One Step Backward, Two Steps Forward: Do Prosthetic Legs Give
Athletes an Unfair Advantage?
Modern engineering of prosthetic limbs has allowed athletes with disabilities to perform at an
extremely high level. Double amputee Oscar Pistorius’s qualification in the London 2012
Olympics has raised concern about whether or not prostheses give athletes an unfair advantage
over their able-bodied competitors. With the advanced technology and materials in his below
the knee prostheses, Pistorius is able to take faster steps while running; however, Pistorius’s
need to exert more energy with each step ultimately balances his performance for fair
competition. There will inevitably be a day when prosthetic performance will surpass that of the
human body, but proper knowledge of its benefits can still preserve the fairness of sports while
allowing disabled athletes to show their full physical potential.
Introduction
Hollywood has never fallen short in creating alluring fantasies when it comes to
prostheses, with a bionic human or cyborg featured in movies such as The Six Million Dollar
Man, Robocop, and Ironman. As today’s technology continues to advance, many are left
wondering just how much longer it will be until prostheses surpass human performance.
With their birth in Egyptian, Roman, and Greek civilizations, prostheses have been
engineered for over 25 centuries. While the earliest designs demonstrated admirable
innovation using copper, iron, and wood structures with leather straps to create artificial limbs,
the progression of prostheses remained relatively stagnant for many centuries thereafter [2].
Hollywood’s depiction of pirates with peg legs and hooks for hands were somewhat accurate
for many centuries, as people often used whatever materials were readily available to create
makeshift prostheses [1]. This continued until the early 16th century when French surgeon
Ambroise Pare sparked the growth of scientific prosthetic development by introducing
amputation as an effective life saving technique [2]. Further advancement followed into the
19th century as prostheses became more secure by fitting to body sockets and allowing minimal
movement through muscle contractions. War injuries in the 20th century forced amputation
techniques to improve as they were performed strategically to fit prostheses, improving the
everyday lives of many disabled veterans [3].
This progress has increased exponentially with modern
engineering technology, incorporating lightweight materials that
are stronger and more versatile with natural movement.
Neurological prosthetic capabilities have also been introduced,
allowing users to perform impressive, dexterous tasks [1]. More
recently, prosthetic legs have received much attention due to the
Paralympic, South African athlete Oscar “Blade Runner” Pistorius
and his appearance in the London Olympic Games of 2012. As the
first Paralympic athlete to qualify to race against able-bodied
competitors, Pistorius has received both praise and criticism
for his amazing feat. While many celebrate his perseverance
to overcome his two missing fibula bones, others question
the power behind the technology in his two prosthetic legs
Figure 1
PIstorius’s two prosthetic legs have
received much criticism for giving
him an unfair, competitive advantage.
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23.1360861193!/img/httpImage/image.jpg_gen/der
ivatives/landscape_635/oscar15n-2-web.jpg
as seen in Figure 1. Despite Pistorius’s last place finish in his semi-final Olympic event, many
sports fanatics were left wondering: Do prosthetic legs give athletes an unfair advantage?
Hydraulic Knees in Trans-Femoral Prostheses
In order to evaluate the advantages and disadvantages of modern prosthetic legs, it is
first necessary to understand the different types available. Because the type of prostheses a
patient receives is dependent on the portion of the leg that is missing, there are two general
categories: an above the knee prosthesis, known as a trans-femoral prosthetic leg, or a below
the knee prosthesis, known as a trans-tibial prosthetic leg.
Individuals who wear trans-femoral prostheses face many
challenges with normal movements as they have to exert
approximately 80% more energy than individuals with two normal legs
[5]. This difficulty comes from the complex mechanics of the knee as
seen in Figure 2, and its absence severely restricts mobility for a wide
range of activities. Although trans-femoral prostheses pose a limited
risk for unfair athletic competition, the advanced engineering
behind these prosthetic legs shows impressive potential.
The components of a trans-femoral prosthetic include a
socket, knee, shank or shin, and foot-ankle as seen in Figure 3. The
Figure 2
The trans-femoral prostheses have
complex knee components that restrict
mobility
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socket is secured to the limb via customized fit and a Silesian bandage, which is simply a
circumferential elastic band, that attaches the limb or a pelvic belt that more securely attaches
the prosthesis. The knee, which is the most advanced part of the leg prosthetic, is composed of
a single-axis constant friction joint powered by a hydraulic piston that
adjusts to movement [4]. Because the knee typically faces forces that
can be double and even triple the bodyweight of an individual, it must
be constructed with strong material that is also light. In response to the
amount of stress on the knee, it also has a safety feature in its hinge
structure to not buckle backwards from excessive force, and its
hydraulics can be adjusted based on the activity performed such as
running, jumping, and walking. While the hydraulic system is very
impressive and can be adjusted to give significant power for athletic
activity, its unnatural movement is not enough to rival the natural
mechanics of a normal limb [4]. Although the shaft or shin of the
trans-femoral prostheses has no special qualities other than its light
weight, the foot-ankle can provide a notable advantage. Even
though ankle mobility may be limited with certain foot-ankle
Figure 3
The trans-femoral prostheses contain
four components from top to bottom:
the socket, knee, shank, and footankle
http://www.oandp.com/resources/patientinfo/man
uals/ak6.htm
attachments, designs such as the J shaped flexible heel can provide significant running power
from the potential energy in its spring like structure.
