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Prediction of optimal fulcrum setting for backward takeoffs
306
Abstracts
PREDICTION OF OPTIMAL FULCRUM SETTING FOR BACKWARD TAKEOFFS W.L. Boda and J. Hamill Biomechanics Laboratory, Department of Exercise Science University of Massachusetts, Amherst, MA 01003 In springboard diving, the effect of the fulcrum setting on height generated during a backward takeoff is critical because proper timing between the diver and springboard is essential for generating heightThe purpose of this study was to formulate a prediction equation in order to predict the fulcrum setting at which a diver generates the greatest amount of height. Twenty collegiate divers participated in the study. High-speed video data were collected at 60 Hz with a shutter speed of l/250 sec. The video data were digitized using a Motion Analysis VP110 processor interfaced to a Sun minicomputer. Divers, simulating a backward press, oscillated on the ground in a laboratory session and on the board in a pool session. They were video-taped while oscillating at fulcrum settings of 1,3,5.7,9 and at their preferred fulcrum setting (PFS) on the spring board and at their preferred frequency in the laboratory (PFL). Maximum jump height was used as the independent variable. The prediction equation was obtained by performing a bootstrap analysis in conjunction with a stepwise regression analysis. The bootstrap technique used repeated random samples of 15 subjects from the total subject pool with the remainiig 5 subjects from each random sample functioning as a holdout group. The resulting regression equations were used to generate an overall equation. The final equation predicting the optimal fulcrum setting 01) was: y = 10.46 + 1.24 B1 - 4.50 B2 - 0.03 B3 where Bi = PFS, B2 = PFL, and B3 = body mass. The results of this analysis indicated that it was possible to predict the fulcrum setting at which the diver generated the most height. The results indicated that preferred fulcrum setting, diver mass and oscillation rate on the ground were good predictors of fulcrum setting explaining 82% of the variance in the equation.
THE INFLUENCE OF RUN-UP DISTANCE ONTO GROUND REACTION FORCE AND PRESSURE DISTRIBUTION PARAMETERS E. M. Hennig and G. A. Valiant Sportmedizinisches Ins&t, Universit&t Essen. Essen, Germany Niie Sport Research Laboratory, Portland, Oregon, USA This study was performed to estimate the necessary space requirements for reliable force platform and pressure distribution measurements in overground running. Fourteen male subjects performed 8 repetitive running trials (3.83 m/s) across a 40 cm by 60 cm “Kistler” force platform in each of three run-up distance conditions. The minimum dlsta&e was defined by a 3-Step, the medium distance by a 5-Step run-up. A Free-Run was chosenas third condition. The order of the conditions was randomized.The experimentstook place in a large laboratory facility with more than 15 m of space to both sides of the force platform arrangement. The vertical and horizontal ground reaction forces and in-shoe pressure distributions under 8 anatomical locations of the foot were measured. The transducers were placed under the lateral and medial heel, lateral and medial midfoot, under the lst, 3rd and 5th metatarsal heads and the hallux. Data collection was done at a rate of 1 kHz per channel at a resolution of 12 bit. A comparison of the 5-Step and the Free-Run revealed no significant differences for any of the force and pressure parameters. However, the 3-Step condition showed highly significantly reduced fiit vertical peak force values, increased peak horizontal forces, reduced peak pressures in the heel region, and increased pressures under the 3rd metatarsal head. The intraindividual coefficient of variability for the first vertical force peak value was significantly less in the 5-Step as compared to the Free-Run and the 3-Step conditions. Since no significant differences could be found in any of the parameters between the 5-Step and Free-Run conditions, a reduced coefficient of variability in the 5-Step run-up offers an advantage. Force platform measurements for the shorter running distance demonstrated less variability while showing almost identical force and pressure patterns, as they are found in a Free-Run situation
TECHNIQUES USED BY ELITE GYMNASTS IN PERFORMINGTHE COMPULSORY PARALLEL BAR MOUNT FOR THE 1992 OLYMPIC GAMES Y. Takei, H. Nohara*, and M. Kamimura*, Dept. of Physical Education, Northern Illinois University, DeKalb, IL 66115, USA and *Dept. of Physical Education, Kyoto University of Education, Kyoto, Japan. The purpose of the study was to identifythe mechanical factors that are crucial to successful performance of the basket to handstand mount on the parallel bars. A 16mm Locam II camera, filming at 100 Hz, was used to record the mounts performed by 25 US and 26 Japanese gymnasts competing in their respective 1990 national championships. The average of 4 middle scores awarded by 6 judges with international certificationwas used to arrive at the final score for each mount. A deterministic model was developed to identify the mechanical factors that detennlne the linear and angular motions and form of the mount. Significant correlations @ ~661) indicated that (a) large vertical displacement (0,) of CG from body compression to bar release, (b) large backward horizontal velocity (VJ at bar release, (c) large backward horizontal displacement (DJ of CG in flight, (d) large forward angular displacement of body rotation, angular velocity, and angular momentum In flight, (e) great height of CO at bar regrasp, (9 large backward 0, and V, of CG from the regrasp to handstand, (g) small 0, of CG and short time from the regrasp to handstand, and (h) large normalized moment of Inertia at handstand are important for successful performance. The conclusions were that focus should therefore be made to achieve a (a) large upward D, of CG from body compression to bar release by exerting an arm pull of long duration till the shoulders are above the bars, (b) backward 0, of CO and simultaneous forward rotation of the body toward the handstand position while in the air, (c) great height of CG and full body extension at bar regrasp, (d) steady backward horizontal motion of CG and simultaneous forward body rotation during the regrasp to handstand, and (e) fully extended handstand position for successful performance of the basket to handstand mount.
