Should prosthetics be allowed in non-amputee events?

I wrote this just before the Olympics for PST-UK. The background to the science, specifically the legal proceedings about Pistorius, has been covered quite well before here and here.

This Is Not About Oscar Pistorius

Oscar Pistorius is an inspirational figure, a man that has achieved so much, and a human who continues to achieve and push boundaries. He is a person who I have never met, and yet have huge respect for. This is not an article about Oscar Pistorius the man. This is an article on the debate of prostheses in sport. Pistorius’ name will come up, and be used as an example. But this is only because most of the little research we have is based on him, and the main reason that this has become a debate is because of the progression he has made; he is also the only athlete that this debate is current for.

English: South African Paralympic runner Oscar...

South African Paralympic runner Oscar Pistorius (born 22 November 1986). (Photo credit: Wikipedia)

To recap (as most people will know), Pistorius was selected for the South African Olympic and Paralympic squads for London 2012. Pistorius is a double below-knee amputee athlete who competed in the 100, 200, and 400m sprints in the Paralympics, and the 400m sprint in the Olympics. He was not the first athlete to compete in both the Paralympic and Olympic games though. In 2008, Natalia Partyka (Poland) who was born without her right hand competed in Table Tennis, whilst Natalie du Toit (South Africa) who had her left leg amputated following a crash competed in swimming. Others have also competed in both competitions. However, previous athletes did so without the technological aids such as the prostheses worn by an amputee sprinter.

English: Natalia Partyka - polish disabile tab...

Natalia Partyka(Photo credit: Wikipedia)

The ability to travel at either high speeds or long durations is a requirement for nearly any sport. Travelling long distances (marathon) at high speeds (100m speed) is not an option; largely due to energy delivery options and fatigue within the body. The prosthesis is a necessity for an amputee in order for them to run. There are two main questions that need to be focused on within this debate; a) do prostheses cause a different running style and b) do prostheses provide an advantage for the lower limb amputee?

Do Prostheses Cause A Different Running Style?

“[I]n general, sprinters with running specific prostheses use different strategies than athletes with two biological legs to achieve faster speeds”  (1). This was the conclusion presented following the testing of “eight elite Paralympic sprinters (six with a unilateral transtibial amputation and two with bilateral transtibial amputations) and 12 sprinters of similar ability without amputations”  (1). This group of scientists assessed a variable known as leg stiffness of the runner. This measures how much the leg bends (compresses) due to the forces travelling through the leg whilst the foot is in contact with the ground, and it is deemed an important variable linked to running ability and performance. In biological legs, the leg gets stiffer (or stays the same) the faster we run i.e. it bends less for a given force travelling through it. However, the opposite was seen for amputee runners, with a decrease in leg stiffness being measured for an increase in speed. The finding that the change in leg stiffness with speed was in the opposite direction (i.e. it wasn’t just small differences in the change, it was affected in a completely different way) emphasises the difference in running mechanics of amputee and non-amputee runners.

Additional research supports this suggestion that amputee runners have a different running style to their biological-legged counterparts. Weyand and Bundle  (these two are big names in the science of running; (2)) presented data that suggested that the running mechanics were different for Pistorius (this was data collected for the legal hearings) than for 400m runners of an equivalent standard. Pistorius spent more time in contact with the ground and contacted the ground more often. The profile of the force that Pistorius applied to the ground was also different in terms of magnitude and timing.

So, the current set of data that we have suggests that amputee runners run differently to their biological-legged counterparts. This is pretty obvious if you are to observe a race (specifically one with both sets of athletes in). But then everyone runs slightly differently. The big question is whether these differences result in an advantage for amputee athletes who wear running specific prostheses.

Do Prostheses Provide An Advantage For The Lower Limb Amputee?

Prior to the Beijing Olympics in 2008, the initial ruling by the International Association of Athletics Federations (IAAF) was that Pistorius was not allowed to compete against able-bodied athletes in major competitions. This decision was made following the presentation of data from a group of very highly respected scientists led by Dr Brüggemann of the German Sport University Cologne, Germany (3). They undertook an extensive series of biomechanical and physiological tests on Pistorius whilst running, and compared this to able-bodied 400m athletes of a similar standard. Not only did they measure the same types of data I have presented above, but they also measured the amount of work the ankle, knee, and hip, performed in both sets of athletes.

When running, the leg compresses during landing, and then extends during the push off. During the compression of landing, we are able to store energy in the muscles and tendons of our legs. This is very similar to when you stretch an elastic band, or compress a spring. This stored energy can then be utilised during the push off, and is commonly referred to as “free energy” as it doesn’t take much effort from us to produce (it’s largely an effect of gravity pulling us down that causes this). Tendons are actually quite good at storing and releasing this energy; when we hop on the spot, the muscle doesn’t change length much, instead, it is the tendon lengthening during landing (which stores the energy) and shortening during take-off (which releases this free energy) that keeps us hopping. However, we still need to activate the muscle to hold it in a certain position to allow the tendon to do the work. Although tendons are quite good at storing and releasing this energy, the inclusion of the muscle, reduces this overall efficiency.

