New data support experts' opinion that prostheses do not enhance top running speeds of amputee sprinters
Findings published today in Biology LettersNew data released by a team of experts provide further evidence that amputees using running-specific prostheses have no overall biomechanical advantages when running at top speeds compared to able-bodied sprinters. These findings were published today in Biology Letters, a journal of the Royal Society of London.
The paper's six authors are leading experts in the fields of biomechanics and physiology, and include members of the research team whose previous findings were presented to 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 Oscar Pistorius, the South African bilateral amputee who attempted to qualify for the 400-meter sprint at the Beijing Olympics. Pistorius runs using J-shaped, high-performance Cheetah Flex-Foot prostheses.
In the new study, the researchers gathered biomechanical data from six elite, unilateral amputee sprinters using running-specific prostheses. (Unilateral sprinters have one lower-leg prosthesis and one biological leg.) Data were analyzed from jogging speeds up to top sprinting speeds on a unique high-speed instrumented treadmill at the Orthopedic Specialty Hospital in Salt Lake City, Utah. The scientists compared the forces exerted on the ground and step timing from the biological leg to the leg with the prosthesis. The 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. The researchers therefore concluded that while a running-specific prosthesis can partly emulate the spring-like behavior of a biological leg, unilateral amputees cannot generate and apply as much force with their prosthesis, thus impairing top speed.
"These new data support our previous findings that passive running-specific prostheses are not able to provide the ground forces realized by biological legs, and that we are not yet at a point in time when lower-limb prostheses outperform biological limbs. But because the biomechanical and physiological comparisons of amputee runners using prostheses to non-amputee runners are so complex, we will continue conducting additional research to better understand all the factors involved," says lead author Alena Grabowski, of the MIT Media Lab's Biomechatronics group.
"Our new data clearly show a ground-force deficiency caused by running-specific prostheses," says Hugh Herr, senior author and head of the Biomechatronics group. "Unilateral amputee sprinters simply cannot strike the ground as hard and fast with their prosthetic leg as compared to their biological leg, a clear disadvantage for achieving top sprinting speeds."
The other four authors are: Craig McGowan, University of Texas at Austin, Neuromuscular Biomechanics Laboratory; William McDermott, The Orthopedic Specialty Hospital; and Matthew Beale and Rodger Kram, University of Colorado at Boulder Locomotion Laboratory. Grabowski, McGowan, Kram, and Herr were among the seven experts whose work was presented at the CAS hearing last year.
The full 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