An attempt to coach pole vaulting without an understanding of the underlying mechanical principles has been likened to trying to read without a knowledge of the alphabet. There can be few sporting activities with technique as complex; for by planting his pole the vaulter creates a hinged moment which converts primarily linear motion at take-off into angular motion ; and then, simultaneously and interdependently, one pendulum (the athlete) swings from his hands while a second pendulum (pole and athlete) pivots about the base of the pole.
The good vaulter co- ordinates the timing of these two pendulums.
For by bringing the pole D to an upright position with an inadequate body swing he can never clear impressive heights by modern standards , nor can this be done by swinging past and above the grip with the pole failing to attain a vertical position.
In efficient vaulting the athlete effects a compromise between pole speed and body speed; his grip (always the highest possible under the circumstances) and movements on the pole are designed to project his Centre of Gravity high above his top hand just as the pole reaches an almost vertical position.
However, in gaining this height the expert does more than employ these two pendulum movements. He completes and improves the vault by executing a powerful, carefully-timed and well-directed pulling and pushing action, driving his legs and hips upwards.
Approach speed and height of grip
Although, in good vaulting, little speed is required to clear heights up to 13 ft—and some experts, lacking speed and using a relatively low grip, have gone much higher on their ability to develop a powerful pull-push action—nevertheless speed becomes increasingly important as the bar is raised. illustrates this principle. The speeds shown, expressed in terms of a ‘flying’ 100 yards run at uniform speed, are common to the event.
It has been assumed that all the kinetic energy developed in the run-up can be used in raising the Centre of Gravity (common to pole and athlete) whereas, in fact, some kinetic energy must be dissipated by the impact of the pole with the box, some by the backward thrust of the ground on the athlete’s take-off foot and some by transference of momentum between the pole and the athlete and the various parts of his body; in addition, of course, the vaulter must retain sufficient horizontal speed to cross the bar.
Greater approach speed will enable an athlete to use a higher handhold, provided he has the strength to control the greater centrifugal force of his swing. A flexible pole can be held higher than a stiff one; and his height, weight, spring, skill, the direction and strength of the wind, the run-up surface, his general fitness and motivation—all will influence the height of the vaulter’s grasp on the pole.
Experience proves that, speaking generally, a vaulter should aim for a maximum effective grip (i.e. the distance between the top of his higher hand and the ground when the pole is upright in the box) equal to twice his standing height plus at least 4 in. (at least 12 in., when using a fibre-glass pole). This can then be used with maximum controlled speed at each height (which is recommended) or the vaulter can lower his grip and run slower at the easier heights, progressively raising his grip and increasing his speed throughout a competition.
Some of the pole’s speed, and therefore its kinetic energy, developed in the approach is lost at take-off. The takeoff velocity has been resolved into one component acting beneficially, at right angles to the pole , and another directed through the length of the pole into the box. For a given velocity, the greater the angle between pole and ground at takeoff the more effective will be the approach speed (compare Figs. 149tf and 1496); but, of course, this angle can be too great, leaving little for the pole to do.
The good vaulter does not simply run off the ground into his swing, however. He adds to his take-off velocity (Ganslen estimates by as much as 4 ft per second) and directs it at a more favourable angle by jumping; and this is of particular importance when he holds high and the take-off angle between pole and ground is therefore comparatively small (compare Figs. 149« and 1496). Thus he is able to exert maximum force with his hands at right angles to the pole.
Kinetic energy can be retained as a result of the pole’s flexibility; a good pole will ‘give’ as it takes the vaulter’s weight, first assuming a slightly convex bend away from the athlete and then curving laterally (to the left with a left-footed vaulter, and vice versa).
The loss of kinetic energy can also be reduced through an emphasis on forward-upward as opposed to an upward-forward (i.e. a stabbing) movement in planting the pole. The timing is also important: if it is too late or the take-off is too close (i.e. not directly beneath the vaulter’s hands ) he will be snatched prematurely off the ground. Some of the shock can also be absorbed by a partial extension of the arms (never fully stretched, however) at take-off, and by having sand in the box to ‘cushion’ the impact.
In good vaulting, through a pronounced forward-upward take-off drive, the athlete’s chest contacts the pole early in the swing; first he swings from his hands, therefore, and later from his shoulders.
Just as the arm of a metronome oscillates more rapidly as its weight is moved closer to the fulcrum , so, on leaving the ground, does the expert in this event give speed to his pole by extending his body momentarily, keeping his Centre of Gravity close to the pole’s base. This exemplifies the principle of the conservation of angular momentum , for by reducing the moment of inertia, angular velocity is increased proportionately.
This ‘hanging’ movement, in which the vaulter arches his back ‘letting his stomach and hips out’ (Warmerdam)—and which should always be performed in a vertical plane at right angles to the plane of the uprights—is vital to bringing the pole to the vertical only where the highest grip is used commensurate with take-off velocity. With a lower grip there will be neither the necessity nor time for a ‘hang’.
