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| Nate Robinson vs Yao Ming (NBA, 2007) |
When
one thinks of the genetic makeup of a professional basketball player, they
often stereotypically think of an athlete who is of extreme height and trim
muscular build. This is not far from reality. The 2007/08 NBA player survey for
height stated that the average height for players was 6 feet 6.98 inches or
200.6cm. Compare this with the average height of an Australian male which is
175.6cm (ABS, 2012) and it becomes painstakingly clear why basketball is deemed
to be a tall man’s game.
There
is however a vast differential in players heights from tallest to shortest
within the NBA. In 2007/08 the tallest player in the league was Yao Ming who
stood at a towering 7 feet 6 inches (228.6cm) whereas the shortest player, Nate
Robinson stood at 5 feet 9 inches (175.26cm) which is a gap of 53.34cm. In
seems inconceivable then a player of Nate Robinson's height would be able to
defend player of Yao Ming’s stature and block his shot, but it did happen.
What factors do we have to optimise
to maximise jump height?
Maximal
jumps aim to cover the highest vertical and/or horizontal distance from a large
acceleration of the body during one quick legs extension (Samozino, 2010). In
order to comprehend how Nate was able to jump to such a height in which he was
able to successfully block Yao’s shot it is necessary to understand the
biomechanical principles behind the task of jumping. The biomechanical
principles of jumping can be best explained using Newton’s three laws of motion
and law of gravitation.
Newton’s First Law (Law of Inertia)
An object will remain at rest or
continue to move with constant velocity as long as the net force equals zero.
Inertia
is the resistance an object has to a change in its state of motion. All objects
with a mass have inertia which is proportional. The larger the mass of an
object the harder it becomes to change the objects state of motion (Gagan,
2008). The greater the mass the more difficult it becomes for an object to
speed up, slow down or change its direction (Blazevich, 2012). Therefore it
appears that a person who is of shorter stature (who ultimately will more than
likely be of less mass) will find it easy to change from their state of rest to
vertical motion (jumping) than a larger individual. To better understand this
Newton’s second law needs to be explored.
Newton’s Second Law
The acceleration of an object is
proportional to the net force acting on it inversely proportional to the mass
of the object: F=ma.
In
order to change the state of motion of an object a force (N) needs to be
applied. Force = mass x acceleration (F=ma) clarifies that the lighter an
object the faster it will accelerate along with requiring less force to cause
said acceleration. In the above case a smaller individual can accelerate their
body greater under a given force. In order to accelerate an object faster a
greater force needs to be applied to it. Newton’s third law will help to
enlighten how individuals can apply this force to themselves (Blazevich, 2012).
Newton’s Third Law
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| (Law, 2010) |
For every action, there is an equal
and opposite reaction.
When
an individual is in contact with the ground a vertical force is applied
downward through the base of the foot. At the same time the ground will exert
an equal and opposite vertical force upwards, this is known as ground reaction
force (GRF). In the jumping motion an individual will apply a force with both
vertical and horizontal components. The ground will then exert an equal and
opposite GRF which will accelerate the individual forwards and upwards as long
as the force exerted is larger enough to overcome their inertia. To ensure that
the force is large enough to overcome their inertia an individual must apply
the greatest possible force against the ground while at the same time ensuring
that this force is directed in a very specific and opposite direction to which
they wish to travel (Blazevich, 2012). The last component which needs to be
explored in order to optimise jump height is Newton’s law of gravitation.
Newton’s Law of Gravitation
All bodies are attracted to each
other with a force proportional to the product of the two masses and inversely
proportional to the square of the distance between them:
As
explained in Newton’s second law a smaller individual in relation to mass can
accelerate their body greater under a given force. When jumping an individual
is moving vertically and is affected by gravity. The law of gravitation
outlines that if the product of two masses is lighter, the influence of gravity
is then smaller. One of the two masses is the Earth, which means in order for
the influence of gravity to be lessened an individual must reduce the mass of
their body (Blazevich, 2012).
The
law of gravitation allows for the calculation of gravitational force, total
force of an individual or object and the acceleration of an individual or
object. Let’s compare the results of these values for our two basketball
players.
By
being lighter Nate ends up with a greater net force which allows him to
accelerate upwards at a much higher speed. An objects inertia is proportional to
its mass, so since Yao is much heavier he requires a larger force to accelerate
which is then amplified because of the effects of gravity when both players are
moving vertically.
The
above information allows us to determine that in order to maximise jumping
height we need to manipulate a number of factors. The first being the need to
overcome our inertia (Newton’s First Law) which is achieved by having a force
applied against us (Newton’s Second Law). This is accomplished by applying a
large and well directed force against the Earth which in turn will apply an
equal and opposite reaction force against us (Newton’s Third Law). The sum of
the forces determines one’s acceleration and the force of gravity acts
downwards (Newton’s Law of Gravitation), therefore in order to achieve a maximum
jump height large vertical forces or having a lower body mass is required.
Is it possible for an athlete to
manipulate their body position whilst jumping in order to achieve a maximal
jump height?
