Experts Respond: No Scientific Evidence to Support Claim that Prostheses Offer Advantage to Amputee Runners

      

The experts presented data showing that the use of Cheetah Flex- Foot prostheses (the same prostheses worn by Pistorius) does not allow amputee sprinters to apply as much force on the ground as able-bodied runners can, thus negatively impacting an amputee sprinter's speed. In addition, they write that while Pistorius demonstrates a fast leg swing–a potential advantage because this permits a greater number of push-offs during a race–there is no scientific evidence currently available to show that this fast leg-swing speed is solely the result of the J-shaped, high-performance Cheetah Flex-Foot prostheses worn by Pistorius.

To the contrary, a study published by six of the authors earlier this month in Biology Letters, a journal of the Royal Society in England, provides additional evidence that amputee runners do not have an advantage. The scientists compared the forces exerted on the ground and step timing of six unilateral amputees (those with one prosthesis and one biological leg). Their results showed that the primary determinant of top speed–the force applied to the ground–was 9 percent less in the leg with the prosthesis. They also found that the time required for leg swing was not different between legs, and was similar to non-amputee sprinters.

"I am not aware of any scientists (other than Weyand and Bundle) who would agree there is sufficient data now available to say that Pistorius has an advantage," says Rodger Kram of the University of Colorado Boulder's Locomotion Laboratory, first author on the Counterpoint. "Weyand and Bundle provide an opinion piece that represents a radical departure from their own decade-long track record of published articles that shows that vertical ground force is the limiting factor for top speed, and that swing time is not."

"The scientific community should not make broad conclusions based on the study of one amputee sprinter," adds Hugh Herr, head of the Biomechatronics research group at the MIT Media Lab. "There could be numerous other factors involved in Pistorius' rapid leg swing, including years of training to compensate for his lack of ground force. In addition, the opinions presented by Weyand and Bundle are based upon unproven assumptions, with no new supporting data."

In addition to Kram and Herr, the Counterpoint authors are: Alena Grabowski, MIT Media Lab; Matthew Beale, the University of Colorado Boulder Locomotion Laboratory; Mary Beth Brown, Georgia Institute of Technology; William J. McDermott, The Orthopedic Specialty Hospital, Salt Lake City; and Craig McGowan, University of Texas at Austin.

They wrote their response to an opinion piece, "Artificial Limbs Do Make Artificially Fast Running Speeds Possible," by Peter Weyand of Southern Methodist University and Matthew Bundle of the University of Wyoming.

Grabowski, Herr, Kram, McGowan, Bundle, and Weyand were all members of the team whose work was presented at the Court of Arbitration for Sport (CAS) in Lausanne, Switzerland in April 2008. Those previous findings were instrumental in reversing the International Association of Athletics Federations' (IAAF) ban of Pistorius.

The "Point-Counterpoint" may be found in the Journal of Applied Physiology online at: http://jap.physiology.org/cgi/content/abstract/01238.2009v1

The Biology Letters paper, "Running-Specific Prostheses Limit Ground-Force During Sprinting" can be read at the publication's Web site: http://rsbl.royalsocietypublishing.org/content/firstcite

MIT Media Lab
Alexandra Kahn, 617-253-0365
akahn@media.mit.edu