How Can Sport Biomechanics Contribute to the Advance of World Record and Best Athletic Performance?

Transcription

1 Measurement in Physical Education and Exercise Science, 16: , 2012 Copyright Taylor & Francis Group, LLC ISSN: X print / online DOI: / X How Can Sport Biomechanics Contribute to the Advance of World Record and Best Athletic Performance? Li Li Department of Kinesiology, Louisiana State University, Baton Rouge, Louisiana Modern history has evidence that sport biomechanics provide valuable contribution in the pursuit of faster, higher, and stronger. In this article, the contribution of sport biomechanics to the Olympic Games has been divided into three different categories: improve the physical capacity of the athletes, develop innovative techniques in a given sport, and help athletes interact with the environment more effectively. Those avenues will continue to be the paths that biomechanics contributes to the world of sports. Readers concerned about injury prevention should seek sources elsewhere, since it is not the focus of the authors in this article. Key words: sports, biomechanics, Olympic INTRODUCTION Reported by AFP on April 26, 2012, Usain Bolt, the current 100m sprint world record holder could break his own record of 9.58 seconds and reach 9.49 seconds or lower during the London Olympics, predicted by his coach since 2004 (AFP, 2012). This is a topic how fast, high, and strong humans can be that has intrigued athletes, coaches, and sport enthusiasts throughout history. Is there a limit to human performance? What is the limit if there is one? Will the limit change with biological or technological developments? It may never be known if there is a limit, but world records have been renewed every year. It is clear that the limit has not been reached yet even if there is one. Among all of the tools that athletes and coaches have for the pursuit of faster, higher, and stronger, sport biomechanics is surely very effective in the past and will continue to be effective in the future. Sport biomechanics is a field of study that focuses on the results of muscle force application on human movement during sports. The ultimate goal of sport biomechanics study is to improve performance and prevent injury. From a sport biomechanics perspective, the record of human performance can be improved from three different aspects: enhancing the physical condition of the performer, improving the movement techniques involved in the performance, and optimizing the interaction between the athletes and the environment. People can be trained to reach better performance, said Usain Bolt and his coach. Among others in the history, Usain Bolt had proved to the world that training works (AFP, 2012). He is Correspondence should be sent to Li Li, Department of Kinesiology, 112 Long Field House, Louisiana State University, Baton Rouge, LA lli3@lsu.edu

2 BIOMECHANICS AND ATHLETIC PERFORMANCE 195 trying to provide new evidence to attest that training will continue to be effective even at his level of performance. In addition to training, gene doping could be the next frontier for producing super humans, warned by AAAS (Somer, 2007). All of these efforts are aimed at improving mechanical power output, efficiency, and proficiency of the athletes. There is a long history of technique innovations that help to push the limit of human performance. In addition to the improvements of an individual technique, the fundamentals of a particular event could also be redesigned. One obvious example is the evolution of high jumping skills. The world record created by the Eastern cut-off, the advanced style of the scissors technique, was 1.97m in The new technique, the Western roll, brought the world record to 2.01m during the 1912 Summer Olympics. The same technique has changed the performance little in 20 years, until the 1936 Summer Olympics, where the record was brought to 2.03m. The next revolution came with the straddle technique. The world record improved to 2.13m in 1956, 2.23m in 1960, and 2.28m in The Fosbury flop first time jumpers go over the bar in a belly-up position helped push the record to 2.33m in 1977 and 2.35m in The current world record is 2.45m, created in 1993 with the Fosbury flop. Figure 1 shows the progress of the word high jumping record since The influence of the straddle technique around 1960 and Fosbury flop in early 1990s is clearly shown in this graph with the records above the regression line (IAAF, 2009). Improving the environment, or how athletes interact with the environment, has been proven as a significant contributor to improve athletic performance as well. Improving the surface of a golf ball, swim suit material, running shoes, and tuned track are all examples in this category. Clap skates, speed skates with a hinge, made huge wave of braking world record during the 1998 Winter Olympic in Nagano, Japan. The significant improvement of men s 500m world record during the late 1990s, markers below the regression line can be observed in Figure 2. Biomechanics researchers can help improves athletic capacity of the athletes, contribute to the improvements of sport technique, and enable the athletes interact with the environment more effectively. These three factors, as illustrated in Figure 3, act collectivelyas the contribution of sport biomechanics on the worlds of sports (International Skating Union). FIGURE 1 Men s high jump world records from 1930, with linear regression line. World records accelerated with Western Roll in the late 1930s, Straddle in the late 1950s and early 1960s, and with Fosbury flop starting in the late 1970s. Data obtained from the International Association of Athletics Federations website (accessed May 18, 2012).