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| (McGinnis, 2013) |
When
an athlete jumps they apply a force to the ground to accelerate their mass
upwards. This allows their body to attain a vertical velocity, the movement of
the athletes body is represented by the movement of their centre of
mass/gravity (Blazevich, 2012). Centre of gravity is the point in an object or
individual where which its mass is evenly distributed and through which the
force of gravity acts. Centre of mass is the point within a body where the
entire mass may be assumed to be concentrated. For objects and individuals near
the Earth centre of gravity and centre of mass are equivalent terms and may be
used interchangeably. The location of the centre of mass/gravity within an individual’s
body depends on the position of their limbs. If they stand upright with their
arms to the side then the location of the centre of mass/gravity will be approximately
55-57% of their standing height within the midsagittal plane (McGinnis, 2013).
The
reason the location of the centre of mass is important is because we are able
to manipulate its location by changing the position of certain body parts which
in turn can lead to achieving higher jump results. The elemental units of the
body are the limbs, trunk, head and neck and it’s with changes to these
elements that determine changes in the centre of gravity for an individual. The
movement of each limb shifts the centre of gravity for the entire body in the
direction to which it moves, how much is relative to the weight of the limb and
the distance it moves.
There
are three common techniques for jumping which an athlete might use to try and
achieve a maximum height. These are; (1) Jumping with one arm above their head,
(2) Jumping with both arms above thier head and (3) jumping with both arms and
both legs raised. Which technique would allow for a maximal jump height, that
is which of the three ensures the greatest distances from the reaching arm to
the ground? If you tried this yourself you would find that technique 1 allowed
you to reach the highest. Assuming that the centre of gravity for each
technique reached the same heights, it is important to
maximise the vertical distance between the centre of gravity and the
outstretched arm in order to achieve maximal reach height. Techniques 2 and 3
move the centre of gravity closer to the head which essentially moves it closer
to the reaching arm. By keeping all limbs and other elemental units of the body
besides the reaching arm low it maximises the distance between the reaching
hand and centre of gravity in the body thus making technique 1 the most
effective.
The Answer
Professional
basketball players must be tall to be competitive in the NBA. However just
because one player has a distinct height advantage over another it will not guarantee
success. Teams are made up of athletes
of different sizes who have defined skills and valuing or devaluing strictly
because of their size is an antiquated exercise.
With
greater height comes longer wingspan and reach which helps in attempting to
block shots and battle for rebounds. What a basketball player gains in leverage
thanks to his height, he may lose on other aspects including speed and agility.
Shorter players tend to have less mass which thanks to Newton’s Law of
Gravitation allows them to achieve a larger maximum jump height with the use of
less force compared to their heavier and taller counterparts. This coupled with the correct jumping
technique of jumping with one hand raised to block a shot in order to maximise
the distance between their centres of gravity and blocking hand allows players
of shorter stature to out jump a taller opponent in order to rebound or block a
shot.
How else can we use this information?
Newton’s
Laws of motion are not limited only to jumping, producing forces in specific
directions is an important fundamental ideal for any sporting success. All
coaches and athletes need to consider how to optimise force production for
their desired field of expertise. Understanding how to produce forces and in
what direction these forces should be applied in order to achieve acceleration
in that desired direction is important in all sports. It is the role of coaches
to determine their player’s optimum techniques thus ensuring attainment of some
threshold level for maximum strength, power, and speed (Harris, 2000).
The
manipulation of the location of the centre of mass/gravity within an athlete’s
body is also used in many other sports. Evasive sports such as football and
rugby have players who move their arms and legs in one direction so that their
trunk can move in another to ensure that they do not get caught by an opponent.
This manipulation allows for the explanation of why some basketball players,
dancers, figure skaters and gymnasts appear to defy gravity by hanging in the
air during some of their jumps. During these jumps the head stays at the same level
but the centre of mass follows a parabolic path as the jumper’s legs and arms
rise and then fall.
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| (Blazevich, 2012) |
References
ABS. (2012). Profiles of Health, Australia.
HEIGHT AND WEIGHT. from http://www.abs.gov.au/ausstats/abs@.nsf/Lookup/4338.0main+features212011-13
Blazevich, A. J. (2012). Sports
Biomechanics the Basics Optimising Human Performance 2nd Edition. London:
A&C Black Publishers Ltd. Ch 4 & 6.
Gagen, L. & Getchell, N. (2008).
Applying Newton's Apple to Elementary Physical Education: An Interdisciplinary
Approach. Journal of Physical Education, Recreation & Dance, 79(8),
43-51.
Harris, G., Stone, M., O’brayant, H.,
Proulix, C. & Johnson, R. (2000).
Short-Term Performance Effects of High Power, High Force, or Combined
Weight-Training Methods. Journal of Strength and Conditioning Research, 14(1),
14-20.
Law, J. (2010). Epic martial arts Blog. Driving
from the feet. from http://epicmartialarts.wordpress.com/category/sports-science/
McGinnis, P. (2013). Biomechanics of
Sport and Exercise Third Edition. Champaign, IL: Human Kinetics. Ch 5.
NBA. (2007). 2007-08 Player Survey: Height.
from http://www.nba.com/news/survey_height_2007.html
RockoTR (Producer). (2006). Nate Robinson
vs Yao Ming. Retrieved from https://www.youtube.com/watch?v=fp7GcTVxXW0
Samozino, P. (2010). Jumping ability: A
theoretical integrative approach. Journal of Theoretical Biology, 264,
11-18.
