Maximizing Energy in the Pole Vault

Transcription

1 Maximizing Energy in the Pole Vault By Spencer Chang, MD University of Hawaii Pole Vault Coach Orthopedic Surgeon Sports Medicine/Foot and Ankle Surgery Introduction Performance in the pole vault is determined by efficiency of movements that will optimize transfer of energy in a vertical direction. For example, one might be fast down the runway, but inefficiency in the plant will result in slowing down at the most critical point, the take-off. We know from Adamczewski and Dickwach, as well as McGinnis s work that fast approach velocities particularly from 10 m to 5 m from the plant box are necessary to vault high. However, there are numerous components of the vault, which may result in a loss of velocity, or conversion of energy to a vertical direction. The purpose of this paper is to explore concepts that will help our vaulters maximize efficiency of energy transfer in the pole vault. The techniques described in this article are for right-handed vaulters. The Pole Carry According to the Petrov model, the hands should be held at a width that would be comfortable hanging from a horizontal bar. This is approximately shoulder width apart. It is also easier to swing while hanging from this position. While dangling from a horizontal bar, the distance from the hands to the feet is at its longest when held at shoulder width apart as opposed to wider than shoulder width apart. Therefore, extension at the plant is optimized with a shoulder width pole carry. This width also allows the vaulter to adequately balance the pole such that the right hand does not drift too far behind the vaulter s back, and maintenance of a high pole carry (right hand around the waist level) can be accomplished. By doing so, positioning of the upper extremities is similar to a sprinter. Some coaches advocate the use of a wider than shoulder width pole carry. The pole may be easier to carry, particularly for heavier, longer poles. Proponents suggest that this allows positioning of the bottom arm such that there is a mechanical advantage in initiating the pole bend. With a properly executed plant (both arms extended upwards) and take-off, it is the speed and momentum of the vaulter that causes a bend in the pole. Coaches should de-emphasize using the left arm to bend the pole and never suggest pulling down with the right arm. One must remember that with a wider grip, maintenance of a straight left arm after take-off may result in blocking the shoulder s forward motion and retarding the swing. 1

2 The Approach and Pole Drop In reality, the pole drop starts at the initiation of the approach. In order to maximize efficiency of movement to increase speed, the vaulter needs to eliminate excessive counterproductive motion, yet should neither be rigid. Just like a sprinter, the vaulter needs to use reciprocal motions to maintain balance. As the sprinter drives the right knee with hip flexion, knee flexion, and ankle dorsiflexion, the left hip extensors, knee extensors, and ankle plantar flexors push the athlete forward. At the same time, reciprocal motions in the upper extremity allow balance and rhythm. Shoulder extension and elbow extension (the driving back motion of the upper extremity) coincide with the opposite lower extremity extensors (the pushing forward motion). One needs to keep in mind this reciprocal motion concept during the pole vault approach. Therefore, as the right knee drives, to balance and reciprocate that motion, the left shoulder and upper extremity move forward slightly and vice versa. Now to optimize pole carry, the vaulter needs to eliminate a swinging, up and down motion, of the pole. Allow the upper limbs to move in reciprocal fashion, however, maintain a steady pole drop. This means that the movement of the hands is relatively minimal except to allow the pole to drop. It is important to have a high pole carry, i.e. holding the pole such that the right hand is around waist level with the elbow bent, and the left hand is held at chest level. The left hand should be placed to support the pole with a cocked up wrist, and elbow pointing downward, keeping it close to the chest wall laterally. The pole drop is more right arm dependent. An attempt should be made to lower the pole by raising the right hand up, staying close to the torso, and maintaining the position of the left hand. An upright stance is necessary to stay balanced, accelerate down the runway, drop the pole efficiently, and to be able to jump off of the ground. The shoulders should be relatively square, or perpendicular to the runway, allowing for reciprocal movements to coincide with each stride. An efficient pole drop will fall at the approximate rate of the acceleration of gravity. This will effectively make the pole weightless. A perfectly timed pole drop can therefore be accomplished with just the top hand. Timing the pole drop as such will help to accelerate the run and increase the cadence of the last few steps. If the vaulter is forced to hold the pole tip up, the pole becomes mechanically heavier as the pole drops to a parallel position. This forces the vaulter to lean backwards, decreasing efficiency of the run, and places the vaulter in a poor position to jump off the ground. Timing the pole drop will need to be individualized per vaulter. This will depend on the vaulter s speed, height, and length/weight of pole. Counting backwards with the take-off step being #1, Sergei Bubka held his pole at approximately 80 through the #7 left step, then proceeded to drop the pole in the following manner: #6 left step ~ 75 2

