Running with prosthetics unfair advantage
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Running with Prosthetics: Unfair Advantage?. vs. Purpose. Compare running mechanics in bilateral transtibial amputees using modern prosthetics to intact runners to discover any significant advantage. Interpret the findings of 3 studies:

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Running with Prosthetics: Unfair Advantage?

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Running with prosthetics unfair advantage

Running with Prosthetics: Unfair Advantage?

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Purpose

Purpose

  • Compare running mechanics in bilateral transtibial amputees using modern prosthetics to intact runners to discover any significant advantage.

    • Interpret the findings of 3 studies:

      • Point: “Artificial Limbs Do Make Artificially Fast Running Speeds Possible.”

      • Counterpoint: “Artificial Limbs Do Not Make Artificially Fast Running Speeds Possible.”

      • “The Fastest Runner on Artificial Legs: Different Limbs, Similar Function?”

        • Point/counterpoint argument features same authors


Amputation statistics

Amputation Statistics

  • 1.7 million amputees in America

    • 1/200 people

    • 3,000 people become amputees each week

  • 82% due to vascular disease

    • Of remaining 18% dysvascular, 97%= lower limb

  • Approximately 50% of lower limb amputations are transtibial

  • Prosthetic leg market grows 4% each year

    • Ossur and Otto Bock


Prosthetics terminology

Prosthetics Terminology

  • Residual limb- what’s left of limb after amputation, “stump”

  • Transfemoral/AK- above knee amputation

    • 35-60% femur spared

  • Knee disarticulation- amputation at the knee joint with femur still intact

  • Transtibial/BK- below knee amputation

    • 20-50% of tibia spared

  • Socket: connects prosthesis to residual limb, transfers forces


Running terminology

Running Terminology

  • Swing time- measured time (s) between the push-off and initial foot strike of the same leg

  • Stride time- measured time (s) between initial foot strike of the same leg

  • Leg length- measured (m) from the axis of rotation of hip joint to the ground at the outside of the heel or prosthetic blade

  • Run speed - depends on stride length and rate

  • Distance body moves per toe-off

    • Depends on takeoff angle - amt of forward lean of body over takeoff foot)


Case study oscar pistorius

Case Study: Oscar Pistorius

  • “Blade Runner”

    • Born without fibulas

    • J-shaped carbon fiber bilateral BK prosthetics

      • “Cheetahs” by Ossur

    • Paralympic Record: 100-11.17s, 200- 22:67s, 400- 47.49s

    • 2nd in S. African Nationals able-bodied 400m

  • IAAF International Track Organization banned from Olympic competition Jan. 2008

    • Prosthetics more spring than human legs

    • Appeal was approved by Court of Arbitration for Sport in May 2008

    • Did not make qualifying time of 45.95s, PR is 46.25

  • http://www.youtube.com/watch?v=ON4B-fNCvSg


The fastest runner on artificial legs different limbs similar function

“The Fastest Runner on Artificial Legs: Different Limbs, Similar Function?”

  • Published in June 2009 in the Journal of Applied Physiology

  • Question: Is running with lower-limb prostheses functionally similar to running with intact, biological limbs?

    • 3 hypotheses: metabolic cost, sprint endurance, mechanics

  • Main subject: Oscar Pistorius

  • Comparison group: past studies of elite and sub elite runners, collected data from competitive runners with similar speeds to Pistorius


1 metabolic cost of running

1) Metabolic Cost of Running

  • Hypothesis: greater than 2 standard deviations below the mean of intact groups

  • Test: interval run on treadmill

    • (Rate of Oxygen Uptake/speed of trial)

  • Result: 17% lower than able-bodied sprinters

    • 2.7 SD lower

  • Discussion: inconclusive

    • Found research of bilateral amputees having higher metabolic costs


2 sprinting endurance

2) Sprinting Endurance

  • Hypothesis: longer duration due to lightweight carbon-fiber material resisting fatigue

  • Test: constant-speed, all-out treadmill trials

  • Result: amputee sprint within same range as intact


3 running mechanics

3) Running Mechanics

  • Hypothesis: Greater than 2 SD below for:

    • Foot-ground contact times, aerial times, swing times, stance-avg vertical rxn forces

  • Test: video analysis of 2.5 m/s to 10 m/s, force software used

  • Result: Foot-ground contact 14.1% longer, aerial times 34.3% shorter, swing times 21% shorter, vertical rxn forces 22.8% less

    • All greater than 2 SD away from mean

  • Discussion:

    • vertical rxn forces less due to absence of several muscles crossing foot, ankle, and knee joints

    • Faster turnover due to weight of prosthetic and residual limb below the knee being half that of a normal limb


Running mechanics graph

Running Mechanics Graph

  • A) video images at 10.5 m/s

    • solid line shows longer contact, shorter stride, aerial, and swing duration

  • B) Vertical ground forces vs time

    • Peaks lower than able-bodied

    • Peaks arise faster

  • C) Horizontal ground forces vs time

    • More steady peak than able-bodied

    • Peaks arise faster

Black: amputee

Gray: able-body

Solid: right limb

Dotted: left limb

Weyand et. al. The Fastest Runner on Artificial Legs: Different limbs, Similar Function? J Appl Physiol 107: 903-911, 2009; doi:10.1152/japplphysiol.00174.2009


Running with prosthetics unfair advantage

Running Mechanics Results

  • Contact time vs. Speed

    • 3.5 SD higher at 10m/s

  • Aerial time vs. Speed

    • 4.4 SD lower at 10m/s

  • Swing time vs. Speed

    • 3.4 SD lower at 10m/s

  • Vertical Force vs. Speed

    • 5.2 SD lower at 10m/s

  • Comparison of Differences

    • minimal at 2.5-3m/s

    • Modest 4-5m/s

    • Pronounced 6-10m/s


Conclusion

Conclusion

  • Bilateral transtibial amputee running is physiologically similar to intact runners but mechanically not.