Again, the ‘hang’ position should never be exaggerated beyond the vaulter’s power, later, to raise and flex his legs against gravity and the centrifugal force tending to tear him away from his grip. This is particularly true of the tall, long-legged athlete whose Centre of Gravity is low relative to his hand-hold; he will develop greater centrifugal force than a shorter man swinging with equal angular velocity, and will therefore require more strength and speed.
Nor should the ‘hang’ be held too long or there will not be time in which to raise and turn the body for bar clearance. On the other hand, if it is too short the reaction to the forces involved later, in raising and pulling the body, will act at an angle to the pole and these movements will increase the horizontal distance between the vaulter and the box— both slowing the pole down.
Obviously the vaulter’s movements affect the radii and, therefore, the speeds of both pendulums. So that in addition to the advantages mentioned, by ‘hanging’ momentarily the vaulter increases the moment of inertia of his body about his grip, reducing his angular velocity and staying behind his pole; for if his Centre of Gravity swings too quickly ahead, the pole will lose speed.
Although there must be an element of compromise in the swing of a good vault, it should always be as long delayed as practicable.
When the vaulter’s trunk has swung so that his Centre of Gravity is approximately in line with the base of the pole and his grip, he is then able to exert force without excessively reducing the pole’s speed.
In the process of conserving angular momentum in the swing he has maintained a low position of his Centre of Gravity; it has little vertical speed. But now he must raise it quickly and adopt a position from which he can benefit from a straightening of the pole and further increase vertical speed by pulling and pushing with his arms and by stretching his body; and, ideally, this must be achieved without permitting his Centre of Gravity to move in front of the base-grip line of the pole.
At this stage therefore, and with the vaulter swinging about his grip again, the good performer reduces the moment of inertia of his body, speeding up and raising his hips and legs while keeping his head and upper trunk behind the pole. His legs, flexed vigorously at hips and knees, are pulled in, while, simultaneously, this is counterbalanced by rocking the head and upper body back from extended arms ‘see-saw’ fashion. At the end of the swing-up, therefore, the vaulter’s back is approximately parallel with the ground, with the line of the pole by the left hip. The movement has been described as the beginning of the pull on the pole. It is a pull through the length of the pole initiated by the large muscles of the back, chest, hip flexors and abdominals, with the weaker but faster arm and shoulder muscles taking up and comple- ting the action later.
In performing his swing-up the vaulter does considerable work, resulting in an increase of rotational kinetic energy about his hands. As centrifugal force is propor- tional to the radius of movement times the square of its angular velocity, centri- fugal force might be increased as a result—which perhaps explains why weak athletes find it difficult to keep the head and upper body behind the pole at this stage.
Inevitably, the swing-up reduces the speed of the pole-athlete pendulum, for it increases the distance between the base of the pole (the fulcrum) and the Centre of Gravity common to pole and man. However, this effect can be minimised through correct timing; but if the swing-up occurs too soon, the pole will not carry the athlete to the bar. As we shall see , the timing of this important phase is partly dependent upon the degree of pole flexibility.
Pull, stretch and push
The speed developed in the approach and take-off cannot be sufficient to project a vaulter to maximum heights, perhaps more than 3 ft above his grip on the pole: he must add to his speed by pulling and pushing with his arms and by stretching the original free leg vigorously upwards.
As in the swing-up, the continued raising of body weight lengthens the pole-athlete pendulum and slows it down; in fact, the pull-stretch phase would eventually stop the pole. Under such circumstances the expert conserves what pole speed he can by keeping his Centre of Gravity in line with the pole throughout, or almost so, as in the swing-up. His body spirals upwards about a near-vertical axis, close to the pole.
In good vaulting the pulling and stretching movements begin as top vertical speed is attained in the swing-up, so that one phase flows smoothly into the next. An early pull will ‘kill’ the pole’s speed, and if it is too late the vaulter will rotate too quickly around the bar, dropping his legs rapidly and landing on his back.
The earliest position from which an effective pull-up can take place, assuming adequate vertical speed; the higher the hips are at the moment of initiating it, the more vertical—and therefore the more advantageous—will be the movements which follow.
Pull and stretch should be simultaneous and their forces directed through the length of the pole towards the ground; the pull should be strong and fast and the free leg should be driven vertically in front of the plane of the uprights.
The turn occurs partly as a result of a scissoring leg action, whereby the original free leg is stretched vigorously upwards (vertically by some, and to the left of the pole by others) while the original take-off leg, flexed, ‘cuts’ behind, turning the hips ; and it is due partly to the position of the hands on the pole one above the other, encouraging a twisting of the shoulders in the direction of the grip. Turning speed is related to pulling speed. (When the hands are close together a vaulter swings more effectively, is less likely to turn prematurely (i.e. he ‘stays on his back’), divides the work of his arms more evenly and is more likely to raise his chest a maximum height above his grip on release than with the hands wide apart, However, a gap of approximately 6 in.—while not sufficient to lose these advantages—also permits the take-off leg to swing past the pole without striking it, provides a more favourable leverage for the lower (usually weaker) arm and gives a better balanced position in the pull-up. When using a fibre-glass pole, the vaulter’s grasp should be wider.)