3 #5 left step ~ 65 #4 left step ~ #3 left step ~ 30 #2 left step ~ Parallel to the ground An efficient drop for most vaulters will be quite close to these parameters especially at the #3 and #2 left step. To maintain consistency on the approach, the vaulter should count the left steps backward towards the pit. Moreover, on a shorter approach, the pole should start at the appropriate angle of carry at that particular step. Coaches will use a mid-mark at the #4 or #3 left step to evaluate the vaulter s run and timing of the pole drop. For instance, if the pole is at 50 on the #3 left step, chances are that the pole drop will be late or forced (shoved to the plant position). Within the last 4 left steps, there will be a certain amount of steering. Using the mid-mark, in combination with a take-off step, the coach can make educated adjustments at moving the vaulter in or out at the starting step. For instance, if the vaulter s mid-mark is on or out, but the take-off step is under, chances are that the vaulter is striding out in the last 4 left steps. The mistake in this situation would be to move the vaulter s step back based on the take-off step alone. The Run Top sprint coaches such as Tom Tellez, Dan Pfaff, and Ralph Lindemann describe the goal of a sprinter as being one of pushing rather than pulling with the lower extremities down the track. The pole vault is no different. In order to accomplish this, the vaulter needs to push off the ground under the center of mass (COM). Coach Lindemann has a wonderful article in the Pole Vault Standard, Winter 2003 where much of this is derived. Maintaining an upright posture is extremely important in the pole vault. Keep the head and eye level parallel to the ground. Bubka s initiation of his run starts with his left foot forward and the pole raised to 80. He rocks his weight onto his right foot without shifting his left foot and uses a slight lean forward to give horizontal displacement to the COM. The start of the run should be considered a power run. Eliminate skips and hops to begin the run and remember to start the same way every time. A rhythm of the run should coincide with the pole drop. Brian Yokoyama describes the approach as starting as a power phase transitioning to a power-speed phase, and culminating in a speed phase. The cadence of the approach should gradually increase with the last three steps being the quickest of the approach. Coach Lindemann describes two phases, the acceleration phase and the transition phase. During the acceleration phase, the chest is kept up, with the hips underneath the torso, the knees are driving up, the toes and ankles are dorsiflexed, and the heels are kept up with a high heel recovery. Ground contact is made slightly behind the COM, as power is generated from extension from the hips, knees, and ankles. 3

