For elite amputee runners looking to compete side-by-side with their non-amputee counterparts, achieving parity in sport is proving to be a marathon, not a sprint.

South African runner Oscar Pistorius may come to mind: the amputee was the first to compete against non-amputee sprinters in an Olympic Games. Pistorius primarily ran the 400-meter event and placed 16th during the 2012 London Olympics using his bilateral “Flex-Foot Cheetah” prostheses developed by Össur. His success in London led to restrictions on the use of running prostheses in non-amputee events enforced by World Athletics, the international governing body of running-associated athletics. However, in 2020, this ruling was reversed by the Court of Arbitration in Sport on the grounds that it was discriminatory, unlawful, and invalid.

Pistorius running with his “Flex-Foot Cheetah” prostheses. Source: Yahoo News.

Amputees are now theoretically allowed to compete in non-amputee events, unless World Athletics can provide proof that prosthetics offer an unfair advantage. “Theoretically” because loopholes in this ruling are still used to prohibit amputees from racing.  

The fastest amputee runner today – Blake Leeper – was barred from competing in the recent 2020 (2021) Tokyo Olympics because of one of these obscurities: his prostheses made him “too tall” to participate. This rule, known as Maximum Allowable Standing Height (MASH), is mandated by the International Paralympic Committee and seeks to prevent athletes from using disproportionately long prostheses. MASH was originally established under the (false) assumption that longer legs equate to faster speeds and is not applicable to non-amputee athletes.  

Across amputees and non-amputees, Leeper’s personal best 44.42-second 400-meter currently makes him the sixth fastest man in the world in the event.

Blake Leeper competing against non-amputee athletes. Source: Runner’s World.

The race is now on to provide scientific evidence that Leeper’s and other’s prostheses are not providing any significant advantage. Dr. Alena Grabowski, head of the Applied Biomechanics Laboratory in the department of Integrative Physiology at the University of Colorado Boulder, is leading the charge to do just this.

“It’s always been the words advantage or disadvantage, well, what does that mean?” Grabowski asks. And scientifically what does that mean? Or performance-wise what does that mean?”

Bringing Leeper into the laboratory, Grabowski and colleagues measured an array of biomechanical performance metrics.

They first investigated distinct aspects of the two fastest bilateral amputees’ (i.e., Leeper and previously collected data from Pistorius) running mechanics, including: initial acceleration of the first 20 meters off the starting blocks, maximum running velocity and sprint endurance, maximum curve running velocity, and running velocity at aerobic capacity.

From the start gun, bilateral amputees appeared to be at a disadvantage. The fastest bilateral amputees generated peak horizontal ground reaction forces (i.e., the propulsive force that moves the center of mass forward) more slowly, and this peak propulsive force was around 31% lower than non-amputees. Putting it together, bilateral amputees took longer to complete the first 20 meters of the race and to reach their top speed compared to elite, and even sub-elite, non-amputees.

Amputee runners may be slower out of the blocks but can attain similar top speeds later in the race. Leeper reached max treadmill velocities of up to 11.4 meters per second (m/s), but this speed was no different, and slightly slower, than elite non-amputees (11.72 m/s) or even elite unilateral amputees (11.55 m/s). Leeper achieved this peak speed kinematically similarly to non-amputees: generating equivalent vertical ground reaction forces (i.e., the push to lift the body off the ground), stepping with similar frequencies, and moving forward comparable distances per step.  

Interestingly, the second fastest bilateral amputee, Pistorius, achieved similar peak speeds but using a different strategy of taking shorter and faster steps. The biomechanical differences between Leeper and Pistorius could likely be attributed to Pistorius’ use of stiffer prosthetics.

Running on the curves of a track (a radius of approx. 36.5 meters) tends to be slower for all runners, amputee or not. Compared to straightaway speed, non-amputee runners slowed by around 3% while Leeper slowed by around 6%. Thus, bilateral amputees appeared not to have faster curve running ability and, if anything, are 1-3% slower around the bend.

A common argument against amputee runners is that it costs them less metabolic energy to run than non-amputees because they have less muscle mass (i.e., no lower legs) to fuel via cellular respiration. Aerobic capacity, or VO2 max, is a measure of the body’s ability to extract oxygen from the blood, shunt it to the muscles, and convert it to energy. A high VO2 max means that strenuous activity can be supported for sustained periods and is often higher in endurance athletes, for example. Leeper had an aerobic capacity that was almost 45% lower than elite non-amputee runners and a speed at this aerobic capacity that was almost 14% slower.

Despite the lower aerobic capacity, Leeper proved a very economical runner. His running economy – in other words, the body’s efficiency at translating oxygen consumption into forward movement – was 19% better than non-amputee sprinters. Altogether, the parameters regarding energy expenditure while running more-or-less balanced out and provided no significant advantage to the amputees.

Second, Grabowski and colleagues performed a retrospective analysis comparing Leeper’s race performance to that of elite non-amputee sprinters that competed in the 2017 International Association of Athletics Federations (IAAF) World Championships 400-meter final.

The real-world race data echoed the laboratory findings remarkably well. The fastest bilateral amputee’s slower starts off the block and worse curve-running performance were reflected in his 8.3% slower first 100m split (which is a curve). During the second and third 100-meter splits, Leeper was 2.5% and 0.2% slower than elite non-amputees – slowly catching back up. With a final 100 meters left to kick, Leeper’s slightly improved running economy may come into play: running the final straightaway 9.9% faster than non-amputees. On the track, then, it seems as though bilateral amputee sprinters recover their slow start in the back-half of the race.

Across all measured 400-meter performance metrics, the elite bilateral amputee sprinters did not exhibit a single significant advantage (greater than 2 standard deviations) over non-amputees.

So why the intensified scrutiny of amputee runners? Distance runners, for example, are mostly free to wear Nike Vaporfly 4% shoes, which reduce the energetic cost of running by almost 4% and have been recently adopted by elite athletes everywhere. During the 2020 U.S. Olympic Trials for track and field preceding Tokyo, Nike offered a free pair of 4% shoes to any participating athlete in apparent recognition of the shoe’s discernible performance boost.

Nike Vaporfly 4% shoes. Source: New York Times.

Running shoes, however, are a choice. While there are many athletes who cannot wear Nike Vaporfly 4% shoes due to sponsorship loyalties or financial limitations (retailing at over $250.00!), athletes with amputations rely on their devices to locomote in the first place.

Leeper, and other amputee athletes seeking fairness in sport, are relying on impartial scientific biomechanics research, like Grabowski’s and others at CU Boulder, to inform the politics.

“My suggestion is to look at the athlete more than the device,” Grabowski summarized. “We focus on the device because it is different… but we need to focus on the athlete and their ability to use the device. I think that gets overlooked… How cool would it have been if we had celebrated these athletes rather than excluded them? To say – Wow! ­These folks can use this carbon fiber device in such an exceptional way – let’s think about that… And how cool would that have been for all the kids or people that have an amputation to have somebody to look up to?”

The race is not over yet for amputee runners, biomechanists, and physiologists aspiring to evolve athletics. Only when the science overtakes the engrained beliefs of sport’s governing bodies can equality of competition be achieved.

Read the science here.

By Robbie Courter

Posted by Science Buffs

A CU Boulder STEM Blog

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