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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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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

slide12

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
slide18

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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