4 The transition phase starts at around the 4 th left step out where the pole is approximately at 45. The posture is more upright, ground contact time decreases, heel recovery is higher, and power is generated in the hip flexors and knee. The ball of the foot now strikes slightly ahead of the COM. However, importantly, the heel strikes the ground for an active landing. This occurs under the center of mass, allowing the vaulter to continue pushing forward, reacting against the ground. Coordination of the pole drop is the key to maintaining adequate posture. If the vaulter is leaning back, it is often because the pole has been lowered too soon. This will cause a deceleration at take-off. If the vaulter leans too far forward, this displaces the COM forward often causing the vaulter to stride out, lose speed prior to take-off, and step under. The Plant and Take-Off According to Alan Launder, the pole drop starts 3 1/2 steps from take-off (Figure 1). This means that as soon as the 2 nd to the last left step touches down, the vaulter should initiate the pole flip. Think of the 2 nd to the last left step as the UP step (Figure 2). On this step, the vaulter should raise the COM upwards, stay tall, and keep the chest up. Simultaneously, the hands rise with the pole flip allowing the pole to reach a parallel position to the runway. As the hands rise up, the right knee rises as well. Figure 1. Initiation of flip, 3 1/2 steps out. Figure 2. Up step. Right knee driving, right elbow back, torso with reciprocal rotation. Pole flip. Remember not to lower the left hand to plant. Instead with a pole flip, the vaulter will be able to continue an upward motion of the hands. The flip rotates the pole 180, so that the bend line is appropriate at take-off. This is right hand controlled as the vaulter flips the palms under the pole and rotates the arms with the elbows pointing downward. The right hand rises up along the side of the head, and the forearms start to form a triangle viewed from the side (Figure 3). To prevent from a roundhouse plant and to maintain the pole in a central position, allow a reciprocal motion of the shoulders. So, as the right knee drives forward, the right 4

5 shoulder rotates backwards as the pole is kept as close to midline as possible (Figure 2). The shoulders will return to a square position once weight shifts to the right step or penultimate step. The 2 nd to the last stride is slightly longer and the last stride shorter. The trick step or penultimate step is done with a flat foot, preparing the take-off step so the vaulter jumps off of the ground (Figure 3). The trick step is a natural motion to jump off of the ground from one leg. It is similar to the last three steps prior to a slam-dunk jumping from the free-throw line, or a long jump (although not as pronounced). The difference is that the plant timing will often determine the cadence of the steps, and speed of the last step. If the pole is not in a ready position, i.e. pole flipped up with the right hand near the ear on the penultimate step, the vaulter will either slow the last step down to make the plant, or have a late plant. Therefore, plant positioning and timing is important in obtaining an adequate trick step and jump off of the ground. Like a sprinter, the vaulter must move his arms to speed the cadence of his steps. Figure 3. Penultimate or trick step. Figure 4. Take-off step. Arms extended, pole in box, but not at the back of the box yet. As the take-off step touches the ground, the pole should be in the box but not at the back of the box just yet. The arms should be raised overhead as the vaulter initiates the jump at this point. Simultaneously, as the pole tip touches the box, the arms must be completely extended. If the tip touches the box before the arms are extended, the tip will contact the back of the box too soon, jamming the plant. An adequate take-off position is one where a plumb line dropped from the top hand lies just in front of the toes of the left foot. The goal is to start the jump before the pole hits the back of the box. At full extension off of the ground, i.e. the vaulter s arms, body, and legs are extended and pushing off the toes, the pole should not be bent, but should just have contacted the back of the box. This is called a free take-off. Some vaulters do a pre-jump in which the vaulter actually travels a distance before the pole hits the back of the box (Figure 5). The pre-jump requires tremendous long jumping ability. Theoretically, the loss of vertically directed energy is less, as the transference of energy to the pole is not immediate. However, it requires more energy to travel in a horizontal direction as the distance to travel towards the pit is greater. This is a technique impossible to do in the vaulter who does not jump off of the ground. In fact, the vaulter will actually sink in this scenario. 5

6 Figure 5. Pre-jump. Distance traveled before pole contacts the back of the box. Efficient Transfer of Energy at Take-Off It has often been stated that the vaulter should push his/her pole to vertical at take-off. To rotate the pole to vertical, the ideal angle of energy transfer would be perpendicular to pole. However, in order to minimize the energy required to push the pole to vertical, the vaulter must maximize the angle at take-off. Therefore, it is not practical to vault with a take-off perpendicular to a straight pole as this lessens the angle at take-off. To push the pole to vertical, it requires two components, a vertically directed force and a horizontally directed force. The culmination of forces results in a trajectory of approximately 18 in ideal vaults. The key is maximizing vertical velocity without compromising horizontal velocity. This can be done by: 1. Having an up step, trick step (penultimate step), and jump off the ground at take-off. 2. Correct plant timing. 3. Having a take-off step that is at or slightly behind a plumb line dropped from the top hand. 4. Initiating the jump before the pole hits the back of the box. 5. Having an extended position at take-off. 6. Staying rigid with the right shoulder such that the angle between the right arm and torso remains 180. The shoulder must be tensed at take-off. Also, 6

