A biomechanical perspective on prostheses in athletics

Written by Mark D. Geil, Ph.D.

Oscar Pistorius garnered worldwide attention in London when he represented South Africa in the Olympic Games following years of debate over the potential benefits of prostheses for athletes. He became the embodiment of the claim that artificial legs do not offer an unfair advantage over anatomical legs. It is ironic, then, that Pistorius is arousing similar widespread attention for remarks following his historic defeat in the London Paralympics, remarks that suggested some prostheses offer an unfair advantage over others.

His comments, immediately following his loss in the 200 m final, spoke to the length of winner Alan Fonteles Oliveira’s prosthetic limbs. “We are not running a fair race here,” Pistorius said. “I can’t compete with Alan’s stride length.”

From a biomechanical perspective, there are several points to consider in this new debate, some basic and some far more complex. First, the basics. An individual with bilateral lower limb loss has the unique ability to choose his or her own height. By lengthening both prostheses, the individual becomes taller. Longer legs mean longer steps, and herein lies Pistorius’s grievance. He is suggesting that Oliviera has lengthened his prostheses, meaning he covers more ground per step during the race.

The International Paralympic Committee has recognized this possibility and has established limits to prevent prostheses that would be disproportionately long. Oliviera’s were in compliance. Apparently Pistorius believes these limits are too lax, but it’s unclear whether his complaint is with the rules as they stand today or with something he thinks Oliviera did.

The more complicated question is this: do longer strides make faster runners? The short answer is, “maybe”. Much has been made of Usain Bolt’s height, and the fact that he completes his races with fewer steps. Bolt never has looked like the prototypical runner, and his astonishing success has caused many to rethink that prototype. Nonetheless, there is far more to running than step length. Research aimed at addressing the factors that make people run fast has honed in more on the amount of time each limb is in contact with the ground, which affects step frequency. Faster limb turnover appears to be key.

For amputee sprinters, there are additional factors beyond the physiological. The stiffness of the limb affects ground contact time. The material properties affect energy return efficiency. Alignment of the limbs affects the ability to use them optimally. And, yes, their length matters too.

Pistorius’s Olympic runs established that the anatomical limb is the gold standard. His Paralympic complaint, merited or not, reminds those who govern sport for individuals with disabilities that artificial devices should remain biomimetic. And his Paralympic defeat shows that the skill level of these athletes is on the rise, the competition is becoming more intense, and we should continue to work to celebrate not disability, but ability.

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Mark D. Geil, Ph.D.
Associate Professor of Biomechanics
Georgia State University,
Atlanta, GA

Note: The views expressed in ACSM Hot Topics are those of the contributors only, and should not be construed as official statements of the American College of Sports Medicine. 

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