Mechanics of Vertical Jumping(taken from the book jumping into plyometrics)
Vertical jumping is a component of most sport activities. It is often taken for granted that an athlete instinctually knows how to jump Vertically. In actuality, jumping vertically is a skill that can and should be tought to athletes. If we examine the even a little more closely we find that the jump is preceded by a countermovement, in which the centre of gravity(C of G) drops rapidly. This is seen as a flexing of the hips, knees, and ankles of an athlete. The trunk tilts slightly forward and the arms are pulled to a position behind the midline of the body. Prior to the vertical movement of the body, there is a rapid extension of the hips, knees, and ankles, which is largely the result of force developed by the arms and legs. The arms should be brought forward rapidly and allowed to travel to a position above and in front of the shoulders. The quick bend of the knees which lowers the C of G is accompanied by moving the arms into a position where the shoulders are extended and the arms are behind the athlete. This position of the arms allows the athlete to develope force which is directed into the ground as the arms come forward. Interestingly enough, once the arms pass the midline of the body they can no longer develope force that will help achieve overall height. Past this point they are only able to decelerate, and this allows the body to begin liftoff. Therefore, it is important to get the arms as far back and as straight as possible for maximum force development. The more the arms bend at the elbow the faster they will come through, but the less they will contribute to overall force development. A practical view of this is to compare the arm swing of elite triple jumpers versus that of elite high jumpers. Where maximum force is important for the triple jumper, high jumpers useing the flop technique must rely more on arm speed to effectively carry out their technique.
Research by Everett Harman, PhD, et al. (1991) at the U.S. Army Research Institute of Environmental Medicine has shown that the countermovement is crucial to development of force and can contribute up to six percent of the total jump height. B]The arms can increase the overall jump height by as much as 21 percent.[/B] It was concluded that the arms developed their positive effect by exerting downward force on the body as they swung through in the early phase of the jump and kept the body in a position such that the quadriceps and gluteus muscles could exert force over a longer period of time. It was also concluded that since the countermovement did not contribute that significantly to jump height, many sport situations may not require a countermovement in order for the athlete to be effective. If speed of movement and reaction time is more crucial, such as in a volleyball block, the athlete may be just as effective by simply starting the jump with the knees bent. In other words, if an athlete does not need to attain maximum height a no-countermovement will clearly be more effective.
Due to the arms' large contribution to overall jump height it appears that strengthening these areas through resistance training exercises would be an important component of all jump training programs. Some of these exercises seen as important in the development of the arms for jumping include the following
1 - Reverse Pull-downs
2 - Tricept dips
3 - Shoulder swings
4 - Straight arm latteral pull downs
5 - seated rows
6 - Backwards Medicin ball throws
7 - Underhand medicin ball throws
Hope you get some benefit out of this. oh and Karma is welcome too