7 maintain rigidity of the back. Not only is this a better plant and take-off technique, it will prevent shoulder and back injuries. 7. Pushing the left arm up (180 to the ground) with a straight arm after take-off (Both arms extend upwards). 8. Jumping up and not under the pole. a. Bring the right heel to the buttock with a dorsiflexed ankle (Figure 4 Position). The drive knee is directed up. b. Don t allow the right foot to pass the plane created by the right arm and torso. c. Don t collapse the left arm at take-off. This will cause the vaulter to rotate towards the pole. 9. Relaxing the lead knee (straighten the knee slightly) after the initial knee drive, keeping the right foot in theplane of the top arm and torso (Figure 6). In other words, drop the right foot from the Figure 4 Position straight down. This will prevent premature rotation of the vaulter towards the pole at takeoff. Even Bubka did this to a certain extent. Note the transition from a swing to a rock back is slower with a double leg swing. The vaulter can minimize this slower transition by driving the knee a second time, simultaneously with the trail leg swing. 10. Maintain a perpendicular torso to the ground. Figure 6. Relaxing the lead knee. 7

8 As soon as the pole hits the back of the box, the pole directs a force on the handholds that causes rotation of the vaulter towards the pole. By using the described techniques, the vaulter can prevent excessive rotation after take-off until maximum vertical rise from the jump is achieved. An efficient take-off can be determined by the angle of the torso in relation to the ground at maximum knee drive. The more perpendicular the torso is to the ground, the more the vaulter maintains vertical velocity and is able to push the pole to vertical (Figure 7). The less perpendicular the torso is to the ground, the greater loss of vertical velocity, and the more the vaulter is positioned in a pulling position horizontally, rather than pushing vertically (Figure 8). The result is a low and often excessive bend in the pole, which will be less dynamic and often stall to vertical. A notable compensatory reaction to this position is a bent trail leg, or an exaggerated C position. Figure 7. Perpendicular to ground. Figure 8. Less than perpendicular to ground. Remember, a less than ideal take-off trajectory may be the result of multiple factors. The vaulter may indeed be jumping, however loses vertical velocity by factors such as a collapsed left arm, a reaching, sometimes kicking right foot (past the plane of the torso), or an excessive C position. It s like trying to dunk a basketball while rotating backwards. The vaulter must maintain a relatively upright position through the vertical rise of the jump. The Swing (Figure 9) A common question asked is, When do I initiate my swing? Assuming that the vaulter has planted with straight arms (such that the left arm is 180 to the ground as if hanging from a horizontal bar), and has maintained an upright position through the vertical rise of the jump, the vaulter will be pushing the pole until the vertical velocity of the jump has reached zero, or the end of the follow through phase. As long as the vaulter is pushing the pole upwards, there is no weight supported by the pole. When the rise stops, a support phase starts. The instant when the vaulter feels support by the pole is when the swing should start. On a properly executed plant, take-off, and follow through, this occurs very shortly after take-off. There should be no hang or passive period, but continuous follow through motion. When vaulting with a straight pole, the support phase is much more obvious. An Oregon stall will also help the vaulter to feel this support phase. 8