The work performed by Dr Brüggemann and his colleagues found that the prostheses used by Pistorius were significantly better at storing and releasing this energy. In biological-legged runners, the inability of the ankle joint to return all this energy resulted in the need of extra work from the knee and hip; something not found in Pistorius. The data collected led the authors to conclude that there was a “mechanical advantage of more than 30% when the leg is substituted through the prosthesis”  (3).

Generally, as an overall measure of how hard someone is working, sport scientists measure the air breathed in and out by an athlete whilst performing the activity. The use of oxygen by the body is primarily for energy production and so any changes in oxygen breathed in is a reflection of how hard the individual is working. The work performed by Dr Brüggemann and colleagues found that Pistorius required less oxygen whilst running at the same speeds as biological-legged athletes. This is probably due to the decreased muscle mass that an amputee athlete needs to contract, and the improved “free” energy that the prosthesis can reuse compared to the biological ankle.

As I said previously, the decision by the IAAF to not allow amputee sprinters wearing prostheses to compete against biological-legged runners used the research by Dr Brüggemann and colleagues in the original decision. However, following a challenge to this by Pistorius and his team (presented to the Court of Arbitration for Sport; CAS), more research was undertaken by a group of scientists from America  (4), which included Weyand, Bundle, and Kram (Dr Kram led on the research presented earlier showing differences in how amputee and biological-legged athletes run). Although, there is debate about how much of this data was actually presented to CAS due to legal reasons in the proceedings.
The second set of data compared Pistorius to other elite 400m sprinters (much like the original research) and agreed with the findings that Pistorius was more efficient than biological-legged 400m sprinters. However, they then included the oxygen utilisation of elite and sub-elite distant runners, and suggested these were not different to Pistorius (although Pistorius was still more efficient; just not by as much as when compared with 400m sprinters). It’s important to note here that distant runners train their whole career to be efficient, and as a result are more efficient than sprinters. So it is probably not appropriate to compare distance runners with 400m sprinters. However, the aim for this argument in the second trial was to show that Pistorius’ efficiency was in the range seen by biological-legged athletes, regardless of their event.

Bringing It Together

It is a fair conclusion that lower-limb amputee athletes running with prostheses incorporate a different running action to their biological-legged counterparts. The data also suggest that a greater amount of “free energy” is stored and released by the prosthesis as compared to a human ankle. Thus requiring the amputee athlete to produce less force from their knee and hip than a biological-legged athlete whilst running at a given speed.

The closing comments made by Dr Brüggemann’s group in their report to the IAAF pretty much sums up most of the research;

“Sprinting with the artificial limbs (Cheetah) is – from a biomechanical perspective – a “bouncing” locomotion and is significantly different to sprinting of able-bodied athletes on hard surface. It is a different kind of locomotion at lower metabolic cost.”

What Next?

It is always difficult to compare things that are different. Unfortunately, that is what is necessary for the debate of whether amputee runners should be allowed to compete in the Olympics. At the moment, the IAAF is treating Pistorius as a unique case and has not set a global ruling. If/when one is set, there needs to be criteria set in place for the prostheses allowed. However, because the running style is so different, and the energy required is different, how this is decided is completely unknown. I cannot foresee an easy answer to what should and what shouldn’t be accepted.

But for now, the IAAF removed rule 144.2.e from their rulebook following the Pistorius ruling:

Rule 144.2.e (2008)

“For the purpose of this Rule the following shall be considered assistance, and are therefore not allowed:

use of any technical device that incorporates springs, wheels or any other element that provides the user with an advantage over 
another athlete not using such a device.”

As such, amputee runners are free to run in the Olympic Games.

1. Kram R. Leg stiffness of sprinters using running-specific prostheses. J R Soc Interface 2012.

2. Weyand PG, Bundle MW. Point: Artificial limbs do make artificially fast running speeds possible. J Appl Physiol 2010;108(4):1011.

3. Brüggemann GP, Arampatzis A, Emrich F. A study performed on the request of the IAAF. Biomechanical and metabolic analysis of long sprint running of the double transtibial amputee athlete O. Pistorius using cheetah sprint prostheses – comparison with able-bodied athletes at the same level of 400m sprint performance.

4. Weyand PG, Bundle MW, McGowan CP, Grabowski A, Brown MB, Kram R, Herr H. The fastest runner on artificial legs: Different limbs, similar function? Journal of Applied Physiology 2009, Sep;107(3):903-11.

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