Introduction
The
high jump is a track and field event where an athlete attempts to clear a
horizontally raised bar without causing it to fall off the supporting standards.
An athlete must use self propulsion off one leg to achieve this as stated in
rule 182 of the International
Association of Athletics Federations competition rules for
2010/2011. The high jump is a unique
event as it has undergone large kinetic and biomechanical changes in recent
history (Reid, 1986). This is clearly seen in the development of the Fosbury
flop, which prior to 1968, was but one of the many variations of jumping
technique (Tan and Yeadon, 2005). The flop has become the most recognised style
used by all current elite jumpers and has brought consolidation, specific
scientific analysis and height progression to the event (Schubin &
Schustin, 1993). Collectively known as ‘floppers’, all elite jumpers now follow
this similar jump sequence consisting of a curved approach, the take-off and
the flight in an attempt to maximise the height of the centre of mass to pass
over the horizontal bar without dislodging it from the standards (Isolehto, Virmavirta,
Kyröläinen & Komi, 2007) Although the flop is now considered the favoured
style, variations within the technique do exist. Different jumpers may choose
slight variations of the technique based on their morphological and
physiological characteristics (Reid, 1986). In this discussion I will attempt
to describe the phases of the high jump and the biomechanical and physiological
aspects which will impact on the maximal achievable height.
Maximal
height is achieved by taking the centre of mass through a parabola shaped arch
with the optimal position having the apex pass over the midpoint of the bar
(Dapena, 1995). Body segments move around the centre of mass and can be
adjusted during the flight phase, which is essential in creating the most
efficient position to achieve maximal height (Dapena, 1992). This, along with
the phases preceding the flight determines the success or failure of an
attempt.
The approach
The
approach is the initial phase which precedes the take-off. It consists of the
preliminary, the drive and the curve phases (Schexnayder, 1994). The preliminary phase
normally includes a few steps or a bound but may also be a standing start
(Dapena, 1992). This normally allows the athlete to prepare for a smooth, fluid
approach movement and may also assist in the ritual psychological and mental
imagery preparation preceding each jump (Feltz, & Landers, 1983). The nature of the approach
in high jump is clearly developed by each athlete to achieve consistency
through practice (Patrick, 2001). Deviations, especially in a competitive
environment result in athletes having to make adjustments at later phases which
may negatively affect the desired outcome (Botha, & Potgieter, 1991). As
the height of the bar increases, the pattern of the approach stays the same but
the components will be adjusted.
The drive phase
The
approach phase consists of eight to twelve strides, ignoring the possible
preliminary phase (Tidow, 1993). The purpose of the approach phase is to create
maximal horizontal velocity while maintaining an outward centrifugal force from
the jumper leaning into the curve (Patrick, 2001). This is initiated in the
drive phase by accelerating for the initial three to five steps on a tangent,
normally slightly more than 90° to
the plane of the standards, towards the approach curve (Tidow, 1993). The initial approach should aim to progress
too long relaxed strides maximising acceleration (Dapena, 1992). The approach
phase in high jump has many factors in common with the approach phase in other
horizontal jumps. The drive phase requires the forward leaning posture
progressing to an erect posture (Schexnayder, 1994). Acceleration is described
as change in velocity over time. The nature of high jump allows the greatest
increase in acceleration over the first three to five steps (Blazevich, 2007a)
before entering into the curved phase. Early momentum development is important
in any jumping event. This allows time to focus on correct execution of technical
components in the later phases (Schexnayder, 1994). An impulse is defined as
the integral of a force with respect to time. Higher velocities allow for
shorter ground contact time and hence there is less chance to apply an impulse
later in the approach phase (Blazevich, 2007b). A good driving phase allows for
more ground contact time, creating a greater impulse and this leads to a higher
momentum. This is achieved by strong hip extension using the gluteus maximus
and the hamstrings and knee extension using the quadriceps muscle group. The
drive phase occurs with the foot leaving the ground far behind the centre of
mass and progressively shifts to leaving the ground slightly behind the centre
of mass. Although high jump has this drive phase, it is less noticeable that
other acceleration events but no less vital. The short time to develop the
momentum in high jump is achieved by limiting the forward lean and achieving an
erect posture within about four strides (Schexnayder, 1994). Greater acceleration through the drive phase
allows for a higher approach velocity which correlates to a greater achievable
height (Blažević, Antekolović & Mejovšek, 2006).
