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Below are extracts from a very extensive article regarding Oscar Pistorius.
This topic was discussed quite recently on the list. Members may like to
add additional comments to the below:
Wednesday, July 11, 2007
Oscar Pistorius - Science and Engineering vs Training. The first and
only evaluation of ALL the evidence
_http://scienceofspohttp://scienhttp_ (http://scienceofsport.blogspot.com/)
So over the last month or so, we've had quite a big response to some
articles written about Paralympic sprinter Oscar Pistorius. He is
bidding to be allowed to run in the Beijing Olympics in 2008 for able-
bodied athletes. We've carried a series of articles looking at the
scientific merits of the case - there is a possibility that the
Cheetah prosthetic limb gives him an advantage, and we wanted to look
at the possible basis for this.....
The following four key issues are what I would consider important to
the argument on Oscar Pistorius' desire to compete in the Olympic
Games in 2008. I really do believe that each is critical to the
argument and would respectfully suggest that no article is complete
without sufficiently mentioning each one.
1. Incentive clarification........
2. The role of the IAAF..........
3. Evaluation of the scientific arguments
There are perhaps three key arguments for why the limbs would provide
an advantage. What I will do is summarize each of these three
arguments below... .
Key scientific argument 1
Spring design of the legs and implications for running
Firstly, there is the issue of the design of the limbs – the limb is
specifically designed to store and then return as much energy as
possible. In fact, if you go to the Ossur website (Ossur is the
company which manufactures the limbs), you will see statements to
this end. I quote verbatim one such statement below:
"Vertical forces generated at heel contact are stored and translated
into a linear motion described as Active Tibial Progression, from the
foot-flat to toe-off phase. This action reduces the need to actively
push the body forward using the contralateral foot as well as
equalizing stride length"
This statement is effectively saying that the prosthetic limb is able
to take the forces that are generated DURING LANDING, store them and
then translate this into FORWARD movement. In effect, the limb is
able to propel the athlete forward. Now, a human limb is similar in
respect to being able to store energy. However, there are two
critical differences between the human limb and the Cheetah
Prosthesis.
1) Firstly, the human limb is unable to translate the energy into
FORWARD MOTION. The Cheetahs, I gather can do this because they have
their unique shape. A human limb cannot take a force in one direction
and convert it to another without requiring muscle contraction.
2) The human limb is not able to return energy PASSIVELY. In
otherwords, if you jump off a box and land on the floor, you do not
bounce up, and almost all the energy that might have been stored is
lost. This means that if you want to use that energy, a human limb
must ACTIVELY contract. There are many studies that have shown that
if a landing phase is followed by an active contraction, then at most
70% of the energy can be recovered. Some studies have found energy
return of only 30%, much less than the Cheetahs, and this is ACTIVE
return. The point is that this recovery of energy is ACTIVE – it
requires muscle contraction and therefore requires energy. Pistorius
does not require energy, and so the metabolic cost of running will be
lower and he has a potentially enormous advantage as a result.
The implication of this physiological reality is that the energy cost
of running may be reduced....
Key scientific argument 2
Reduced limb mass
The second factor is mass. A smaller mass is easier to accelerate.
Now an athlete's lower limb would usually weight between 5 and 8 kg.
In Pistorius' case, the limb is massively reduced by ultralight
carbon fiber blades that weigh no more than 1kg. This means that he
is saving approximately 6 kg on each leg when he runs. I would
challenge anyone to go out and run with an extra 6 kg tied to each
leg and see how far they get. The reduction in mass is thus a massive
advantage....
Now, the counter-argument to this is that Oscar does not have calf
muscles to assist with this force generation. This is of course true,
and so the scientific response is to look at just HOW MUCH DO CALF
MUSCLES ACTUALLY CONTRIBUTE TO PROPULSION DURING RUNNING? And the
answer is surprisingly little. In fact, studies have estimated that
during walking, only 6% of the total energy comes from the Achilles
tendon and calf, and during hopping, it rises to about 16%.
Therefore, for sprinting, we might assume it is between 10 and 15%.
