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: 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 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 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 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 “Blade Runner” – Born without fibulas – J-shaped carbon fiber bilateral BK prosthetics “Cheetahs” by Ossur – Paralympic Record: s, :67s, s – 2 nd in S. African Nationals able-bodied 400m IAAF International Track Organization banned from Olympic competition Jan – 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

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

A.Contact time vs. Speed 3.5 SD higher at 10m/s B.Aerial time vs. Speed 4.4 SD lower at 10m/s C.Swing time vs. Speed 3.4 SD lower at 10m/s D.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 Running Mechanics Results

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” 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 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 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 Performance Stanced average vertical force – Lower by 0.46W b than track athletes – Fall within range of W b 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

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

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.” 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 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 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? Only time can tell…

Resources “Amputation Statistics by Cause: Limb Loss in the United States.” National Limb Loss Information Center. Revised coalition.org/fact_sheets/amp_stats_cause.pdf. 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. s/1.html s/1.html Hamilton, N. et al. “Kinesiology: Scientific Basis of Human Motion.” 11 ed McGrawHill Companies. New York, NY. O’Sullivan, S. and Sielgman, R. “National Physical Therapy Exam Review and Study Guide.” International Education Resources. Concord, MA. Weyand, P. et al. “The Fastest Runner on Artificial Legs: Different Limbs, Similar Function?” J Applied Physiology Sep;107(3): 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 Nov 19.