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Bradley S. Beardt, Myranda R. McCollum, Taylour J. Hinshaw, Jacob S. Layer, Margaret A. Wilson, Qin Zhu and Boyi Dai

be utilized to understand whether controlled tasks could represent movement patterns and their associated injury risk during sports competition. Therefore, the purpose of this study was to quantify the differences and correlations in jump-landing kinematics among a drop-jump, a controlled volleyball-takeoff

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Christopher D. Ramos, Melvin Ramey, Rand R. Wilcox and Jill L. McNitt-Gray

momentum by generating linear and angular impulse during interaction with the ground. During the takeoff phase, vertical and horizontal impulse generation requires control of the total body center of mass (CM) trajectory in relation to the reaction forces (RFs) generated during contact with the ground. 1

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Mikko Virmavirta and Paavo V. Komi

This study measured the takeoff forces exerted by jumpers during the 70-m ski jumping competition of the 1988 Winter Olympics in Calgary. Instrumentation consisted of four force plates installed under the snow of the takeoff platform. The results indicated that the greatest force was already exerted 149±9 ms before the release. The second force peak appeared closer to the edge of the takeoff platform. The correlations between the variables measured in this study were generally weak but some were considered important. The official approach velocity of the first round and relative maximum force as well as the mean relative force during the whole takeoff sequence of the second round correlated to length of jump. The mean relative forces at the end of takeoff and for the whole takeoff sequence were significantly higher among the best jumpers. It is concluded that although the force analyses among the jumpers do not reveal conclusive interrelationships, the fast development of the takeoff forces may be an important prerequisite for successful ski jump performance.

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Inseong Hwang, Gukung Seo and Zhi Cheng Liu

This study examined the biomechanical profiles of the takeoff phase of double backward somersaults in three flight positions: seven layout double backward somersaults (L), seven twisting double backward somersaults (TW), and seven tucked double backward somersaults (TDB). Selected kinematic variables and angular momenta were calculated in order to compare the differences resulting from different aerial maneuvers. The amount of total body angular momentum about the transverse axis through the gymnasts' center of mass progressively increased from TDB to TW to L. The gymnasts performing the skill in the layout position tried to minimize the angle of block in a direction opposite the intended motion by maximizing the angle of touchdown and takeoff. In so doing, the horizontal velocity center-of-mass curve of the L showed a slowly decreasing curve compared with those of the other two somersaults while the vertical velocity curve of the L increased more slowly than the other curves during the takeoff phase. In all cases the legs played the dominant role in contributing to total angular momentum during takeoff.

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Mikko Virmavirta and Paavo V. Komi

The Paromed Datalogger® with two insole pressure transducers (16 sensors each, 200 Hz) was applied to study the feasibility of the system for measurement of plantar pressure distribution in ski jumping. The specific aim was to test the sensitivity of the Paromed system to the changes in plantar pressure distribution in ski jumping. Three international level ski jumpers served as subjects during the testing of the system. The Datalogger was fixed to the jumpers’ lower back under the jumping suit. A separate pulse was transmitted to the Datalogger and tape recorder in order to synchronize the logger information with photocell signals indicating the location of the jumper on the inrun. Test procedure showed that this system could be used in ski jumping with only minor disturbance to the jumper. The measured relative pressure increase during the inrun curve matched well the calculated relative centrifugal force (mv2 · r‒1), which thus serves a rough estimation of the system validity. Strong increase in pressure under the big toes compared to the heels (225% and 91%, respectively) with large interindividual differences characterized the take-off. These differences may reflect an unstable anteroposterior balance of a jumper while he tries to create a proper forward rotation for a good flight position.

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Nicholas P. Linthorne

A mathematical model is presented of the takeoff phase in the pole vault for an athlete vaulting with a rigid pole. An expression is derived that gives the maximum height that the vaulter may grip on the pole in terms of the takeoff velocity, the takeoff angle, the athlete's vertical reach, and the depth of the takeoff box. Including the dependence of the vaulter's takeoff velocity on the takeoff angle reveals that there is an optimum takeoff angle that maximizes the vaulter's grip height. It is also shown that taller and faster vaulters are able to grip higher on the pole. The results of the investigation compare favorably with data for vaulters using bamboo and steel poles.

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Mikko Virmavirta, Juha Kivekäs and Paavo Komi

The effect of skis on the force–time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.

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Doris I. Miller and Carolyn F. Munro

A temporal and joint position analysis was conducted on Greg Louganis' forward and reverse 3-m springboard takeoffs performed during National Sports Festival V in Colorado Springs. The most notable differences between Louganis' technique and those of eight women finalists in the 1982 Canadian Winter Nationals (Miller & Munro, 1984) were in his greater ranges of joint motion particularly at the knees, hips, and shoulders. He also employed a straighter arm-swing. The fact that Louganis' takeoff duration averaged 0.45 ± 0.01 s, compared with a mean of 0.38 s for the women, allowed him more time to complete joint flexion and extension. This raised questions of adapting technique to progressive changes in skill and strength and monitoring improvement in performance objectively on a longitudinal basis.

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Wayne J. Albert and Doris I. Miller

Takeoff kinematics of axel jumps were determined from a spatial analysis of singles and doubles performed by 16 figure skaters. The takeoff was divided into glide, transition, and pivot phases. During the glide, horizontal speed remained constant, vertical velocity was slightly negative, and over half the angular momentum for flight was generated. In the transition, skaters gained considerable vertical velocity from tangential motion by rotating about the long axis of the blade, Initially this reduced the angle of the support leg with respect to the vertical while the blade ran in the direction of progression. Most skaters continued to gain vertical velocity by angling the blade to the direction of progression (skidding) and rotating up and forward, still about the blade's long axis. There was little angular momentum gain, and forward speed decreased significantly. In the pivot, skaters rocked forward onto the toe picks losing horizontal speed, vertical velocity, and angular momentum.

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Doris I. Miller and Carolyn F. Munro

A linear and angular momentum analysis was conducted on Greg Louganis' forward and reverse 3-m springboard takeoffs performed during National Sports Festival V in Colorado Springs, and differences among dives were examined. At initial contact with the board, his horizontal velocity approximated 0.5 m/s across all dives analyzed. In the forward 3.5 somersaults pike, the horizontal velocity subsequently increased in magnitude until the latter half of recoil. By contrast, in the forward and reverse dives and reverse 2.5 somersaults, horizontal velocity displayed an initial reduction followed by an increase to the final value of 0.8 to 1.2 m/s. His vertical velocities at touchdown (−4.3 to −4.5 m/s) increased to 5.0 to 6.0 m/s during the takeoff, with the final upward velocity being related to the type of dive performed. At initial contact, Louganis’ total body angular momentum with respect to his center of gravity was negligible. By the end of the takeoff, it had increased to 18 kg-m-m/s for the forward dive straight and was three and four times that magnitude for his reverse 2.5 and forward 3.5 somersaults pike, respectively. Between 80 and 90% of the total angular momentum at the end of the takeoff was due to the segment remote contributions. The importance of the upper extremities in developing somersaulting angular momentum was shown by the fact that they were responsible for between 30 and 43% of the final angular momentum in all but the forward dive straight.