This is a remarkably small amount, when you consider that the
reduction in mass is probably 90%. So he is losing maybe 15% of his
ability to push forward, but he also loses 90% of the weight of the
lower limb, and about 40% of the total weight of the limb.
In Pistorius' case, then, the main muscles that are working during
running are the hip flexors – these are the muscles that drive the
knee forward. These muscles are without any doubt doing less work
considering the greatly reduced mass that they are responsible for
accelerating.
Key scientific argument 3
Stride length and frequency
In the initial stages of the bid to be allowed to compete, one of the
key factors put forward by the IAAF and myself were the possibility
that the prosthetic limbs would provide a longer stride than for an
able-bodied athlete of the same height. There are two reasons why
this might be so:
1. The spring effect of the limbs, which was discussed previously. I
have already commented on this, and the fact remains that the limbs
are designed specifically to PASSIVELY return energy to the runner.
An able-bodied athlete must ACTIVELY contract the muscle to capture
and use this energy.
2. The fact that the prosthetics are designed to simulate the ability
of the runner to run on his toes...........
Scientific rebuttal 1 – the limbs are less efficient than a human limb
The claim has been made that the Cheetahs are in fact less efficient
than a normal human limb. A scientist has made the claim that the
human Achilles Tendon is able to release 240% of the energy it
stores. This claim is patently incorrect – I have quoted studies that
have shown that the Achilles tendon can only return between 30% and
75% of the energy it stores. Further, the human calf and tendon
cannot take force in one direction and convert it to another – the
prosthetic limb can do this, as I explained. Finally, and this is
also explained in detail above, the human limb does not return most
of the energy passively – it requires active muscle contraction. The
assertion then, that a human limb is more efficient is not correct.
My feeling is that these claims are made by scientists who will say
whatever is required as soon as the price is right.
Scientific rebuttal 2 – Oscar has as much lactic acid as other runners
In a recently published article in the Sunday Independent, Pistorius
made the following claim in response to issues about the metabolic
cost of running:
Obviously I don't have a build-up of lactic acid in the legs, but I
have the same ratio of blood per muscles in my body as everyone else,
and the only way you'd get less lactic acid would be if that ratio
was less. The IAAF haven't spoken to me and they haven't spoken to my
physios, who work on my back every day because it's screwed up with
so much lactic acid in it. I have to ice my back every day so I can
train the next day because of the lactic acid build-up.
Firstly, it must be pointed out that lactic acid is not responsible
for his back pain to begin with – lactic acid is gone from the body
within the first 30 minutes after stopping exercise, and so back pain
felt even one hour later is NOT caused by lactic acid. This is a
theory that exercise science has debunked in the last ten years, and
is thus out-dated........
Acknowledged disadvantages
At this stage, it is important to identify the single factor that is
without doubt a disadvantage to Pistorius. And here, I have no
hesitation in saying that Pistorius is at a disadvantage and that is
from the starting blocks. Because of the double amputation, and the
fact that Pistorius is running on legs that have a very small contact
area with the ground, his balance from the blocks is compromised. It
is for this reason that he starts so slowly and then has to catch up
distance on his rivals. However, in the 400 m event this disadvantage
is greatly reduced, and is almost minimized, and that is the reason
why I suggested in an interview after the 2004 Athens Paralympics
that he should consider stepping up to the 400 m event. I'm sure that
this was the plan anyway, but it made sense, because the start in the
100 m and 200 m events are so crucial. In the 400 m event, this is
less important and the result is that his disadvantage is reduced. I
dare say that the 800 m event is even more likely to be a strong one,
particularly since the metabolic theory seems so obviously correct –
no peripheral metabolites regulating performance will result in a
massive advantage, perhaps even greater than in the 400 m – you read
it here first!