9 If the vaulter loses the upright position by rotating towards the pole at take-off, a pulling action in a forward direction is created, and the support phase on the pole is initiated sooner. In this situation, vaulters will often lose penetration into the pit, and have often been told to hang and not swing too soon to prevent this. My definition of the swing is the period after take-off in which the vaulter aligns the top arm with the torso, right foot (may be slightly in front of this plane), and trail leg so that a straight line is formed from the top hand to the left foot. The trail leg is swung to this point, which forms a line pointing from the top hand along the trail leg towards the buttplug of the pole. It s similar to swinging on a horizontal bar if one uses a shoulder width grip. The weight of the vaulter is shifted onto the right hand, as the angular velocity causes a centrifugal force, keeping the pole bent, and aiding in horizontal translation into the pit. It is important to at least keep the trail leg straight throughout the swing. Many vaulters will use a double leg swing by keeping the right knee relatively straight. This lowers the COM, creating a greater COM radius, and therefore larger centrifugal force. If the vaulter uses a double leg swing, there should be an initial knee lift at take-off, followed by a relaxed right knee, and second knee drive simultaneous with the trail leg swing. Figure 9. The Swing The Rock-Back and Row to a Handstand Once a straight line is achieved from the top hand to the left leg, the swing is completed. This is similar to the swing to an extended position achieved in a kip on the horizontal 9

10 bar prior to bringing the feet up towards the bar. At the end of the swing, the vaulter transitions to an inverted position by rotating the shoulders to move the arms forward and up while simultaneously flexing at the waist, and driving the right knee towards the chest. Dave Butler recently submitted an article titled, To Row or Not to Row? A Question of Direction of Pressure. I concur completely with his article. However, I do like to use the term row as it suggests that the arms are maintained in a straight position, and it suggests that the shoulder motion does not stop once the angle is closed off between the arms and the torso or the torso and pole. The importance is the timing of the row, and the balance of the vaulter. Too much rowing pressure too early prevents a swing as one cannot swing with a shoulder to torso angle less than 180 degrees. The elastic motion of the shoulders is key to remember in the vault. The shoulders are loaded up at take off in a stretched extended position. This stimulates a stretch reflex, which allows the vaulter to react to the pole and straighten out to form a straight line during the swing between the right arm, torso and trail leg. The shoulder motion should be continuous as the vaulter inverts. As the angle closes between the arms and torso, the pressure should be matched so that it doesn t impede the inversion motion. Therefore, the rowing motion and inversion motion are coupled to balance each other out with equivalent forces. The inversion motion is dependant on how well the swing was performed. Greater momentum from a proper swing, allows the vaulter to invert more efficiently. Therefore, an improperly coupled row can result in premature unbending of the pole and an inability to become inverted. A gymnast who rows on a horizontal bar but does not invert at the same time does an uprise or a kip. The gymnast who rows and inverts at the same time does a pull-over. The balance of the vaulter is maintained as long as the COM is maintained within the vertical plane of the handgrips. In order to maintain this balance, so that the left shoulder stays within a plane underlying the left hand, the first angle to visibly close to zero degrees will be the angle between the left arm (shoulder to elbow) and torso (Figure 10). The elbow will have to bend in order for this to be achieved. However, it doesn t need to be sucked in or flexed much more than 90 degrees. The vaulter forms a basket type of position getting to this point. Here, the vaulter drops the left shoulder back as the rotational velocity with the shoulders continues, and the body and legs straighten up along the line of the pole. It is extremely important that as the left shoulder is dropped down towards the ground that the vaulter rotates simultaneously with a quarter turn (Figure 11). If both shoulders drop back equivalently, the vaulter will have difficulty turning. If the vaulter does not turn while straightening during the inversion phase, the rotational motion created by the shoulders will stop, and will not continue to a handstand. Moreover, if the turn is initiated too late, the vaulter will fall out of an inverted position and Flag Out. The vaulter should continue a rowing motion, directing the right hand past the right hip while straightening to a completely inverted position. The arms should follow through while rotating another 1/4 turn to complete the row to a handstand. The shoulder motion starting at take-off and 10

