When horse racing fans rhapsodize about Secretariat’s enormous heart, they’re not speaking metaphorically — a postmortem exam in 1989 found that it weighed between 21 and 22 pounds, two-and-a-half times more than the average thoroughbred’s heart. The legendary horse also had a perfectly proportioned bone structure, flawless biomechanics, and a seemingly innate hunger for the finish line. 

In 1973, he not only swept the Triple Crown — the Kentucky Derby, the Preakness Stakes, and the Belmont Stakes — but also set records in all three races, winning the Belmont by 31 lengths. Those records still stand more than half a century later, and with each passing year, it seems increasingly clear that Secretariat was as good as horses get.

Whether humans, too, have reached peak performance is a question that surfaces with every Olympic Games. Are any of this year’s champions the human equivalent of Secretariat — the pinnacle of what’s possible in their chosen discipline? 

Pundits have been forecasting the imminent end of biological progress more or less since we began keeping track of sporting records. But human athletic progress may be unique. Unlike horses, we don’t just compete against each other — we vie against the clock, or the measuring tape, or grainy videos of bygone champions, armed with ever-advancing technology and an ever-expanding sense of what’s possible. Peak performance, for us, may always remain a moving target.

Biology vs. technology

There are two ways to set a world record: You can do better than anyone else, or you can make the task easier. In general, we celebrate the former and disparage the latter. 

If you train harder, eat better, improve your tactics, or master the mental game, then your performance is a triumph of biological progress — what sports bioethicist Thomas Murray calls “the virtuous perfection of natural talents.” In contrast, if you wear springier shoes, swing a lighter racket, or pull on a more buoyant swimsuit, then your apparent progress is just technological trickery. It might be within the rules, but breaking a record because you have better equipment doesn’t make you better than the previous record-holder.

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This dichotomy between biological and technological progress seems straightforward, but the boundaries between the two — where technology meets biology — are getting increasingly hazy. The hottest supplement among track athletes at the 2024 Olympics was baking soda, encapsulated in a high-tech hydrogel to enable it to be digested. At the World Athletics Championships in 2025, the hype shifted to an über-concentrated broccoli extract that alters the molecular signaling response to physical exertion. Are these virtuous nutritional boosts or nefarious technological hacks?

The most famous example of a Secretariat-like plateau in the progress of sports is running the four-minute mile, which was originally seen as a hard biological limit. After a pair of Swedes, Gunder Hägg and Arne Andersson, brought the record down to 4:01 in the 1940s, further progress seemed to stall. When Roger Bannister finally broke the barrier in 1954, he did it with the help of a technical innovation: two training partners paced him through more than three-quarters of the race, blocking the wind and setting an even tempo, before jogging to the finish. 

This dichotomy between biological and technological progress seems straightforward, but the boundaries between the two are getting increasingly hazy.

Pacing is common practice these days — “pace bunnies” are even provided to recreational runners at marathons. At the time, though, it was considered highly controversial and contrary to the spirit of sport — in 1953, track and field officials had disallowed one of Bannister’s record attempts because of illegal pacing.

The current record for running a mile is 3:43.13, a mark set by Moroccan star Hicham El Guerrouj in 1999. That’s a much longer plateau than the nine years before Bannister’s barrier-breaking run, and for most of that time, no one came close to breaking the record. But in 2023, Jakob Ingebrigtsen of Norway and Yared Nuguse of the United States both ran 3:43, narrowly missing it. If one of them breaks El Guerrouj’s mark in the next few years, cynics will no doubt credit recent innovations like baking soda, high-tech running shoes, and automated pacing lights, all of which help milers run faster.

The supershoe era

Shoes, in particular, have become a flashpoint in debates about what role technology should play in sport. In 2016, Nike produced a new type of running shoe featuring a curved carbon-fiber plate embedded in a thick midsole made of ultralight, bouncy foam. Runners wearing prototypes of the new supershoe won the men’s and women’s marathons at the Olympics that year. The shoes went on sale to the public the following year; the first model was called the Vaporfly 4%, named for the shoe’s improvement in running efficiency as determined by external testing at the University of Colorado. In the years since, supershoes have helped runners annihilate countless national and world records.

To some observers, records set in these shoes — even personal ones — are cheap and unworthy of praise. “Who’d want to produce a time that you know you don’t deserve, that is simply not genuine?” asked television commentator Tim Hutchings. “What’s the point?” But it’s not clear why this particular advance in shoes is different from previous innovations. Even Bannister had a bespoke pair of shoes with unusually thin leather to make them lighter, and he used a grindstone to make the spikes on the bottom thinner. Is El Guerrouj’s record also “not genuine” because it was set in modern spikes on a rubberized track instead of the loose cinders Bannister had to contend with?