So an objective analysis of the situation tells us that he has this
disadvantage, which is partially offset by the fact that he is now
running in the longer 400 m event
4. The implications of technology in athletics – the role of the IAAF
I think that it is critical for people to realise that the IAAF, as
custodian of the sport, must make a decision that stands up to
scrutiny in ten years' time. Therefore, it must be emphasized that
this is not an issue about IAAF vs Pistorius, or about Tucker vs
Pistorius. At the heart of the issue is the introduction of
technology to the sport, and the future consequences of this
decision. I would appeal to everyone to try to consider the situation
from the perspective of the IAAF. It is not a question of fear or
embarrassment that a Paralympic athlete can compete with the able-
bodied athletes. They are not "scared" of the reality. Their concern
is how their decision now will impact on the future of the sport,
regarding technology.
And the key here is that technology makes it very difficult to
regulate how improvements in sport are achieved. This is analogous to
the situation in F1, where advances in technology made cars faster
and faster, until the point was reached where driver skill was
becoming increasingly minor to the performance of a car. Now, in
athletics, we may be faced with a situation where a 0.5 second
improvement can be achieved through the slight manipulation of
equipment, and this is not acceptable, since it means that training
is difficult to quantify......
"To give me a sense of how they feel, Ossur's engineers bolt a pair
of Cheetahs to the back of two rigid plastic and leather motorcycle
boots. I clamp in and trot across the room a few times. The Cheetahs
seem to bounce of their own accord [emphasis added]. It's impossible
to stand still on them, and difficult to move slowly. Once they get
going, Cheetahs are extremely difficult to control"
Does this sound like a passive device? Do human limbs bounce of their
accord? Does it sound to you as though these Cheetahs do not play an
active role in assisting bounce and movement? And of course, the big
challenge is to control them. That's not easy, and that's what
Pistorius does best. But then he learned to walk on them, it's not
that unusual. Gymnasts are able to balance on a 5cm wide beam because
they practice for hours a day. I could not imagine being able to do
that either. But it's possible. And it's possible that in five year's
time, if the IAAF let this through, that a 26-year old American
sprinter will run the 400 m event in 39.5 seconds, because
the "shoes" he wears make it "difficult to move slowly" and "bounce
of their own accord".
====================
Jamie Carruthers
Wakefield, UK
This topic was discussed quite recently on the list. Members may like to
add additional comments to the below:
Wednesday, July 11, 2007
Oscar Pistorius - Science and Engineering vs Training. The first and
only evaluation of ALL the evidence
_http://scienceofspohttp://scienhttp_ (http://scienceofsport.blogspot.com/)
So over the last month or so, we've had quite a big response to some
articles written about Paralympic sprinter Oscar Pistorius. He is
bidding to be allowed to run in the Beijing Olympics in 2008 for able-
bodied athletes. We've carried a series of articles looking at the
scientific merits of the case - there is a possibility that the
Cheetah prosthetic limb gives him an advantage, and we wanted to look
at the possible basis for this.....
The following four key issues are what I would consider important to
the argument on Oscar Pistorius' desire to compete in the Olympic
Games in 2008. I really do believe that each is critical to the
argument and would respectfully suggest that no article is complete
without sufficiently mentioning each one.
1. Incentive clarification........
2. The role of the IAAF..........
3. Evaluation of the scientific arguments
There are perhaps three key arguments for why the limbs would provide
an advantage. What I will do is summarize each of these three
arguments below... .
Key scientific argument 1
Spring design of the legs and implications for running
Firstly, there is the issue of the design of the limbs – the limb is
specifically designed to store and then return as much energy as
possible. In fact, if you go to the Ossur website (Ossur is the
company which manufactures the limbs), you will see statements to
this end. I quote verbatim one such statement below:
"Vertical forces generated at heel contact are stored and translated
into a linear motion described as Active Tibial Progression, from the
foot-flat to toe-off phase. This action reduces the need to actively
push the body forward using the contralateral foot as well as
equalizing stride length"
This statement is effectively saying that the prosthetic limb is able
to take the forces that are generated DURING LANDING, store them and
then translate this into FORWARD movement. In effect, the limb is
able to propel the athlete forward. Now, a human limb is similar in
respect to being able to store energy. However, there are two
critical differences between the human limb and the Cheetah
Prosthesis.
