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Running with Prosthetics: Unfair Advantage?

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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  1. Running with Prosthetics: Unfair Advantage? vs

  2. 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

  3. 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

  4. 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

  5. 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)

  6. 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

  7. “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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. “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

  15. 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

  16. 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

  17. 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

  18. 10m/s • Leg compression insert: midstance, maximum limb compression • External moment arm at knee 40% less • External moment arm at hip 65% less

  19. 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

  20. 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

  21. 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

  22. 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

  23. Who is correct? Only time can tell…

  24. 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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