3 196 LI FIGURE 2 Men s 500m speed skate world records for the last 30 year with liner regression line. World records of 1998, 1999, 2000, and 2001 are far below the regression line. This demonstrates that world records have been renewed in a remarkable pace since the 1998 Nagano Winter Olympics, when clap skate had been introduced to the world speed skate stage. Data obtained from the International Skating Union website (accessed May 18, 2012). FIGURE 3 Sport biomechanics research can help the pursuit of faster, higher, and stronger by improving the strength of the athletes or improving athletic power putout through better motor coordination, better movement techniques, and better athlete interaction with the environment. BIOMECHANICS OF IMPROVING THE PHYSICAL CAPACITY OF THE ATHLETES There are many types of training that are aimed at improving the athletes physical capacities during a competition. Trainings can improve strength, endurance, flexibility, coordination, and neural acuity. Plyometric training and its effect on improving jumping height can be used as an

4 BIOMECHANICS AND ATHLETIC PERFORMANCE 197 example to illustrate how biomechanics can help in improving the athletes muscle power output. Plyometric exercise starts a movement to the opposite of the intended direction (Bobbert, 1990). Drop jump as one of the most popular plyometric exercises, is performed by stepping off a raised platform and immediately jumping vertically after landing on the ground (Bobbert, 1990). The platform can be various heights, but maximal jump height is always the goal of the subsequent jump. Researchers, coaches, and athletes have long believed that drop jump training can effectively improve vertical jumping height and other sports that require explosive power from the legs. It is assumed that this increase in vertical jumping height is the result of an enhanced muscle mechanical output during the concentric contraction phase, as illustrated by the greater power output observed in drop jumps as compared to vertical jumps starting from the ground level, such as the counter movement jump. Of course, greater peak power output can directly lead to greater take off velocity, where take off velocity determines the jump height (Horita, Komi, Nicol, & Kyröläinen, 2002). The basic muscle mechanics lead us to believe that stretch-shortening cycle (SSC), the main muscle action during drop jump, enhances human performance by taking advantage of muscle force length and force velocity relationships as well as impulse momentum relationships. According to Gordon and co-workers (Gordon, Huxley, & Julian, 1966), active components of muscle fibers produce maximum force at optimal muscle fiber length (Figure 4). Muscle could work at closer to the optimal length within a SSC comparing to the length without pre-stretch. The same would be true in the comparison from drop jump to static jump. With a similar principle, plyometric training can also enable the athletes to take advantage of the force velocity relationship (e.g., De Ruiter & De Haan, 2001). Muscle can produce more force during eccentric contraction comparing to isometric and concentric contractions, as illustrated in Figure 5. Plyometric training stretches the muscle first to take advantage of the eccentric contraction and then enables the athletes to produce more muscle force with the completion of the SSC. The athletes can also prolong the force application time during a SSC more than a static jump. According to the principle of impulse-momentum relationship, change of momentum (mass velocity) is a direct result of the product of force and the time of the force applied (force time of force application). Longer force application time contributes to greater take off velocity that leads to greater jump height. In addition to force length, force velocity, and impulse momentum relationships, other mechanisms that can also contribute to greater power output during a drop jump is stretch reflex (see Komi, 1984 for more detailed review on this topic), the storage and utilization of elastic energy (Bosco & Komi, 1979), and potentiation of the contractile machinery (Bobbert, Huijing, & van Ingen Schenau, 1987). First, the stretching of muscles during the landing of a drop jump may trigger a stretch reflex. Stretch reflex is a muscle contraction induced by stretching within the same muscle. It is a fast monosynaptic reflex that provides an automatic regulation of muscle length through increased muscle force production. It may increase muscular stiffness, leading to an improved ability to utilize storage of potential elastic energy. The effect of stretch reflex is increased with greater stretching velocity (Kallio, Linnamo, & Komi, 2004) where it can be achieved with optimal drop jump height (Ruan & Li, 2008). Second, elastic energy stored in the series elastic elements during stretching can be released during shortening (Bosco, Komi, & Ito, 1981). The storage and utilization of elastic energy is enhanced with high stretch speed, high eccentric force, and short time delay after the stretch (Bosco et al., 1981). Scientists have been long concerned about elastic energy storage during

