The Transfer Of Momentum In Fiberglass Pole Vaulting

By David R. Bussabarger

    This is the latest from pole vault technician Bussabarger. He tell us that his thoughts on the fundamental mechanical principles underlying fiberglass technique do not gibe with the current vogues, but his ideas do not "come out of the void." He reminds us of a quote from an 1972 article by Ken Bosen entitled Comparison of Rigid and Flexible Pole Vaulting Technique: "He [the vaulter] must never forget that he is trying to change the linear momentum of the run into angular momentum for height. In order to effect change of direction in the body, a certain amount of force must be used. For this purpose present-day (fiberglass) vaulters use a forward-upward spring at takeoff" That seemingly uncontroversial statement provides a foundation for Bussabarger's thinking in this article.

    Although it is rarely recognized, the most fundamental principle of proficient vaulting technique is that the vaulter must successfully transfer developed forward/linear body momentum into vertical body momentum by establishing a correct flight path through the vault. Note that momentum is, in effect, a form of kinetic energy.
    This principle underlies all proficient vaulting technique, re­gardless of stylistic variations or the type of pole used.
    The flight path of the vaulter is determined by plotting a line through the vaulter's hips from the beginning of the takeoff to the completion of the vault. Note that the center of gravity is not used as a reference point because its location varies within and without the body, depending on specific body positioning.
    Given correct execution, the vaulter can generate substantial vertical propulsion in the final stages of the vault based solely on this process. Keep in mind that the best rigid vaulters of the 1940's and 50's utilized this principle to vault in excess of three feet over their top hand without the aid of any pole spring.
    In theory the bend of fiberglass poles should permit the develop­ment of a much more efficient flight path through the vault (vis-á-vis rigid vaulters). This is because the bend of the pole allows the vaulter to gain height much more gradually and progressively from the takeoff through the rock­back. This, in turn, conserves the vaulter's body momentum during these phases. As a result, the flow of momentum through the vault should be increased, leading to greater vertical propulsion at the top of the vault (a superior mo­mentum transfer process).
    The best fiberglass technicians have achieved push-offs slightly in excess of four feet. Given that fiberglass vaulters have the added benefit of the spring of the pole to boost them vertically, it seems to the writer that current top push-off distances should be substantially higher. The fact that they are not indicates that fiberglass vaulters have yet to fully master the mo­mentum transfer process.
    Since the introduction of highly flexible fiberglass poles in the early 1960's, coaches and vaulters have almost always focused first and foremost on exploiting the catapult aspect of the vault. This writer, however, believes that fiberglass technique should be based on and designed around a proficient M.T.P. (Momentum Transfer Process). This is because in addition to its previously stated advantages, a superior M.T.P. should also naturally produce a superior catapult action. Most importantly a proficient M.T.P. produces negative "G" forces in the vaulter's body in the upper stages of the vault. The resulting decrease in the vaulter's effective weight then enhances the recoil power of the pole (all proficient fiberglass vaulters take advantage of this principle in varying degrees of success, whether they are aware of it or not.).
    Technical analysis is this article is based on a spacially accurate tracing of a photo sequence of Thierry Vigneron (the first man over 19 feet-1981), PR 19'4¾" WR, 1984). The source of the sequence is Peter Sutcliffe's British AAA booklet Pole Vault.
    The writer chose this particular photo sequence for two reasons:
        A. The high quality of the original sequence.
        B. The fact that on this particular vault Vigneron's flight path is extremely good. Note the gradual and progressive elevation of the hips from the takeoff through the rock-back.
    Also note the excellent align­ment of the hips from figure to figure, promoting the efficient flow of momentum through the vault.