The
curve phase
With
early momentum developed, the next part of the approach is the curve phase
which begins when the athlete starts the radial approach and ends at touch down
on the final stride before take-off. It is the curve phase which makes the flop
such an effective style for achieving maximal height (Tan and Yeadon, 2005).
The curve creates a centrifugal force which pulls the jumper outwards, creating
angular momentum which effectively leads to the twisting, backwards somersault
(Dapena, 1995). Higher velocities create a greater centrifugal force; hence a
greater radius can be used for higher approach velocity while still maintaining
the same centrifugal force. Elite athletes normally have a greater approach
velocity which allows them to use a greater approach radius (Schexnayder, 1994). It is easier to maintain
horizontal velocity on a larger radius while maintaining the same centrifugal
force outward (Chang & Kram, 2007). This has been described in indoor 200m
events with the inside lanes being a distinct disadvantage (Usherwood
&Wilson, 2006). A clear correlation between jump height and approach speed
is the horizontal velocity at the penultimate stride (Blažević
et al., 2006).Being
able to maintain a high approach speed positively affects jump height (Isolehto
et al., 2007).
It
is important to maintain as much horizontal velocity during the curve approach.
An impulse can only be created during the stance phases (Tidow, 1993). Higher velocity allows for much greater
inward lean and thus lowers the centre of mass leading up to take-off (Tidow, 1993). At the penultimate stride the bodies centre
of mass should be at its lowest point and at it greatest inward lean (Dapena,
1992). At this point straightening occurs which, due to the conservation of
moment allows for the body to continue moving outwards after take-off. Once
take-off occurs the centre of mass will travel in a straight line (Blazevich,
2007c). The tangent to the curve at the take-off point should be aimed at the
back corner of the pit (Schexnayder, 1994). This should allow the body
enough horizontal energy to pass over the bar, vertical energy to get the
centre of mass to the desired height and angular momentum to allow for movement
around the horizontal and vertical axes (Dapena, 1995). The lowering of the
centre of mass is achieved by lowering the hips during the running phase which
extends the take-off moment allowing for a greater vertical impulse (Tan and
Yeadon, 2005).
The take-off
Energy
can’t be created or destroyed. The energy that the jumper leaves the ground
with cannot change unless acted upon by an external force (Tidow, 1993). Hence creating an amount of angular momentum
prior to take-off is crucial in allowing the athlete to correctly adjust in the
air (Dapena, 1992). Angular momentum is
described as the product of the moment of inertia and angular velocity.
Creating the backward, twisting somersault requires three planes of movement
(Dapena, 1992). The twist which gets the athlete to turn their back to the bar
is achieved by creating rotational momentum through the vertical axis. This is
done by the athlete drawing the lead swing leg across the body and rotating the
shoulders away from the bar during take-off (Dapena, 1995). If this is
correctly achieved the athlete should pass over the bar on their back with the
hips level. An over or under exaggerated twist will cause the jumper to be over-rotated
or under-rotated during mid-flight (Hackett, B. 1989).
Dapena,
(1992) describes the movement which occur in the horizontal plane. The first being the forward somersaulting
angular momentum which is achieve by thrusting the hips forward during the last
stride. As the foot leaves the ground this causes the trunk to rotate forward.
Too much over-rotation is prevented by actions of the leading leg and the arms.
The other plane of movement occurs as a lateral somersault in the horizontal
plane. An athlete taking off on their
left leg has clockwise lateral rotation towards the direction of the jump
running. This in conjunction with the curved run up helps to create more lift
(Dapena, 1992). The higher the angular momentum, the faster the athlete
rotates. The components of the forward and the lateral somersault form the
resultant somersault angular momentum (Dapena, 1995).
The
take off phase occurs between touch down during the final stride until
take-off. The penultimate stride is often included in this phase due to the
high correlation of jump height and the results of this stride (Blažević et al., 2006).
The height of the centre of mass is dependent on the ground reaction forces
created during this take off stance (Dapena & Chung, 1988). Throwing the
arms upward during take-off does not only control the angular momentum but also
affect the muscle contraction velocity (Harman, Rosenstein, Frykman & Rosenstein, 1991). It has been shown that
muscle force capacity decreases as the contraction velocity increases. When the
arms are swung upward this exerts a downward force on the body forcing the hip
and knee extensors to slow down thereby creating a higher force which is
sustained over a longer period of time (Harman, et al., 1991). By lowering the hips in the
penultimate stride, the athlete is effectively prolonging the impulse period
again allowing for greater force generation (Isolehto, et al., 2007).