    • Physiological relation may be due to heavy use of extensor muscles crossing hip and knee in both groups

    • Weight of prosthetic and residual limb below knee: 2.5 kg, approximately half weight of normal limb

    • More research needed

      • Study was not in race setting: fast closing times may be due to slow acceleration b/c no ankle muscles


Point artificial limbs do make artificially fast running speeds possible

“Point: Artificial Limbs Do Make Artificially Fast Running Speeds Possible”

  • Published in Journal of Applied Physiology Nov. 19, 2009 by Peter Weyand and Matthew Bundle

  • Subjects: compare double amputee sprint runner to four track athletes and two elite male sprinters


Overview

Overview

  • Mechanical variables determine run speed

    • Quickness of reposition of limbs, forward distance while foot touching ground, force applied to ground

    • Speed=step freq*forward distance during contact*avg vertical force

  • Primary requirement to run: apply ground forces large enough to get the aerial time needed for next step

  • Average Vertical Force= total step time/contact time


Artificial limbs and performance

Artificial Limbs and Performance

  • Amputee stride frequencies

    • 15.8% greater than athletes in lab

    • 9.3% greater than elite sprinters overground

  • Short swing times=reposition limbs faster

    • 21% shorter than athletes in lab

    • 17.4% shorter than top two finishers in 1987 World Track Championships 100 m - (0.344s)

  • Contact length to leg length

    • 9.6% higher than athletes in lab

    • Due to high compliancy of artificial limb


Artificial limbs and performance1

Artificial Limbs and Performance

  • Stanced average vertical force

    • Lower by 0.46Wb than track athletes

    • Fall within range of 1.65-2.52 Wb

  • Adjusted swing times and contact lengths similar to able-body athletes

    • Speed=step freq*forward distance during contact*avg vertical force

    • speed decreased from 10.8 to 8.3m/s


Running with prosthetics unfair advantage

10m/s

  • Leg compression insert: midstance, maximum limb compression

    • External moment arm at knee 40% less

    • External moment arm at hip 65% less


Conclusion1

Conclusion

  • Two modifications that would increase bilateral transtibial amputee sprint speed:

    • Reduction in mass-> reduce swing time

    • Increase length-> increase contact time

  • Finding: Artificial limbs out perform biological


Counterpoint artificial limbs do not make artificially fast running speeds possible

Counterpoint: “Artificial Limbs Do Not Make Artificially Fast Running Speeds Possible.”

  • Published in June 2009 in the Journal of Applied Physiology by Kram, Grabowski, McGowan, Brown, and Herr

  • Question: Do modern running prostheses provide a significant advantage over biological legs

  • Overview: only one amputee tested, Oscar Pistorius- no advantage or disadvantage, give experiments needed for future


Artificial limbs vs able bodied

Artificial Limbs vs Able-bodied

  • Amputee Running Economy Higher: False

    • Worse for amputees, but did not meet p<0.05 significance

    • Only two reported bilateral transtibial: Pistorius and another runner

      • Pistorius 1.15 SD below mean, other runner 1.92 SD above mean

  • Short leg swing due to prosthetic weight: False

    • Highly neurologically trained

    • Compensates for force limitations from prosthetics

  • Amputees have lower ground reaction forces: False

    • No published GRF data for unilateral at top speed

    • Only one bilateral subject published: Pistorius

    • Pistorius was found to exert lower vertical force

      • Due to prosthetic or weak legs

      • Prosthetics must have some give and Pistorius is highly trained


Suggestion compare unilateral amputees

Suggestion: Compare Unilateral Amputees

  • Vertical force of affected to unaffected?

    • If greater vertical force with unaffected, than prosthetics are disadvantageous b/c force limitation

  • Unilateral amputees have same leg speed times between legs?

    • If true: Leg speed advantage NOT due to lightweight prosthetics

  • Adding mass will not increase leg swing or decrease time?

    • If true: weight of prosthetic is not a factor


Who is correct

Who is correct?

Only time can tell…


Resources

Resources

  • “Amputation Statistics by Cause: Limb Loss in the United States.” National Limb Loss Information Center. Revised 2008. http://www.amputee-coalition.org/fact_sheets/amp_stats_cause.pdf.

  • Epstein, D. “New Study, For Better or Worse, Puts Pistorius’ Trial in Limelight.” Inside Olympic Sports: Sports Illustrated. http://sportsillustrated.cnn.com/2009/writers/david_epstein/11/19/oscar.pistorius/1.html

  • Hamilton, N. et al. “Kinesiology: Scientific Basis of Human Motion.” 11 ed. 2008. McGrawHill Companies. New York, NY.

  • O’Sullivan, S. and Sielgman, R. “National Physical Therapy Exam Review and Study Guide.” 2009. International Education Resources. Concord, MA.

  • Weyand, P. et al. “The Fastest Runner on Artificial Legs: Different Limbs, Similar Function?” J Applied Physiology. 2009 Sep;107(3):903-11. Epub 2009 Jun 18.

  • Weyand, P. and Bundle, Kram, R. et al. “Point: Counterpoint ‘Artificial limbs do / do not make artificial running speeds possible.’” J Applied Physiology. 2009 Nov 19.


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