1) Firstly, the human limb is unable to translate the energy into
FORWARD MOTION. The Cheetahs, I gather can do this because they have
their unique shape. A human limb cannot take a force in one direction
and convert it to another without requiring muscle contraction.
2) The human limb is not able to return energy PASSIVELY. In
otherwords, if you jump off a box and land on the floor, you do not
bounce up, and almost all the energy that might have been stored is
lost. This means that if you want to use that energy, a human limb
must ACTIVELY contract. There are many studies that have shown that
if a landing phase is followed by an active contraction, then at most
70% of the energy can be recovered. Some studies have found energy
return of only 30%, much less than the Cheetahs, and this is ACTIVE
return. The point is that this recovery of energy is ACTIVE – it
requires muscle contraction and therefore requires energy. Pistorius
does not require energy, and so the metabolic cost of running will be
lower and he has a potentially enormous advantage as a result.
The implication of this physiological reality is that the energy cost
of running may be reduced....
Key scientific argument 2
Reduced limb mass
The second factor is mass. A smaller mass is easier to accelerate.
Now an athlete's lower limb would usually weight between 5 and 8 kg.
In Pistorius' case, the limb is massively reduced by ultralight
carbon fiber blades that weigh no more than 1kg. This means that he
is saving approximately 6 kg on each leg when he runs. I would
challenge anyone to go out and run with an extra 6 kg tied to each
leg and see how far they get. The reduction in mass is thus a massive
advantage....
Now, the counter-argument to this is that Oscar does not have calf
muscles to assist with this force generation. This is of course true,
and so the scientific response is to look at just HOW MUCH DO CALF
MUSCLES ACTUALLY CONTRIBUTE TO PROPULSION DURING RUNNING? And the
answer is surprisingly little. In fact, studies have estimated that
during walking, only 6% of the total energy comes from the Achilles
tendon and calf, and during hopping, it rises to about 16%.
Therefore, for sprinting, we might assume it is between 10 and 15%.
This is a remarkably small amount, when you consider that the
reduction in mass is probably 90%. So he is losing maybe 15% of his
ability to push forward, but he also loses 90% of the weight of the
lower limb, and about 40% of the total weight of the limb.
In Pistorius' case, then, the main muscles that are working during
running are the hip flexors – these are the muscles that drive the
knee forward. These muscles are without any doubt doing less work
considering the greatly reduced mass that they are responsible for
accelerating.
Key scientific argument 3
Stride length and frequency
In the initial stages of the bid to be allowed to compete, one of the
key factors put forward by the IAAF and myself were the possibility
that the prosthetic limbs would provide a longer stride than for an
able-bodied athlete of the same height. There are two reasons why
this might be so:
1. The spring effect of the limbs, which was discussed previously. I
have already commented on this, and the fact remains that the limbs
are designed specifically to PASSIVELY return energy to the runner.
An able-bodied athlete must ACTIVELY contract the muscle to capture
and use this energy.
2. The fact that the prosthetics are designed to simulate the ability
of the runner to run on his toes...........
Scientific rebuttal 1 – the limbs are less efficient than a human limb
The claim has been made that the Cheetahs are in fact less efficient
than a normal human limb. A scientist has made the claim that the
human Achilles Tendon is able to release 240% of the energy it
stores. This claim is patently incorrect – I have quoted studies that
have shown that the Achilles tendon can only return between 30% and
75% of the energy it stores. Further, the human calf and tendon
cannot take force in one direction and convert it to another – the
prosthetic limb can do this, as I explained. Finally, and this is
also explained in detail above, the human limb does not return most
of the energy passively – it requires active muscle contraction. The
assertion then, that a human limb is more efficient is not correct.
My feeling is that these claims are made by scientists who will say
whatever is required as soon as the price is right.
