The long jump is an athletic (track and field) event where individuals combine speed, strength and agility in order to jump as far as possible in a horizontal direction. The jump itself is broken down into 4 phases (Hay, 1993):
1) The approach
2) The take-off
3) The flight
4) The landing
This analysis will be focusing on the first phase: the approach.
A long-jumper has three primary objectives to execute during the approach run to maximise their jump distance (Hay, 1993): a) to generate the highest amount of horizontal velocity as is possible to be used effectively during the take-off; b) to set-up the position of the body during the final steps of the approach so that it is in the correct position for take-off; c) and to accurately place the foot on the take-off board. These three components are referred to as velocity, position and accuracy (Hay, 1993).
Speed
Definitions:
1. Speed tells us how fast a thing is moving.
2. Velocity is determined by dividing the distance covered by the time taken.
3. Acceleration tells us how fast the velocity of something is changing.
A number of studies (Hay et al., 1986; Hay and Nohard, 1990; Nixdorf and Bruggeman; 1990) have shown a positive correlation between the speed of the approach, or more specifically, the horizontal velocity of the athlete’s center of gravity, and the distance obtained during the long jump (Hay, 1993). As shown in Figure 1.0; a high velocity during the approach results in increased jump length. Ideally, a long-jumper reaches their maximum speed during the last few strides of the run-up (Hay, Miller and Canterna, 1986). Elite male long-jumpers are able to reach speeds of 9.4-9.7 m/s during the middle phase of the approach, and by the fourth to last step of the run reach 10.0-10.1 m/s with a maximum velocity of 10.7 m/s (Hay, 1986).
Figure 1.0
We are able to run forwards because we apply a backwards force against the ground (Blazevich, 2010). Newton’s laws help to explain the relationship between forces and their impact on the individual joints, as well as on the total body in motion.
Newton’s first law, the law of inertia states that: The body remains at rest or in motion except when compelled by an external force to change its state.
Newton’s second law of motion: Acceleration: The acceleration of a body is proportional to the force causing it and takes place in the direction the force acts.
An athlete is overcoming inertia at the beginning of the approach run in long-jump. Their initial acceleration is generated when they exert a force against the ground with their forward foot. The greater the force exerted, the greater the acceleration away from the ground will be( Blazevich, 2010 ). In the approach phase of the long-jump, the athlete wants to generate as much speed as possible through the forces they apply against the ground in order to reach a maximum horizontal velocity which they can then convert to vertical velocity during the take-off to further their jump distance.
To improve running speed we need to understand how to swing our legs more quickly (Blazevich, 2010). In order for an athlete to shift their leg backwards from the front of the body (referred to as the ‘swing phase’) they need to overcome the moment of inertia in the leg (Blazevich, 2010). As Newton’s first law states; an object will remain at rest or continue to move with constant angular velocity providing the net forces that are causing it are equal to zero (Thompson, 1991). The amount of force that is responsible for driving the rotation of the leg is referred to as the ‘moment of torque’; torque can change the rotation of an object at a given moment of inertia by applying linear forces that change the direction movement of the mass/object (Blazevich, 2010). The angular acceleration of the leg is influenced by the amount of torque acting on it and is proportional to the inertia of the leg (Blazevich, 2010). The legs angular acceleration will be greater if the torque is greater, or the moment of inertia in the leg is decreased. Furthermore, if the distance between the muscle and the joint center (called the moment arm) is larger, the amount of torque that can be generated by the leg will be greater.
Unfortunately the moment arm cannot be improved through training (Blazevich, 2010). However, coaches and trainers can work to improve the muscle force of the leg (torque) which will enable the athlete to generate a greater angular velocity of the leg during sprinting and therefore increase the linear speed of the foot (Blazevich, 2010).
Ultimately, this will make it possible for an athlete to reach their maximum velocity during the approach phase and apply this horizontal velocity to the take-off and flight phase during the jump.
