoff. Approach speed during the run-up and in the last few strides prior to the takeoff can be easily measured in the field. The average velocity from 11m to 6m from the takeoff board and 6m to 1m from the board are frequently measured in competition, and therefore there is much data for comparison. Consequently, these average velocities were measured in this project. Horizontal speed losses during the takeoff are related to the support time during the takeoff (Nixdorf and Bruggeman, 1990). Longer contact times are associated with greater horizontal speed losses. However, loss of horizontal speed can also be (although not always) associated with increases in vertical velocity during the takeoff (Nixdorf and Bruggeman, 1990). Consequently, by knowing contact time during the takeoff, in conjunction with approach speed and distance jumped, an assessment can be made of the main factors occurring during the takeoff. Contact times during the takeoff were measured to complement the information provided by approach speed. Jump distance was also recorded. THE RESULTS Sample data for two male and two female athletes are provided. Toe to board distance is reported as positive if behind the board (legal) and as negative if over the board (foul). However, the mean foot to board distance for each athlete is the absolute mean, i.e. positive and negative values were averaged as if they were all positive. Averaging positive and negative distances would not give a useful representation of the foot to board distance as it may average to a small value when the distances, both positive and negative, may in fact be large. Mean data for approach velocity and contact time for the 1994 National Championships (female only) and the 1994 Canberra Grand Prix and comparative data from the Seoul Olympics are also provided. INTERPRETATION OF THE DATA Approach speed has been shown to be one of the most influential factors influencing the jump distance. Generally, the higher the approach speed the greater the jump. Comparison of an individual’s approach speed with that of other published results (see comparative data) will give an indication of the athlete’s current potential. In addition, the relative speeds between 11m to 6m and 6m to 1m may give an indication of how well the athlete is able to control their velocity during the run-up. A substantial decrease in velocity in the second interval, when compared to the first, may indicate that the athlete is over preparing for the takeoff by adjusting the stride pattern excessively approaching the board. Or the athlete may be slowing rapidly in an attempt to get into position for the take-off or trying to correct in order to target the board. Female Athlete B displays a large velocity decrease in the second interval. Notice that for the two trials where the largest velocity decreases occurred (trials 1 and 4), one resulted in a foul and the other in a poor jump. The mean data for both men and women at Seoul indicates that the best athletes generally do not have a substantial drop off in velocity over the last 11 metres. However, approach speed is not the only factor affecting performance. Technique is also important and becomes increasingly so as the approach velocity becomes faster and as the jump performance increases. Notice that for the women medalists in the Seoul Olympics, the highest approach speed did not produce the best performance. The ground contact times during the takeoff are also related to the approach velocity. A faster approach velocity and therefore takeoff speed will tend to lower contact times (Nigg, 1974). Contact times may also give an indication of the amount of loss of horizontal velocity during the takeoff. Generally, the longer the contact time the greater is the loss of horizontal velocity (Nixdorf and Bruggeman, 1990). Further, there is a relationship between the loss of horizontal velocity and the increase in vertical velocity (Nixdorf and Bruggeman, 1990): The larger the loss of horizontal velocity the larger the increase in vertical velocity. Therefore, contact times can give an indication of how much vertical velocity the athlete generates at the takeoff, and it is the vertical velocity at the takeoff which determines the height of the jump. However, if an athlete is weak and cannot tolerate the loads imposed in the takeoff, a long contact time may mean that the athlete generates only a small vertical velocity. Contact times need to be interpreted in conjunction with the approach velocity and the jump distance. For example, a short contact time may indicate that the athlete is not generating much height off the board. However, if the approach velocity is very high, a shorter than average contact time may still produce a reasonable vertical component of velocity and therefore a good jump distance. A high approach velocity and a long contact time producing a poor jump distance would suggest that the athlete is not getting good height off the board and is either technically poor in the takeoff or too weak to accept the takeoff loads. Male athlete A showed a very long contact time, in conjunction with reasonable approach speed and some above average jump distances. The long contact times most probably reflect the generation of vertical velocity during take-off, but may also indicate a lowered ability to accept the eccentric take-off loads. The athlete’s performance in a series of drop jump tests would assist in determining his ability to accept high eccentric loads. Analysis of the toe to board distance over an athlete’s six jumps can be diagnostic of the athlete’s run-up technique (Hay 1993). There are two parameters to consider when assessing the toe to board distance. These are the number of accurate jumps out of six, i.e. how many were not fouls, and the mean absolute distance of the toe to the takeoff board. These two parameters need to be considered together when interpreting this data and different technique problems can be highlighted from the relative magnitude of these parameters. Consider an example where the data shows that an athlete is highly accurate having only one foul jump out of six, but the average toe to board distance is large. This would suggest that the athlete has a consistent run-up pattern that brings the foot into a similar position relative to the takeoff board during each approach run. However, the high average distance from the board shows that the athlete is losing a lot of distance in the jump. This pattern is displayed by Female Athlete A. Since the run up pattern is consistent, moving the start further forward may decrease the toe to board distance, thus improving the jump distance. If, on the other hand, the athlete is very inaccurate, say getting five fouls out of six and the mean toe to board distance is large, this would suggest that the start mark needs moving back. Another athlete may have three fouls out of six and a large absolute mean toe to board distance. This would indicate that the athlete is sometimes over and sometimes behind the board and often by a considerable distance. This result suggests that the stride pattern in the run-up is not consistent. The toe to board distances of Male Athlete B suggests this problem. Specific drills to correct this may be required. When assessing the long jump run-up technique, the best result an athlete could achieve would be a very accurate takeoff with no fouls registered, in conjunction with a very small toe to board distance. Wind conditions should also be taken into account when assessing the run-up technique. Data gathered when there are gusting variable conditions may suggest a technique problem not seen when the data is collected in still conditions. If the athlete has a good run-up technique in still conditions but it deteriorates markedly in windy conditions, the athlete may need to work on this shortcoming when the opportunity arises to train in adverse conditions. CONCLUSION The biomechanical analysis outlined in this report highlights the usefulness of measuring simple biomechanical parameters during competition to assess the long jump technique. Although the parameters measured to do not provide a complete biomechanical characterization of the long jump technique, they have the advantage of being easy to collect and relatively quick to analyze. This type of analysis can assist the coach and athlete diagnose weaknesses in the long jump technique and make some assessment of the athletes current level of physical ability.
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