Abstracts
PREDICTION OF OPTIMAL FULCRUM SETTING FOR BACKWARD TAKEOFFS W.L. Boda and J. Hamill Biomechanics Laboratory, Department of Exercise Science University of Massachusetts, Amherst, MA 01003 In springboard diving, the effect of the fulcrum setting on height generated during a backward takeoff is critical because proper timing between the diver and springboard is essential for generating heightThe purpose of this study was to formulate a prediction equation in order to predict the fulcrum setting at which a diver generates the greatest amount of height. Twenty collegiate divers participated in the study. High-speed video data were collected at 60 Hz with a shutter speed of l/250 sec. The video data were digitized using a Motion Analysis VP110 processor interfaced to a Sun minicomputer. Divers, simulating a backward press, oscillated on the ground in a laboratory session and on the board in a pool session. They were video-taped while oscillating at fulcrum settings of 1,3,5.7,9 and at their preferred fulcrum setting (PFS) on the spring board and at their preferred frequency in the laboratory (PFL). Maximum jump height was used as the independent variable. The prediction equation was obtained by performing a bootstrap analysis in conjunction with a stepwise regression analysis. The bootstrap technique used repeated random samples of 15 subjects from the total subject pool with the remainiig 5 subjects from each random sample functioning as a holdout group. The resulting regression equations were used to generate an overall equation. The final equation predicting the optimal fulcrum setting 01) was: y = 10.46 + 1.24 B1 - 4.50 B2 - 0.03 B3 where Bi = PFS, B2 = PFL, and B3 = body mass. The results of this analysis indicated that it was possible to predict the fulcrum setting at which the diver generated the most height. The results indicated that preferred fulcrum setting, diver mass and oscillation rate on the ground were good predictors of fulcrum setting explaining 82% of the variance in the equation.
THE INFLUENCE OF RUN-UP DISTANCE ONTO GROUND REACTION FORCE AND PRESSURE DISTRIBUTION PARAMETERS E. M. Hennig and G. A. Valiant Sportmedizinisches Ins&t, Universit&t Essen. Essen, Germany Niie Sport Research Laboratory, Portland, Oregon, USA This study was performed to estimate the necessary space requirements for reliable force platform and pressure distribution measurements in overground running. Fourteen male subjects performed 8 repetitive running trials (3.83 m/s) across a 40 cm by 60 cm “Kistler” force platform in each of three run-up distance conditions. The minimum dlsta&e was defined by a 3-Step, the medium distance by a 5-Step run-up. A Free-Run was chosenas third condition. The order of the conditions was randomized.The experimentstook place in a large laboratory facility with more than 15 m of space to both sides of the force platform arrangement. The vertical and horizontal ground reaction forces and in-shoe pressure distributions under 8 anatomical locations of the foot were measured. The transducers were placed under the lateral and medial heel, lateral and medial midfoot, under the lst, 3rd and 5th metatarsal heads and the hallux. Data collection was done at a rate of 1 kHz per channel at a resolution of 12 bit. A comparison of the 5-Step and the Free-Run revealed no significant differences for any of the force and pressure parameters. However, the 3-Step condition showed highly significantly reduced fiit vertical peak force values, increased peak horizontal forces, reduced peak pressures in the heel region, and increased pressures under the 3rd metatarsal head. The intraindividual coefficient of variability for the first vertical force peak value was significantly less in the 5-Step as compared to the Free-Run and the 3-Step conditions. Since no significant differences could be found in any of the parameters between the 5-Step and Free-Run conditions, a reduced coefficient of variability in the 5-Step run-up offers an advantage. Force platform measurements for the shorter running distance demonstrated less variability while showing almost identical force and pressure patterns, as they are found in a Free-Run situation
TECHNIQUES USED BY ELITE GYMNASTS IN PERFORMINGTHE COMPULSORY PARALLEL BAR MOUNT FOR THE 1992 OLYMPIC GAMES Y. Takei, H. Nohara*, and M. Kamimura*, Dept. of Physical Education, Northern Illinois University, DeKalb, IL 66115, USA and *Dept. of Physical Education, Kyoto University of Education, Kyoto, Japan. The purpose of the study was to identifythe mechanical factors that are crucial to successful performance of the basket to handstand mount on the parallel bars. A 16mm Locam II camera, filming at 100 Hz, was used to record the mounts performed by 25 US and 26 Japanese gymnasts competing in their respective 1990 national championships. The average of 4 middle scores awarded by 6 judges with international certificationwas used to arrive at the final score for each mount. A deterministic model was developed to identify the mechanical factors that detennlne the linear and angular motions and form of the mount. Significant correlations @ ~661) indicated that (a) large vertical displacement (0,) of CG from body compression to bar release, (b) large backward horizontal velocity (VJ at bar release, (c) large backward horizontal displacement (DJ of CG in flight, (d) large forward angular displacement of body rotation, angular velocity, and angular momentum In flight, (e) great height of CO at bar regrasp, (9 large backward 0, and V, of CG from the regrasp to handstand, (g) small 0, of CG and short time from the regrasp to handstand, and (h) large normalized moment of Inertia at handstand are important for successful performance. The conclusions were that focus should therefore be made to achieve a (a) large upward D, of CG from body compression to bar release by exerting an arm pull of long duration till the shoulders are above the bars, (b) backward 0, of CO and simultaneous forward rotation of the body toward the handstand position while in the air, (c) great height of CG and full body extension at bar regrasp, (d) steady backward horizontal motion of CG and simultaneous forward body rotation during the regrasp to handstand, and (e) fully extended handstand position for successful performance of the basket to handstand mount.