The push is merely a continuation of the pulling action and, like the pull, should be directed through the long axis of the pole towards the ground, against maximum resistance, with the pole (which would otherwise begin to fall back towards the ground) kept close to the athlete.
At first glance it would seem that all parts of the vaulter’s body, and therefore his Centre of Gravity, should rise at maximum vertical speed until he has released the pole; then, having broken contact, he should ‘jack’ (i.e. flex markedly at the hips) to raise his abdomen in relation to his Centre of Gravity, improving his lay-out. Finally, with his hips clear of the bar, he should ‘unjack’ quickly to clear the head, chest and arms, depressing his abdomen and folding back his legs in reaction.
In practice, however, the vaulter must develop a rotation before release, to assist in the raising of the parts of his body still below the bar, and to land feet first in the pit. This rotation is brought about partly by a transference of angular momentum acquired in dropping the legs slightly, but is due, mainly, to a turning couple created by the reaction to his thrust on the pole, acting vertically upwards ); and the force of his weight, acting through his Centre of Gravity, pulling vertically downwards ).
In efficient vaulting, the force of the pole’s upward thrust always exceeds this downward pull. Therefore, although the forces of the couple are equal the athlete’s Centre of
Gravity continues to rise; he releases the pole rotating but still moving upwards.
In this phase also, therefore, a good vault is a compromise. When they have cleared the bar, the hips ‘break’ slightly and the vaulter assumes an arch position at his high point ; and the slight dropping of the legs (in particular, the original take-off leg) takes weight off the shoulders and arms, making it easier to give vertical speed to the upper body which has still to cross the bar. The extent to which a vaulter drops his legs at this stage depends upon the hip and leg elevation obtained previously in the vault and upon his arm and shoulder power (not to mention his sense of self-preservation!).
The modern vaulter ‘jacks’ only in an emergency for this outmoded technique requires more time over the bar than is usually available. Ganslen estimates average horizontal clearance velocity in good vaulting at 6 ft per second—too great to give sufficient time for ‘jacking’ and ‘unjacking’. (The more efficiently the vaulter converts horizontal to vertical movement, however, the greater the period of time for which he is over—and tending to drop on to—the bar, and the faster and more skilful must be his final movements.)
Again, when a vaulter ‘jacks’, still grasping his pole (and, therefore, still indirectly in contact with the ground), he tends merely to pivot about, and lower his Centre of Gravity, instead of continuing to move it upward. Finally, ‘jacking’ involves too much movement at bar level, with chest and thighs in very close proximity with the bar.
Timing and the pole
The timing of a vaulter’s movements will be influenced by the flexibility of his pole. He depends upon its resistance, and yet, if too stiff, it lifts him too rapidly, particularly when he is gripping high; he has to hurry his movements, tending to attain his high point in front of the bar. Also, he is unable to swing directly forward after take-off and often strikes the pole with the thigh of his jumping leg.
On the other hand, if the pole is too springy its bend has the effect of lowering the hand-hold, reducing the moment of inertia of the pole-athlete pendulum and speeding it up, so that there is insufficient time to complete the lifting movements. It may not straighten out in time to be of benefit to the vaulter, and an early pull may even break it. (Even before the introduction of the fibre-glass pole, poles were known to bend as much as 3 ft out of line, lowering the common Centre of Gravity by as much as 7 in.) (Ganslen.)
A reasonable pole-bend (e.g. of approximately 1 ½ ft to 2 ft out of line) permits the use of a higher grasp than is possible with a stiff pole; it takes some of the take-off shock, allows the athlete’s Centre of Gravity to swing directly forward over the box, permits a comparatively gradual rise in the path of the vaulter’s Centre of Gravity (giving sufficient time for his various movements on the pole) and adds to his vertical speed.
The fibre-glass pole
This gives greater height in pole vaulting because it permits the use of a higher grasp and, in bending markedly, stores more energy than poles used hitherto. However, this energy must be given back to the vaulter—and quickly—at the proper time; he must therefore select a pole appropriate to his weight, speed and hand-hold. Its introduction to modern vaulting has brought about the following modifications to the technique: (a) To bend the pole the take-off foot is placed slightly ahead of a vertical line through the top hand at the instant of leaving the ground, and the athlete drives more horizontally. The pole—not the arms— takes the shock of impact. A wider (1-1 ft) grasp encourages this for, then, the top arm is straighter; it also permits a pushing forward of the lower arm and pulling back of the top arm movements, which immediately establish the direction of pole-bend. (b) To retain, and even add to, this bend the vaulter slightly shortens the swinging phase; he lifts his legs viciously and rocks back sooner, so transmitting a large force through his hands into the pole. His wider grasp gives him greater control at this stage, preventing a premature forward trunk swing. (c) To adopt and hold the best position from which to use the released energy when the pole straightens, the vaulter leads with his take-off leg in the shortened swing to avoid turning prematurely; he ‘stays on his back’, with knees, thighs and hips vertical. However, this is no passive position for, as the pole pivots and then straightens, the tendency is for the legs to be driven down; the vaulter must therefore attempt to bring his feet further and further above his head.