11 completed after reaching a handstand should rotate through 360 degrees, coupled with 180 degrees of turning (rotating around the pole). Shoulder motion does not stop after having closed the angle between the torso and arms. Instead, the shoulders should be active throughout the entire vault. With active shoulder motion using both arms, more weight will be shifted to the bottom arm, causing the pole to act like a stiffer pole. This technique is better accomplished by not flexing the left elbow much more than 90. Likewise in the push off phase, the right elbow will not flex much more than 90. Constant motion with the shoulders will continue to load the pole as the vaulter rows to a handstand (Figure 12). The last part of the vault has often been termed the pull, turn, and push. I prefer the row, rotate, and fling. Continuity of shoulder motion, coupled with inversion motion, will produce a more fluid and dynamic vault. Positioning along the pole is also important. The vaulter attempts to align the body and legs with the pole while becoming inverted. Balance is the key factor. The vaulter must remain rigid, to minimize deviation away from the pole. The vaulter can drift away from the pole towards the pit. This is termed passing the pole. The vaulter can also drift in a lateral direction away from the pole. In either case, the top end of the vault will not be as dynamic. Figure 10. Angle closed between left arm (shoulder to elbow) and torso. 11

12 Problems with Getting Inverted In order to swing, the left arm needs to point upwards perpendicular to the ground after take-off. If the angle is more acute, it serves to block the swing, unless the left elbow bends (allowing the left shoulder to lie under the left hand). If the left shoulder lies in a plane behind the left hand, the rock-back becomes very difficult. A wider than shoulder width grip may force hyperflexion (past 180 ) of the right shoulder, and/or a slight bend in the left elbow to allow positioning for a swing (the left shoulder must lie in a plane directly under the left hand). The centrifugal force created by the swing helps to keep the pole bent so the vaulter can become inverted during the rock-back. If the vaulter s take-off angle is such that the torso is not perpendicular to the ground, there is less room to swing. The pole will start to straighten sooner. In this situation, the vaulter must collapse the left elbow to become inverted in time. Since the pole rotates to vertical in the opposite direction that the vaulter is rocking back, it becomes more difficult to rock-back once the pole starts to straighten. If the vaulter can get the feet and hips up over the right hand before the pole starts to straighten, the vault will be more dynamic. Vaulters may have difficulty with inversion in a timely fashion. Tucking the trail leg through (after keeping the leg long for the swing), then straightening the legs once the feet are up will speed up this process. However, there is less angular momentum with a tuck than with keeping the trail leg straight throughout the inversion process. If the latter can be done quickly enough, the vault will be more dynamic. Inversion is best achieved with rotation. Many vaulters have difficulty turning because they start to rotate too late. If the pole has straightened before the vaulter has started to rotate, the vaulter will either go over the bar on his or her back, or drop away from the pole while turning ( flagging out ). When the vaulter rotates while inverting, it prevents passing the pole, and allows a continuous row of the arms to fling the vaulter to a handstand. This is similar to a free or clear hip circle to a handstand in gymnastics. Figure 11. Inversion with rotation. Left shoulder drops down with the turn as the shoulders row through (right hand past the right hip). 12

13 Figure 12. Row towards a handstand. The Fly-Away The key to a successful flyaway is: 1. Don t drop the feet too soon. 2. Don t hold onto the pole too long. 3. Rotate around the bar. 4. Raise arms, head, and torso up. 5. Don t allow the elbows to knock the bar down. 6. Don t thrust the chest into the bar. Standard Settings With a correctly executed vault, the standards need to be set at least 20 (50.8 cm) back. I prefer to have the standards set between cm, but tend to set them closer to 80 cm. Conclusion Improvements in the pole vault will only come by thinking outside of the box. We need to look at our technique and refine it. The USA has the talent to have 20 vaulters for men, and 17 vaulters for women. I hope this generates a healthy discussion on pole vault technique and further stimulation to improve upon what has been the status quo. 13