The truth is that there is an incredible amount of hard science which is actively expanding our knowledge of how to best train the human body and push the limits of performance, endurance, and strength.
While it is obviously true that scientific advances at the “high end” are showing quantifiable results, it’s harder to ascertain whether the everyman/woman is benefitting, because of so many confounding factors in culture, lifestyle and such. Otherwise we would all be walking around like Greek gods/goddesses with our newfound knowledge.
It was that long ago that weight lifting was shunned by athletes because “bulking up” was thought to lower performance.
Pretty much everything in a modern gym was designed to allow more efficient or lower impact training of any particular body part or system.
If what you’re saying is that we haven’t found a magic pill to bypass the physics of metabolism and muscle growth, certainly this is true. But there’s a lot more out there than just trying to find fancy new packaging, marketing, or gimmicks to sell to people.
Even if there were no improvements at all we would expect this for no other reason than the statistics of an increasing population of athletes and our effort to pick out only the far right tail of the distribution.
Having said that, nutrition is just better now, for almost everyone, compared to the ancient Greeks. So you would also expect more athletes to come out of today's society than you would back then.
the innovation is in pharmaceuticals.
Basically I'm saying you can get all the exercise you need for general health given a landscape with varied terrain and some imagination; or a barbell, weights, and cage (which will cost <$1000 and last for 20 years); or with other basic tools like gymnastics rings. We don't need fitness fads---but people like them for various reasons. And that's fine.
The 'Algernon Argument' says simple smart drugs won't work, because we already evolved brains optimized for using the substances available to us efficiently. In the same vein, it'd be bizarre if we developed bodies that work ok for a hunter-gatherer lifestyle, but respond fantastically well to using a Bowflex for 15 minutes a day.
So if modernity is going to give us exercise benefits, it's probably going to be from changing our options or preferences around the stuff that's always worked. (And we know this is true for other animals; domesticated horses can do any one task better than a wild horse, but they lose on adaptability and resilience.) Good childhood nutrition and disease avoidance make us fitter, readily available protein probably helps too. Knee braces might help avoid cumulative damage over our longer lifespans. Since most of us don't want to exercise 5+ hours each day, things like cycling and swimming might be more efficient exercise than walking. And of course professional athletes simply pursue different goals, with consequently different tactics.
But if something comes around claiming to be better for our general health than spending a lot of time doing varied, progressive exercises, it's time to be suspicious.
Balanced exercise, progressive overload, consistency, a good diet, and enough rest are by far the most important factors in fitness. That's been the case for 10,000 years at least. Access to a barbell and bumper plates, or a bike, or protein powder makes at least an order of magnitude less difference.
Perhaps harvesting and storing honey in limited quantities as well?
George's Hebert, a French naval officer who introduced to the world the modern military obstacle course was inspired by fitness of indigenous tribes he had met in Africa.
"Their bodies were splendid, flexible, nimble, skillful, enduring, and resistant but yet they had no other tutor in gymnastics but their lives in nature."
Hebert's Grandson, David Belle, founded Parkour.