Research suggests that athletes reach their maximum speed 6 seconds after the gun is fired, or around the 45-55 meters mark of the sprint (Hay, 1986). Allowing for the fact that long jumpers do not begin their approach in a crouching position and they also need additional 1-2 strides after attaining their maximum speed to set themselves up for take-off, the optimum approach is around 50-60 meters (Hay 1986). This is also governed by the athletes sprinting ability; the faster the athlete, the longer the run-up needs to be to allow them to reach their maximum velocity (Hay, 1986). Athletes must ensure they allow enough distance in their approach to have time to accelerate to their maximum horizontal velocity so that they can utilise that speed during the jump to attain a larger distance.
Newton’s 3rd law of motion, Action and Reaction: "To every action there is an equal and opposite reaction."
A sprinter generates a force against the ground with their foot; this creates an equal and opposite reaction force that moves the body over the ground-see Figure 2.0 (Thompson, 1991). Momentum describes the quantity of motion a body has at a given time, and is a product of weight and velocity. In sport, we often want to change an objects momentum; this is done by applying a force. The greater the force applied, the large the change in the object momentum will be (Thompson, 1991). The longer you apply a force, the more momentum you will transfer into an object (Blazevich, 2010). The relationship between force and time is termed impulse and this relationship is important in the acceleration phase of an athlete during the approach (Blazevich, 2010). Athletes must learn to maximise impulse to change direction of momentum by landing (absorbing the impact) and using this to generate a greater rebound. This is applied to during the sprinting movement so that ground contact is faster and the force applied into the ground is harder to generate powerful explosive movements (Thompson, 1991).
The greater the speed, velocity and momentum impulse a long-jumper generates during the approach run, the higher and longer the trajectory of the centre of mass will be during the take-off phase and the further the distance of the jump will be.
Figure 2.0
Stride Length and Stride Frequency and Accuracy of Approach
Rhythm in the approach run is not only important to achieve the ideal speed at take-off, but it is also imperative to ensure the accuracy in hitting the take-off board (Thompson, 1991). Long-jumpers must execute his or her approach so that they are able to place their final step close to the front of the take-off board (Hay, 1986; 1993).
There have been different techniques observed in elite athletes in association with stride length and frequency during the approach; some athletes gradually increase their stride length up to the moment of take-off, others increase their stride length and frequency up until 7-8 steps within take-off and maintain this control for the remainder of the approach; both techniques seem to produce successful results (Hay, 1986). In Table 1 (a) long-jumpers velocities were recorded at the 4th, 3rd, 2nd and 1st to last steps before take-off. The highest velocities were recorded at take-off of the 2nd to last step and more than half of the remaining athletes maximum velocities were recorded at take-off of the 3rd to last step. Table 1 (b) demonstrates that athletes who reached their maximum velocity during the take-0ff of the 2nd to last stride achieved the greatest jumps (Hay, 1993).
This being the case, it is important that long-jumpers continue to strive to achieve their maximum velocity during the last strides of the approach as this method appears to increase jump distance. However, in a carefully measured approach, increasing stride length to increase an athlete horizontal velocity would place them in the wrong position for take-off. Instead, athletes increase their stride frequency in order to increase their maximum velocity (as mentioned previously), but this method also risk of accumulating small errors during execution of a programmed stride pattern, which could also result in the athlete taking off in the wrong place on the board. What athletes tend to do is use a programming strategy for the majority of the approach, and then use a visual control strategy (by looking up and adjust their last few steps so that they will strike the edge of the take-off board) to guide themselves onto the take-off board (Hay, 1993).
Path of the Centre of Gravity
There are significant changes in an athlete’s centre of gravity during the last 2 strides of the approach (see Figure 3.0); long-jumpers lower their centre of gravity at this time to achieve a higher vertical velocity by lengthening the vertical path over which the athlete can accelerate during take-off (Chow and Hay, 2005).
Figure 3.0
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During those last strides of the approach, it is crucial that the athlete exploits all of the joints available to create optimal force and speed at take-off. These forces from each joint must be combined to produce the maximum effect. This will allow the long jumper to generate the most speed or acceleration out of the approach run (Thompson, 1991).