And there’s another wrinkle to the shoe debate. The first supershoes for road running went on sale in 2017; superspikes for track racing appeared in 2019. Each innovation was followed by a surge of fast times, which is easy to understand. What’s more surprising is that overall times have continued to get faster each year since then. While the causes aren’t clear, one theory is that supershoes’ thick, bouncy midsoles have permitted runners to train harder without getting injured. In other words, it’s not just that technology is making people instantly and effortlessly faster; it’s enabling people to gradually alter their biology through the painstaking process of harder training.

There’s a similar tension in debates about the use of brain-enhancing technology. Studies conducted over the past decade suggest that a technique called transcranial direct-current stimulation (tDCS) might boost strength, endurance, and cognitive performance. During tDCS, a mild electric current is delivered through electrodes on the scalp to enhance communication between different regions of the brain. While some bioethicists believe tDCS is a clear example of technology altering performance from the outside, others argue that it doesn’t enhance performance — it simply helps unlock capabilities that are already present in the body.

The spirit of sport

These are the esoteric debates lurking beneath the surface when we ask whether human performance has reached its limits: The answer always depends on how we define the rules. 

In theory, we might say that biological progress is allowed, but technological progress doesn’t count. In practice, the distinction is too blurry to be meaningful. The World Anti-Doping Agency bans or permits drugs based not only on their safety and performance-boosting powers, but also on whether they violate the “spirit of sport.” This is essentially the same hazy concept we’re appealing to when we judge that, say, editing your genes to produce more oxygen-ferrying red blood cells would be unacceptable, but sleeping in a low-oxygen altitude tent to enhance your natural production of red blood cells is okay.

The rules we choose for athletes should be more NASCAR than Formula 1: We want the best driver to win, not the best engineering team.

Just because the border between biology and technology is blurry doesn’t mean sports governing bodies shouldn’t try to identify and enforce boundaries. Some new approaches will be permitted; others will be banned. Even an arbitrary line is better than no line at all. “One might contend that baseball would be a better game if four strikes were allowed instead of three,” the moral philosopher John Rawls once wrote in a treatise about rules. But for the game to proceed, it’s more important that everyone agrees to play with the same number of strikes than to get bogged down in interminable arguments about the optimal number.

In general, the rules we choose for athletes should be more NASCAR than Formula 1: We want the best driver to win, not the best engineering team. But it’s important not to romanticize the past too much. There was never a time when sports were a pure measure of human performance, untainted by technological aid. Roger Bannister’s pacers, the switch from cinder tracks to rubberized all-weather surfaces, vaulting poles made of fiberglass instead of bamboo — these and countless other innovations have helped keep world-record graphs sloping upward in the past, just as, say, the firehose of physiological and biomechanical data offered by wearable — or perhaps even implantable — technology will keep them sloping upward in the future.

Racing against history

Secretariat’s Triple Crown records, meanwhile, will celebrate their 53rd anniversary this year. What’s most intriguing about the records is that, in the context of horse racing, their longevity isn’t entirely unexpected. In 2006, a veterinary physiologist named David Gardner analyzed the progression of thoroughbred racing times at notable races in England, France, Australia, and the U.S. starting in the mid-19th century. Horses got steadily faster until the 1950s, at which point times began to plateau. Secretariat may be an outlier, but on average, today’s thoroughbreds aren’t measurably faster than those from the 1950s.

Human athletes, in contrast, are way faster, stronger, and more skilled than they were in the 1950s. Average times at major marathons, such as the Olympics, have dropped by more than 15% since then. This isn’t just a consequence of optimized biology or of enhanced technology. If it were, horses would have made the same progress — there’s plenty of money to be made in thoroughbred racing, and plenty of experts trying to use the latest advances in physiology, nutrition, and training to gain an edge. (Baking soda, the big new booster in human racing, showed up in horse racing in the 1980s, but has since been banned.) 

Horses can only race each other in the moment. They can’t race against the clock or measure themselves against past champions — against the ghost of Secretariat — the way humans can. The fundamental limits of progress for humans, in other words, aren’t physiological or technological — they’re psychological.

This distinctively human form of progress is what makes the Olympics so compelling — and what makes the notion of “ultimate human limits” so elusive. Whatever mark one athlete achieves, every other athlete immediately understands that this mark is now possible. Whether it takes a year, a decade, or a generation, someone will eventually get there — and then maybe a little farther. Biology and technology, meanwhile, will continue to evolve. We won’t always know which factors made the difference when a new record is set, but the trend is ever upward — and regardless of what the ad slogans say, it’s never just about the shoes.

This article is part of Big Think’s monthly issue Biology’s New Era.