5 198 LI FIGURE 4 Muscle force-length relationship (Gordon, Huxley, & Julian, 1966). There is an optimal length for muscle force production. With stretch-shortening cycle (SSC), as in plyometric training, muscle contraction could be using more of the top range on this curve comparing without pre-stretch. FIGURE 5 Muscle force-velocity relationship (De Ruiter and De Hann, 2001). Pre-stretched muscle could possibly take advantage of the greater muscle force production capacity with eccentric contraction. jumping (e.g., Asmussen & Bonde Petersen, 1974). By investigating the amount of elastic energy stored in the legs during squat-jump, counter movement jump, and drop jump, the scientists have concluded that there was elastic energy stored in the active muscles during the downward movement. However, the storage of elastic energy has been debated in the literature. Gerrit van Ingen Schenau (1984) stated that negligible elastic energy can be stored in muscle tissue, by his estimation. He then argued that the advantage of pre-stretch was accomplished by increasing mechanical efficiency. Third, the pre-stretch during SSC may induce potentiation of the contractile machinery (Cavagna & Citterio, 1974). Potentiation is a term used to describe the short-term increase of muscle force production capacity after an acute stretch. This phenomenon has been shown to increase with speed of stretch and to decrease with the amount of time delay after the stretch (Edman, Elzinga, & Noble, 1978). Ettema and co-workers (Ettema, Huijing, & de Haan, 1992) have studied the effect of pre-stretch on potentiation in detail. They conclude that an active

6 BIOMECHANICS AND ATHLETIC PERFORMANCE 199 pre-stretch causes visible enhancement in the contractile machinery during the subsequent muscle contraction. The effects of the enhancement are dependent on muscle length, stretching velocity, and the types of contraction following the pre-stretch. To be an effective training method, drop jumping should fully exploit these mechanisms to enhance athletic performance. The best way of using plyometric training is still a point of discussion in recent literature. For example, some recent researches had focused on the determination of optimal load for jump squat in order to maximize the effect of loaded plyometric training (e.g., Li, Olson, & Winchester, 2008). BIOMECHANICS OF ATHLETES AND ENVIRONMENT INTERACTION Biomechanics can help us to improve the interaction between the athletes and the environment. Swimming suits, running shoes, and aerodynamic javelins are just a few of such examples. To demonstrate the potential positive influence of these types of research, the success of clap skate in a wave of new world records during the late 1990s has been briefly discussed earlier in the text. Here is a more detailed account on how biomechanics research is part of this innovation. The main stage of the development of the clap skate was at the Human Movement Laboratory on the campus of Free University (Amsterdam). The laboratory was led by professors van Ingen Schenau and de Koning at the time. Human calf muscle (m. triceps surae) is a powerful muscle that helps humans push off the ground during walking and running. The lab in Free University first realized that the design of the traditional speed skates limits the use of this muscle. To push off the ice and propel the skater forward, the skate of the push-off foot has to be in full contact with the ice, therefore, no powerful plantar flexion (ankle joint extension) is allowed (more details in de Koning, Foster, Lampen, Hettinga, & Bobbert, 2005). In their 1996 research publication, van Ingen Schenau, De Groot, Scheurs, Meester, and De Koning, (1996) detailed the restrictions of the skate on the calf muscle. In their research about the coordination of the muscles that cross the knee and the ankle joint at the back of the leg, the investigators in the abovementioned lab point out that the ankle joint push off motion and the plantar flexion is afforded by both the calf muscle and the even stronger knee extensors quad muscles (van Soest, Schwab, Bobbert, & van Ingen Schenau, 1993). Before the push-off, the knee is in a flexed position, while the ankle joint is in a neutral or slightly dorsalflexed position. At the start of the push-off, knee extensors will start to straighten up the knee joint. Calf muscles will be stretched with the knee extension at the same time. A stretched calf muscle is a well-positioned muscle for ankle joint plantar flexion, but the traditional skate does not allow this well-positioned muscle to shorten, therefore it prevents the muscle from producing much-needed muscle power (van Ingen Schenau et al., 1996). Interestingly, this research was partially a result of the investigation of the injury of tibialis anterior muscle in front of the shin bone during speed skate. It was a common injury of the skaters. Through research, scientists had determined that this injury was related to the restricted use of the calf muscle. Tibialis anterior contraction is needed to stabilize the ankle joint and to balance the contraction of calf muscle, due to the inability of plantar flexion of the ankle joint. The plantar flexion is common during walking and running and so is more natural during human locomotion. Clap skates put a hinge under the ball of foot and release the attachment at the hind foot so the heel can be raised with ankle joint plantar flexion, which in turn seems like a suitable

