Kinetics of Discus Throwing

 

As a coach initiated project, we conducted a study on the kinetics of discus throwing techniques in collaboration with former men's discus throw world record holder and US men's discus throw coach, Dr. Jay Silvester, and biomechanist at US Olympic Committee, Dr. Jeffery Broker. The purpose of this study were to investigate (1) the relationship between official distance and selected ground reaction force measures during discus throwing; and (2) the relationship between selected ground reaction force measures and selected lower extremity joint kinetics. An understanding of these relationships may provide critical information for technical and physical training of elite discus throwers. Eight elite male discus throwers in a 1998 discus training camp at the US Olympic Training Center in San Diego were recruited as the subjects for this study. Three high speed video cameras were used to collect three-dimensional coordinate data while three force plates were used to collect ground reaction force data of discus throw for each subject during discus throw. Ground reaction forces and impulses and lower extremity joint resultant forces and moments at selected critical instants and phases of the discus throw were reduced for each subject in each trial.

The results of this study showed significant correlations of official distance and selected ground reaction force measures and joint resultant measures. These results have the following important implications to coaches and athletes: (1) a discus thrower should drive his or her body-plus-discus system as vigorously as possible towards the throwing direction during the first single support phase, (2) a discus thrower should also generate a certain amount of vertical thrust during the first single support phase to have a certain height of flight, (3) the concept that discus throwers should jump as low as possible for the flight is not supported by these results, (4) a hard right foot landing after the flight may assist discus throwers to generate ground reaction impulses on the right foot during the second single support phase and delivery phase for long official distance, (5) a discus thrower should drive his or her right leg forward and rightward during the second single support phase and delivery phase for long official distance, (6) a discus throwers should also drive his or her left leg upwards and backwards as vigorously as possible during delivery phase, and (7) hip and knee extension strengths are critical for right and left legs' drives during the second single support and delivery phases. These results indicate a possibility to use force plates as quick feedback tool for technical training of the discus throw. A new force plate formation for measurement of ground reaction forces in discus throw and corresponding computer programs were designed at the Center for Human Movement Science and proposed to the US Olympic Committee.

 

 

Optimum Release Angle

 

Currently we are conducting a study on the optimum release angle of discus throw. The angle of release is an important release parameter that affects the official distance. Although recent studies reported the release conditions of elite discus throwers similar to those reported in early literature, there was no evidence that those reported actual release conditions were indeed optimal. It has also been noticed that the studies on the optimal release conditions for discus throwing were based on many assumptions. The validity of these assumptions may have significant effects on the validity of the results in previous studies. One of the assumptions in previous studies on the optimal release conditions in discus throwing and other projectile motions that have not been noticed is the assumption that the speed of the discus at release is a constant that is not affected by the angle of release. The validity of this assumption threatens the validity of the optimal angle reported in literature, and is an obstacle for our further understanding of discus throwing techniques as well as other human projectile motions. The speed of the discus at release should be correlated to the angle of release if the speed of the discus at release is not a constant as the angle of release changes in maximum effort throws. The relationships of the speed of the discus at the release with the angle of release and the relationship of the aerodynamic distance with selected release conditions would provide basis for determining optimal angle of release.

The purposes of this study were (1) examine the relationship of the speed of release with the angle of release and horizontal and vertical speed of the release for selected individual men and women's discus throwers, (2) examine the relationship of the aerodynamic distance with speed of the discus at the release and the angle of release, and (3) determine the optimal angle of release for these individual discus throwers.

Three elite male and four elite female discus throwers who had at least eight trials in our discus throw database were used as the subjects for this study. Two high speed video camcorders were used to record subjects' performances at a frame rate of 60 frames/second in each competition. The flight distances, aerodynamic distances, discus horizontal, vertical, and resultant speeds at the release, height of release, and angle of release were reduced.

The results of this study showed that the magnitude of the resultant speed of the discus at the release is a function of the angle of release. The effects of angle of release on the magnitude of the resultant speed of the discus are different from athletes to athletes. The optimum angle of release, therefore, is an individualized release parameter. Although that the optimal angle of release for some athletes is between 35 and 40 as literature show, the optimal angle of release for some other athletes could be less than 35 or greater than 40. The optimal angle of release for women's discus throwers tends to be greater than that for men's discus throwers. In addition, an angle of release no more than 2 away from the optimal angle of release would affect the actual distance no more than 0.2 m, but an angle of release more than 5 away from the optimal angle of release would decrease the actual distance by up to 1.26 m. Further more, an angle of release smaller than the optimal angle of release decreases the actual distance more than an angle of release greater than the optimal angle of release does. These findings indicate that the angle of release is indeed an important release condition with a narrow margin for error in discus throw, and that the optimal angles of release for discus throw recommended in literature may not necessarily be appropriate references for every athlete.