When several joints are used in a skill, their sequence and timing are important. For example; the most successful movements (in terms of generating force and power) begin with the big muscle groups and move out through the progressively smaller muscles (Blazevich, 2010). This pattern produces continuous flowing movement that allows the separate forces to combine and produce optimum impact. This is called summation of forces, which simply means forces adding together (Blazevich, 2010). Therefore, the take-off velocity of a long jumper depends on their ability to use the principal of summation of forces and transfers these forces as well as their horizontal velocity to vertical velocity at release/take-off.
The Answer
We can now conclude that to maximise the approach technique in the long jump, an athlete must be able to achieve the following;
1) Achieve maximum velocity. Athletes do this by overcoming Inertia of the leg and producing a faster ‘swing phase’ during the run up. To improve this technique, coaches must focus on training the athlete to increase the torque (or the muscle force). Athletes must also learn to maximise impulse in order to change the direction of their momentum during the approach by landing and absorbing the impact of the foot-ground contact and using this to generate a greater rebound.
2) Employ an accurate stride technique. An athlete must calculate their run-up so that they have enough time to accelerate to their maximum horizontal velocity during the approach and simultaneously position themselves in the final strides so that they place their foot accurately on the take-off board at release; a successful approach will incorporate a combination of the programming strategy and the visual control strategy to achieve this.
3) Finally, athletes should try to maximise all the forces produced by their body during the approach and combine these forces through the entire approach, and in particular the final strides, to further their jump distance. This can be done by using joints and muscles in the correct order (i.e. largest to smallest) and ensuring their movement is continuous and flowing. If athletes can achieve this summation of forces during the approach, they can then transfer the force, momentum and horizontal velocity they generated during the run-up to the flight phase of the jump to maximise their distance.
How else can we use this information?
Expert coaches are able to analyse the techniques involved in athletics and modify them to make desired improvements in a particular athlete (Thompson, 1991). Knowledge of the principals that make a successful approach in long-jump can be used to;
1. Introduce children to the sport, or individuals of any age for that matter, who are new to the sport
2. Improve the performance of individuals who are experiencing difficulty with the skills involved with long-jump.
3. Fine-tune elite athletes in their execution of the long-jump to improve their jump distance .
The novice coach often has difficulty deciding which technique to use and what modifications to make; the best place to start, and also the most common, would be to compare the novice athlete with the current world champions by analysing video footage of both and seeing where their techniques differ. The problem that arises is top athletes frequently have different techniques and additionally, coaches and athletes copy bad, as well as good, aspects of each technique (Thompson, 1991). The coach or biomechanisist must do their best to determine each player’s optimum technique through trial and error and determine where their strengths and weaknesses lie. Once these aspects have been determined; coaches can formulate a training regime to improve those particular skills.
The principals of biomechanics that apply to the approach phase of the long jump can also be applied in other sport such as triple jump and high-jump, or any event in sport that involves achieving high velocity and speed in a given period of time.
References
Blazevich, A. J., (2010). Sports Biomechanics: The Basics. London: A & C Black Publishers
Chow, J. W, Hay, J. G (2005). Computer Simulation of the Last Support Phase of the Long Jump. American College of Sports Medicine. DOI: 10.1249/01.MSS.0000150086.13664.32115
Hay, J. G., (1986). The Biomechanics of the Long Jump. Exercise Sport Science Review. 14: pp.401-406. Retrieved From: http://www.tandfonline.com.ezproxy.flinders.edu.au/doi/pdf/10.1080/02640419208729933
Hay, J. G., (1993). The Biomechanics of Jumping for Distance. J. Biomechanics. 26: pp.7-21. Retrieved from: http://www.ncbi.nlm.nih.gov/pubmed/8505354
Hay, J. G., Miller, J. A., Canterna, R. W., (1986). The techniques of elite male long jumpers. J. Biomechanics. 19(10): pp.855-866. Retrieved from: http://www.sciencedirect.com.ezproxy.flinders.edu.au/science/article/pii/0021929086901363
Thompson, P. J. L. (1991). Introduction to coaching theory. International Amateur Athletic Federation. Retrieved from: http://www.coachr.org/biomechanics.htm