To
maximise the jump height, an athlete can rely on certain muscle physiology to
aid in achieving this goal. At touch down on the final stride the quadriceps
and gluteal muscles are eccentrically loaded. This mechanism is called the
stretch-shortening cycle, which has been extensively studied in activities such
as plyometrics (Reid, 1989).
Although the physiology is not entirely clear, it is likely to involve either
mechanical loading of the series elastic component in which the
musculotendonous unit releases stored elastic energy and or a combination of a
neurophysiological model which involved the activation of the spindle fibres
allowing for maximal recruitment of the muscle fibres following a stretch relax
(Wilk, Voight, Keirns, Gambetta, Andrews & Dillman, 1993). Due to the nature of this system, if
the athlete is overloaded where the applied forces are too great or the muscles
are unable to effectively utilise the potential energy due to weakness or
instability, the stored energy will be lost and the athlete will not benefit
from this mechanism (Potach & Chu, 2008). High vertical velocity at the end
of take-off has a high correlation to jump height (Blažević
et al., 2006).
This mechanism also improves with practice as neural firing become more precise
(Wickham-Bruno, & Escamilla, 2007).
Take
off distance is another variable which needs to be consisted. There may not be
an ideal distance but there is certainly a distance which allows for greatest
success for each individual during a jump (Dapena, 1992). Many factors
contribute to the final take-off distance but if the jumper is too close to the
bar they will hit the bar on the way up. If however they are too far away from
the bar they will likely come down on the bar (Hackett, B. 1989). Ideally the athlete would
like to have the centre of mass pass over the bar in the middle. Athletes can
make minor corrections during the run up called steering (Schexnayder, 1994). If however the lean angle
is too steep or the approach is too quick the take-off distance needs to be
further away from the bar to allow the centre of mass to reach maximal height
directly above the bar or visa versa.
The flight
An
efficient jumper should be able to pass their centre of mass over a height
slightly higher than the path of the centre of mass (Dapena, 1992). This is
achieved by moving segments of the body around the centre of mass to allow the
part passing over the bar to be at the highest position. As the head passes
over the bar the jumper extends the neck and extends the hips lowering the
upper and the lower segment. This in turn raises the middle segment high enough
to pass over the bar. As it passes over, the hips are flexed and the knees
extended lowering the middle segment and raising the lower segment (Blazeveich, 2007c).
The principle concerns the conservation of energy. One segment cannot go higher
without another segment going lower. In a similar way adjustments in the air
can be achieved by speeding up or slowing down the rotation of one part to slow
down or speed up the rotation of another part (Dapena, 1992).
Local
and global muscle control is vital in achieving maximal height. Without good
control of the core and the pelvic muscles the athlete would not be able to
extend the hips effectively and allow the centre of mass to pass over the bar;
and flex the hips to allow the legs to follow the same path (Elphinston, 2008).
If an athlete lacked gluteal strength, they would find themselves sitting in
the flight and not be able to raise the centre of mass leading to an
inefficient clearance (Patrick, 2001).
It
is also worth considering that during a competition, athletes may be required
to complete multiple jumps. To maximise the potential to achieve a high
finishing position, an athlete may start well below their potential. Athletes
are allowed 3 failures at each height before elimination. This requires athletes to conserve energy to
achieve the potential improvements in later stages. This needs to be assessed
and managed through competition preparation and training techniques.
Conclusion
The
high jump is a complex event which requires technical efficiency to maximise
the achievable height. The phases can be described using the principles of
physics. The approach uses acceleration, ground reaction and centrifugal
forces. The take-off utilises angular momentum and vertical displacement and
the flight follows torque and movement around the centre of mass. These along
with physiological principles and muscle mechanics combine to achieve a
successful jump and achieve maximal height.
Reference list
Blazeveich, A. (2007a).
Position, velocity and acceleration. In: Sports
biomechanics. The basics: optimizing human performance, (pp. 1-14). London.
A&C Black Pub Ltd.
Blazeveich, A. (2007b).
The impulse – momentum relationship. In: Sports
biomechanics. The basics: optimizing human performance, (pp. 49-60).