IMPORTANT TECHNICAL POINTS

    1. Any delays or pauses in the movement of the body during the vault will cause the vaulter to lose momentum. Therefore the overall vaulting action should be as continuous as possible. Once the vaulter starts moving, he/she should not stop moving until the vault is completed. Keep in mind that the vaulter can make slight changes in the pace of movement at any given point while still maintaining continuous movement.
    2. The successful execution of the takeoff, which this writer considers the single most critical phase of the vault, depends greatly on the effective execution of the run and plant (which can be considered preliminaries of the takeoff). It is particularly important for the vaulter to remain erect and sustain an aggressive striding action in the final stages of the run and through the plant. This action enhances the force of the takeoff.
    3. The correct execution of the takeoff powerfully launches the vaulter off the ground and begins the change in direction of movement which primarily determines the vaulter's flight through the vault. Failure to execute the takeoff effectively will have a pronounced negative impact on all subsequent phases of the vault (hence its critical importance).
    4. Despite the crucial importance of the takeoff, flaws in execution can occur at any point in the vault after the takeoff (independent of an effective takeoff action). These flaws can, by themselves, have a significant negative impact of the outcome of the vault.
    5. Almost all coaches and vaulters today advocate taking off with the front of the foot of the take­off leg, vertically aligned with the top hand at the completion of the plant (Fig. 4). However, from a practical point of view it is possible to achieve out­standing results taking off as much as 12" farther forward (or "under"). For example, Tim Lobinger (PR 19'8¼"), Danny Ecker (PR 19'8¼") and Bjorn Otto (PR 19'4¼") all typically take off about 12" "under". An important point here is that the farther "under" the takeoff point is, the earlier the plant must be completed.
    6. The leg action in a proficient fiberglass takeoff can be described as a combined run-off/spring-off action (Figs. 1 to 7). That is, the vaulter should run continuously over the takeoff foot while allowing only minimal flexion in the takeoff leg. The free or lead leg should hesitate only for a tiny fraction of a second before it begins its forward to upward driving action. This slight hesitation promotes a more forceful lead leg/knee drive. Given correct execution, the run-off/spring­off action minimizes the loss of forward momentum during the takeoff.
    7. Vigneron, like the great ma­jority of fiberglass vaulters, depends on the driving action of the lead leg/knee to produce the desired gentle up-curved takeoff flight path (Figs. 2 to 7). This flight path conserves "inward" momentum and allows the vaulter's takeoff movement to flow efficiently into the following swing.
    For optimum results the driving action of the lead leg/ knee must be forward to up­ward in direction. If the lead leg/knee drives directly up­ward (a common fault among novices) the vaulter's takeoff flight will be distorted, causing a loss of "inward" momen­tum.
    Vigneron displays very good forward to upward lead leg/knee drive (Figs. 4 to 7). However he does not sustain upward knee pressure (as he should) at the completion of the takeoff (Fig. 7).
    Note that vaulters using a "hang" style takeoff action such as Steve Hooker, Yevgeniy Lukyanenko and Earl Bell pri­marily control takeoff flight by manipulating the action and positioning of the upper body (versus utilizing the drive of the lead leg/knee).
    8. The torso should be erect and press forward as the vaulter leaves the ground (Figs. 4 to 6). Note that Vigneron's torso is already well past his take­off point in Fig. 6 (indicating good torso pressure). This action significantly increases the launching power of the takeoff. A critical point here is that the driving force of the lead leg/ knee must be strong enough to overcome the forward impetus of the run and torso press. If it is not, the flight of the takeoff will be too flat (leading to distortions in the execution of the rest of the vault).
    9. Ideally, as the vaulter takes off his/her vision should be focused slightly above vertical. If vision is focused too high or too low at this point, undesirable distortions in the takeoff
flight will occur.
    10. Like many of the best fiberglass vaulters over the last 25 years or so, Vigneron utilizes a pronounced "stiff arming" action with the lower arm as he takes off. Although this action improves his leverage on the pole, it also produces resistance against the "inward" movement of his torso (relative to the pole and the takeoff point). This causes dissipation or loss of "inward" body momentum during the takeoff.
    For optimal results the forward arm as a whole, must be pliable during the takeoff (regardless of the degree of forward arm tension and extension).
    In Vigneron's case the pliability of his forward arm could be much improved simply by narrowing his hand spread a few inches. Note that given sound ex­ecution of the run, plant and takeoff, the vaulter should be able to bend the pole effectively with little or no forward arm pressure / extension.
    11. As with the takeoff, the development of a proficient post takeoff flight path is dependent on correct action and positioning by the vaulter during these phases. For example, in order to achieve vertical flight the vaulter must extend his/her body vertically in line with the pole. Thus the flight path through the vault and the effectiveness of the catapult action are interrelated.
    12. All stylistic variations and all flaws in the execution of the post takeoff phases impact (to varying degrees) the flight of the vaulter and the flow of momentum through the peak of the vault.
    In theory the most desirable stylistic approach to the execution of the post-takeoff phases would promote the most efficient flight path and hence the most efficient flow of momentum in the vaulter's body.
    Although Vigneron's stylistic approach to the execution of these phases is not necessarily ideal in all respects, it is certainly very effective.
    Note that in the source photo sequence, the frame between Figs. 11 and 12 was omitted (the completion of the rock­back). Vigneron typically completed his rock-back with the feet piked back above the top hand, which helps promote the continuous flow of momentum into the vertical extension.
All illustrations by David Bussabarger.

FROM: TRACK COACH 192