Scientific rebuttal 2 – Oscar has as much lactic acid as other runners
In a recently published article in the Sunday Independent, Pistorius
made the following claim in response to issues about the metabolic
cost of running:
Obviously I don't have a build-up of lactic acid in the legs, but I
have the same ratio of blood per muscles in my body as everyone else,
and the only way you'd get less lactic acid would be if that ratio
was less. The IAAF haven't spoken to me and they haven't spoken to my
physios, who work on my back every day because it's screwed up with
so much lactic acid in it. I have to ice my back every day so I can
train the next day because of the lactic acid build-up.
Firstly, it must be pointed out that lactic acid is not responsible
for his back pain to begin with – lactic acid is gone from the body
within the first 30 minutes after stopping exercise, and so back pain
felt even one hour later is NOT caused by lactic acid. This is a
theory that exercise science has debunked in the last ten years, and
is thus out-dated........
Acknowledged disadvantages
At this stage, it is important to identify the single factor that is
without doubt a disadvantage to Pistorius. And here, I have no
hesitation in saying that Pistorius is at a disadvantage and that is
from the starting blocks. Because of the double amputation, and the
fact that Pistorius is running on legs that have a very small contact
area with the ground, his balance from the blocks is compromised. It
is for this reason that he starts so slowly and then has to catch up
distance on his rivals. However, in the 400 m event this disadvantage
is greatly reduced, and is almost minimized, and that is the reason
why I suggested in an interview after the 2004 Athens Paralympics
that he should consider stepping up to the 400 m event. I'm sure that
this was the plan anyway, but it made sense, because the start in the
100 m and 200 m events are so crucial. In the 400 m event, this is
less important and the result is that his disadvantage is reduced. I
dare say that the 800 m event is even more likely to be a strong one,
particularly since the metabolic theory seems so obviously correct –
no peripheral metabolites regulating performance will result in a
massive advantage, perhaps even greater than in the 400 m – you read
it here first!
So an objective analysis of the situation tells us that he has this
disadvantage, which is partially offset by the fact that he is now
running in the longer 400 m event
4. The implications of technology in athletics – the role of the IAAF
I think that it is critical for people to realise that the IAAF, as
custodian of the sport, must make a decision that stands up to
scrutiny in ten years' time. Therefore, it must be emphasized that
this is not an issue about IAAF vs Pistorius, or about Tucker vs
Pistorius. At the heart of the issue is the introduction of
technology to the sport, and the future consequences of this
decision. I would appeal to everyone to try to consider the situation
from the perspective of the IAAF. It is not a question of fear or
embarrassment that a Paralympic athlete can compete with the able-
bodied athletes. They are not "scared" of the reality. Their concern
is how their decision now will impact on the future of the sport,
regarding technology.
And the key here is that technology makes it very difficult to
regulate how improvements in sport are achieved. This is analogous to
the situation in F1, where advances in technology made cars faster
and faster, until the point was reached where driver skill was
becoming increasingly minor to the performance of a car. Now, in
athletics, we may be faced with a situation where a 0.5 second
improvement can be achieved through the slight manipulation of
equipment, and this is not acceptable, since it means that training
is difficult to quantify......
"To give me a sense of how they feel, Ossur's engineers bolt a pair
of Cheetahs to the back of two rigid plastic and leather motorcycle
boots. I clamp in and trot across the room a few times. The Cheetahs
seem to bounce of their own accord [emphasis added]. It's impossible
to stand still on them, and difficult to move slowly. Once they get
going, Cheetahs are extremely difficult to control"
Does this sound like a passive device? Do human limbs bounce of their
accord? Does it sound to you as though these Cheetahs do not play an
active role in assisting bounce and movement? And of course, the big
challenge is to control them. That's not easy, and that's what
Pistorius does best. But then he learned to walk on them, it's not
that unusual. Gymnasts are able to balance on a 5cm wide beam because
they practice for hours a day. I could not imagine being able to do
that either. But it's possible. And it's possible that in five year's
time, if the IAAF let this through, that a 26-year old American
sprinter will run the 400 m event in 39.5 seconds, because
the "shoes" he wears make it "difficult to move slowly" and "bounce
of their own accord".
====================
Jamie Carruthers
Wakefield, UK