7 200 LI solution to the problem of tibialis anterior injury. It releases the need of tibialis anterior over exertion, and it uses the power produced by the calf muscle at the same time. In the season, 11 skaters of the junior sections of the region of Zuid Holland of the Netherlands agreed to try out the newly designed clap skate. The athletes in the experiment had improved 6.2% on average, while others in the same league had only improved 2.5% in the same period of time (van Ingen Schenau et al., 1996). The highest rank of these skaters were 36th, 11th, and 8th in their own groups, junior A, B, and C ranking lists before the experiment. All three groups were led by people from the experiment using clap skates by the end of the season (van Ingen Schenau et al., 1996). The success of the Dutch athletes had encouraged athletes from all over the world to adapt to the clap skates right before the 1998 Winter Olympics in Japan. This worldwide success of clap skates is exemplified by the data shown in Figure 2 with the remarkable pace of new world record in the 500m speed skate race. In the words of a CCN reporter, The reason the records have been falling like a house of cards is because of the clap skate (International Skating Union). BIOMECHANICS AND THE TECHNICAL INNOVATION OF MOVEMENT TECHNIQUES IN SPORTS There are many examples of biomechanical analysis of a movement technique that can be used to help athletes to improve their performance. One example is to realize the importance of the lifting force acting on the hand during swimming. Through a series of research in the late 1960s and early 1970s, swimmers now are using a hand posture that emphasizes on the propulsive lift force as well as the propulsive drag force. This innovative development was correlated tightly with the rapid renew of world records during the early 1970s. Details about this work can be found in the 1992 review by Toussaint and Beek (1992). The biomechanics lab in Louisiana State University in the United States conducted a multiyear project with U.S. women s shot putters. Here is a recount of what they did. This research can be used as an example for how biomechanics can help improve performance through technological intervention. Details of this project can be found elsewhere (Young, 2009; Young & Li, 2005). There were previous optimization attempts on other events, for example, running (Yanai & Hay, 2004), gymnastics backwards long swings on rings (Yeadon & Berwin, 2003), and triple jump (Yu & Hay, 1996). However, it is unknown if optimization would work for shot put. Conceptually, it would be an ideal movement for optimization, since it is a discrete task that takes place in a closed environment. A pilot study was conducted by Li and Young to determine whether optimization modeling techniques could be used for shot put. Results of the pilot study provided strong support for the development of an optimization model for shot put. The critical parameters for success among elite women shot putters had been examined first. Parameters that were important for elite-level performance were selected. The results suggested that, among high level shot putters, greater rear knee flexion at rear foot touchdown and at release increased release velocity. A more neutral shoulder-hip separation at release and a greater horizontal release distance were the best predictors of a good performance at elite level. Although the observations were not conclusive, due to a very limited data set, they provided sufficient support for developing an optimization model for elite-level women s shot put.

8 BIOMECHANICS AND ATHLETIC PERFORMANCE 201 The optimization study used two hierarchical linear-modeling analyses to determine that all critical parameters were significant contributors to elite-level performance in the women s shot put. The first analysis examined each parameter individually and indicated that seven of the selected variables had a significant impact on the measured distance of the throw. They all contributed to elite-level success among women shot putters at the US national competition level. The second hierarchical linear-modeling analysis examined the unique effects of each parameter in a model containing all critical variables and indicated that release angle, peak center of mass vertical displacement of the athlete plus shot system during the flight phase, shoulder-hip orientation at rear foot touchdown, and rear knee angle at release made unique and significant contributions to the performance. These observations largely validated the findings of the previous study and established the first optimization model for elite female shot putting. Results of the optimization model have then been tested by the effectiveness of a technical intervention. The results show that athletes that were trained based on the optimization model performed much better than the comparison group for their yearly progresses, although the inter-year performance differences were clinically but not statistically significant. The intervention group s inter-year performance improvements were more than twice that of the non-intervention group. The results indicate that the technical intervention produced beneficial changes in performance that were closely linked with the critical parameters identified within the optimization modeling process. More details can be found elsewhere (Young, 2009). In conclusion, from the changes of high jumping style to the hand position change during swimming to improving rear knee joint angles among shot putters, sport biomechanics has a lot to contribute to progress of sport performance. SUMMARY Sport biomechanics research can help the Olympic sports achieve the goals of faster, higher and stronger by improving performance and injury prevention. Only the improved performance part of the equation is focused in this article, but please note that biomechanics can equally contribute to the efforts of injury reduction. Sport biomechanics can help athletes improve their body s capacity (which leads to greater mechanical energy output), interact with the environment more efficiently (which enables their efforts to be more effective) and develop innovative movement techniques that can revolutionize a given event. Past history shows that biomechanical research has played an integral part in the pursuit of superior sport performances. Future research will provide more evidence to support that sport biomechanics is a valuable tool in improving Olympic competitions. REFERENCES AFP. (2012). Bolt can take 100m world record below 9.5, says coach. Google News. Retrieved from 97faeb0d290d24ff91c7fcf28bb4e37e.431 Asmussen, E., & Bonde Petersen. F. (1974) Storage of elastic energy in skeletal muscles in man. Acta Physiologica Scandinavica, 91, Bobbert, M. F., (1990). Drop jumping as a training method for jumping ability. Sports Medicine, 9, 7 22.

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