London. A&C Black Pub Ltd.
Blazeveich, A. (2007c).
Torque and centre of mass. In: Sports
biomechanics. The basics: optimizing human performance, (pp. 61-70).
London. A&C Black Pub Ltd.
Blažević, I.,
Antekolović, L. & Mejovšek, M. (2006). Variability of high jump kinematic
parameters in longitudinal follow-up. Kinesiology,
38, 63.
Botha,
H. & Potgieter, G. (1991). Athletics 2000. A manual for athlete and coach. (1st ed.). Goodwood:
Tafelberg.
Chang,
Y.H. & Kram, R. (2007). Limitations
to maximum running speed on flat curves. The Journal of Experimental Biology. 210, 971-982.
doi:10.1242/jeb.02728.
Dapena,
J., & Chung, C.S. (1988). Vertical and radial motions of the body during
the takeoff phase of high jumping. Medicine and Sports in Exercise, 20, 290-301
Dapena, J. (1992). Biomechanical studies in the high jump and the implications to coaching. Track & Field Quarterly Review Winter,
92, 34-38
Dapena, J. (1995). The rotation over the bar in the Fosbury-flop high jump. Track Coach Summer, 132, 4201-4210.
Elphinston, J. (2008). Stability, sports and performance movement
(1st ed.). Chichester: Lotus publishing
Feltz, D.L. & Landers, D.M. (1983). Effects of mental practice on motor skill learning and
performance: a Meta-analysis. Journal of
Sport Psychology, 5, 25-57
Hackett,
B. (1989). Analysis
of the high jump crossbar in failed attempts. / Analyse des
chutes de la barre en saut en hauteur. Track
Technique Spring. 107, 3409-3411.
Harman,
E., Rosenstein, M., Frykman, P. & Rosenstein, R. (1991). The effects of arms
and contermovement on vertical jumping (Le role des bras et les effets d'un
contre-mouvement lors de la detente verticale). National Strength & Conditioning Association Journal. 13,
38-39.
Isolehto,
J., Virmavirta, M., Kyröläinen, H. & Komi, P.V. (2007). Biomechanical analysis of the high jump
at the 2005 IAAF World Championships in Athletics. New Studies in Athletics, 22, 17
Patrick,
S. (2001).High
jump: technical aspects. /
Saut en hauteur: aspects techniques. Track
Coach Spring. 155, 4938-4940.
Potach,
D.H. & Chu, D.A. (2008). Plyometric
training. Baechle, T.R. & Earle, R.W. Essentials
of strength training and conditioning. (3rd ed.), (pp. 413-456). Champaign:
Human Kinetics.
Reid, P. (1989).
Plyometrics and the high jump. / L' entrainement pliometrique et
le saut en hauteur. New Studies in
Athletics. 4, 67-74
Schexnayder,
I. (1994).Special considerations for the high jump
approach. / Considerations speciales pour l ' approche du saut en hauteur. Track Technique Winter, 126, 4029-4031.
Schubin,
M. & Schustin, B. (1993). Approaching heights - some model parameters of the high
jump. Modern Athlete & Coach,
31, 31-33.
Tan,
J., & Yeadon, M.R. (2005). Why do high jumpers
use a curved approach? Journal of Sports
Sciences, 23, 775-780
Tidow, G. (1993). Model technique analysis sheeets. Part VIII: the flop high jump. /
Schema analytique du modele technique du Saut en Hauteur (flop). New Studies in Athletics, 8, 31-44.
Usherwood,
J.R. &Wilson, A.M. (2006). Accounting for elite indoor 200 m sprint results.
Biology Letters. 2, 47–50.
doi:10.1098/rsbl.2005.0399.
Wickham-Bruno,
R. & Escamilla, R.F. (2007). Exercise-based conditioning and
rehabilitation. In: G. S. Kolt, & L. Snyder-Mackler (Eds.), Physical
therapies in sport and exercise (pp. 149-170). Edinburgh: Churchill
Livingstone
Wilk,
K.E., Voight,
M.L., Keirns,
M.A., Gambetta,
V., Andrews, J.R. & Dillman, C.J. (1993). Stretch-shortening drills for the upper extremities: theory and clinical application. Journal of Orthopaedic & Sports Physical
Therapy. 17, 225-239.
By: N.Brink
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