Spring Powered Feet in Trans-Tibial Prostheses
Trans-tibial prostheses, worn by the majority of Paralympic runners, are far simpler due
to their attachment below the knee. Because these prostheses avoid the complexities of an
artificial, load bearing joint, they may offer an athletic advantage to their users due to the
power generated in their the foot-ankle mechanism supplemented by the power of a
functioning, human knee. Similar to the trans-femoral prosthesis, the trans-tibial prosthesis
consists of a socket, suspension system, and foot [4]. The socket and suspension system of the
trans-tibial prostheses are almost exactly identical to that of the trans-femoral prostheses, with
the exception of a better fitted suction system. The suction system of a trans-tibial prosthesis
does not have to support the entire load of the upper body due to the force dispersed in the
human knee, allowing it to have a better fit to its user. As for the foot, the most commonly used
unit is the “SATCH”, also known as Solid Ankle Cushion Heel [5]. This model is used with transfemoral prostheses as well, simulating a real foot with a lightweight, inexpensive, and smooth
material. However, the trans-tibial prostheses utilize the J shaped flexible heel more efficiently
than the trans-femoral prostheses due to their
laminate and fiber reinforced plastic exoskeleton that
distributes more bodyweight into the foot
mechanism. Trans-femoral prostheses do not have
this capability due to the artificial knee joint’s
hydraulic piston absorbing some of the force that
would normally be generated into the foot [5]. The J
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pistorius_2008_getty_prostheticlimbs.jpg
shaped flexible heel is the most criticized component
of the trans-tibial prosthesis as many believe that its spring like quality helps runners move
faster with less effort.
Unequal Footing in the Olympics?
Oscar Pistorius’s two trans-tibial prostheses have been criticized as an unfair advantage by both
sports fans and scientists alike. In 2007 a research experiment conducted by Wolfgang Potthast and
Gert-Peter Brueggemann for the International Association of Athletics Federations (IAAF) ruled that the
double prosthetic biomechanics allowed Pistorius to increase his stamina unnaturally. Potthast and
Brueg found that Pistorius experienced lesser deceleration rate on each step due to the force absorbed
by his flexible heel reducing the force on his knee, allowing him to make each subsequent step faster
than his able bodied counterparts [6]. Thus, Pistorius was not allowed to compete in the Bejing Olympic
Games in 2008 despite his qualifying time.
However, what the study for the IAAF failed to recognize was that Pistorius’s legs had to exert
more energy with each step despite his faster limb movement. Another set of experiments performed
by Hugh Herr before the London Olympic Games in 2012 revealed that Pistorius consumed the same
rate of energy and oxygen as a normal competitor, and Pistorius experienced normal signs of fatigue.
Herr also argued that the same technology for prostheses has been around for several years, yet no
athlete was able to perform at the same level as Pistorius [7]. It soon became apparent that although
the Bladerunner’s carbon fiber legs showcased advanced technology, they did not enhance his
performance as an athlete. The IAAF ruled that Pistorius’s prostheses did not provide any unfair
advantage and restored his much deserved athletic reputation [7]. Although Pistorius continued on to
finish last in his semi final event, his participation in the Olympics was a historical step forward for
biotechnology.
The Olympics have long been regarded as a test of the physical and biological capabilities of the
human body, which still holds true in Pistorius’s case. Born without fibulas in either leg, the Bladerunner
was capable of competing with his prostheses at the highest level while still maintaining fairness in the
sport. If anything, this should encourage engineers to explore the prosthetic technology even further to
ascertain what should and should not be allowed to be used in athletic competition. There will inevitably
be a day when prosthetic performance will surpass that of the human body, but proper knowledge of its
benefits can still preserve the fairness of sports while allowing disabled athletes to show their full
physical potential.
Stepping Forward
Prosthetic legs are only one example of the many different prostheses currently being
developed. Artificial eyes, ears, organs, and hands are researched by engineers to improve the
lives of disabled individuals. This will continue to draw criticism towards prosthetic users,
judging whether or not they have been given an unfair advantage in athletic competition. Even
medical procedures such as laser eye surgery have been questioned as they may provide golfers
with superhuman sight that other competitors may not have access to. What many people fail
to realize is that sports were created to celebrate human performance and the amazing
physical feats that surpass normal expectations. This is not to say that athletes should cheat or
use performance enhancing drugs, but athletes’ grand performances from doping have still
impressed fans worldwide, for they reveal the potential of the human body. It is important to
remember to embrace advancing biotechnology along with its physical accomplishments as one
step forward for any individual is an equal step forward for the entire human race.
References
[1] I. Clement “The History of Prosthetic Limbs”, 2011, Internet: http://science.howstuff
works.com/prosthetic-limb3.htm
[2] M. Bells, “The History of Prosthetics”, 2012, Internet: http://inventors.about.com /library/
inventors/blprosthetic.htm
[3] K. Norton, “Prostheses” in inMotion Volume 17 issue 7, 2009, Available:
http://www.amputee-coalition.org/inmotion/nov_dec_07/history_prosthetics.html
[4] A. Muilenburg and B. Wilson, “The Definitive Above-Knee Prosthesis” in A Manual for
Above-Knee Amputees, 1996 http://www.oandp.com/resources/patientinfo/manuals/ak6.htm
[5] “Trans-tibial (Below-Knee) Prosthesis” in Ballert Orthopedic of Chicago, http://www.ballertop.com/pdf/BKInstructionSheet.pdf
[6] W. Potthast and G. Brueggemann, “Comparison of Sprinting Mechancis of the Double
Amputee Oscar Pistorius with Able Bodied Athletes” in International Conference on
Biomechanics in Sports, 2010 https://ojs.ub.uni-konstanz.de/cpa/article/view/4601/4288
[7] N. Wolchover, “Oscar Pistorius Prosthetics Unfair? Some Say ‘Blades’ Give Runner Edge, But
What Does Science Say?”, 2012, Internet: http://www.huffingtonpost.com/2012
/07/26/prosthetic-limbs-unfair-advantage-oscar-pistorius_n_1706146.html