The Fitness Barometer Problem
Exploring why fitness can’t be reduced to one number or one test.
In my last piece, I wrote about how different training systems define movement in completely different ways. Strength programs are built on patterns. Mobility systems are built on joints. Locomotion models are built on gait. Conditioning is built on repeatability. Each one starts from a different idea of what matters most.
Naturally, that raises the next question: if every system defines movement differently, how do we define fitness itself?
Most people assume fitness is simple to measure. Lift more weight. Run a faster mile. Move without pain. Improve mobility. Increase your step count. Change your body composition. But each of these measures only describes a fraction of what fitness can mean.
That’s the fitness barometer problem. We have endless data points, but none of them capture the whole thing. Each one reflects a worldview more than it reflects an absolute truth.
Everyone Is Holding a Different Barometer
Ask a strength-focused person, and fitness comes down to how much force you can produce in fundamental patterns.
Ask an endurance athlete, and fitness becomes your ability to maintain output over time.
Ask someone who prioritizes mobility, and they’ll describe fitness through the lens of usable, controlled range.
Ask someone who lives in the realm of sport or athleticism, and fitness becomes about agility, rotation, and fluidity.
Ask the everyday person, and it often revolves around energy, comfort, and the absence of pain.
Each one is a barometer that tells a true story, but only one story.
Longevity training adds yet another lens. Peter Attia’s “Centenarian Decathlon” reframes fitness around the future version of yourself: Can you carry groceries? Get off the floor? Climb stairs? Maintain balance? Hold a strong grip? These are compelling indicators because they highlight the physical competencies that tend to travel with long-term health.
What’s interesting is that many of these capacities aren’t separate from traditional strength training at all. Strength often pulls them upward. But the barometer itself is built on what longevity science values: the preservation of physical abilities across decades. Again, meaningful. Again, incomplete.
And that’s what makes this subject so slippery. Every system selects the metrics that best explain its philosophy. Every barometer is shaped by the questions it chooses to ask.
The Trouble With Trying to Measure Everything
Fitness becomes confusing when we expect a single metric—or even a handful of them—to define something as multidimensional as human capability. It’s tempting to search for one number that captures everything, something neat and definitive. But the human body doesn’t work like that.
Strength, endurance, mobility, control, coordination, resilience, adaptability—they overlap, they influence one another, and they change depending on what you value. A person can be remarkably “fit” in one sense and completely unprepared in another.
Dr. Mike Israetel recently proved this by performing a tactical fitness test alongside former Navy SEALs. He performed better than many expected, and he deserves credit for stepping into the spotlight in an arena outside his specialty. But his experience highlights an important point: even someone who is exceptionally strong and well-conditioned in one domain can feel completely out of their depth in another.
And that’s the point.
It isn’t that one system is flawed, and another is correct. It’s that fitness refuses to be captured by a single test or filtered through one physical quality. The human body expresses capability through a blend of traits, and those traits matter differently depending on the context.
When someone says, “I want to be fit,” what they’re actually saying is, “I want to be fit for something.” Without that qualifier—fit for lifting, fit for running, fit for aging well, fit for parenting, fit for sport, fit for living without pain—the word becomes vague enough to mean everything and nothing at once.
The Context Problem
Two people can use the word “fitness” and be talking about entirely different things.
A runner describing fitness isn’t talking about the same experience as a powerlifter. Someone navigating chronic pain isn’t describing the same thing as someone preparing for a sport. Someone focused on aging well isn’t describing the same thing as someone focused on aesthetics.
There is overlap here, of course. Most fitness methodologies and ideologies share common ground. Strength supports longevity. Mobility supports strength. Conditioning supports almost everything. But overlap doesn’t erase the fact that each approach is built on a different definition of what fitness should prioritize.
That doesn’t make the term meaningless—it makes it contextual. And context is uncomfortable, because it resists simple, universal answers.
What counts as “fit” for one person may not matter at all for another. Yet the industry keeps trying to funnel everyone into one box, one barometer, one definition. That’s where so much confusion begins.
What a Barometer Really Represents
Barometers don’t reveal what fitness is.
They reveal what we believe fitness should be.
They’re mirrors of our values, not proofs of universal truth.
A strength barometer reflects a belief in force production and physical capacity.
A mobility barometer reflects a belief in range, control, and joint quality.
A longevity barometer reflects a belief in durability and sustained capability across decades.
A conditioning barometer reflects a belief in resilience and repeatable output.
None of them capture the whole picture.
Each one captures a slice of it.
That’s the paradox: fitness becomes clearest not through a single measurement, but through the accumulation of many partial ones—each offering a different angle on what the body can do.
The Real Question
If the industry can’t agree on one definition of fitness—and probably never will—then the question shifts. Instead of trying to crown a single barometer as the answer, maybe the value lies in understanding what each barometer reveals.
Maybe fitness isn’t something we can pin down with one test or one number.
Maybe it’s something we observe through overlapping signals, each adding depth to the way we understand our physical lives.
Strength tells one story.
Mobility tells another.
Longevity metrics add a different dimension.
Pain, comfort, capability—these shape the experience in ways numbers never fully capture.
Rather than searching for one perfect measure, it may be more useful to ask a different set of questions entirely:
What do you want fitness to give you?
What capacities matter in the life you’re living—or the life you want to live?
What abilities feel meaningful to maintain, develop, or reclaim?
The answers won’t be the same for everyone. They shouldn’t be. The body you have, the experiences you’ve lived, and the future you imagine all shape the version of fitness that makes sense for you.
The fitness barometer problem doesn’t demand a solution.
It invites an understanding.
And once you see fitness as something defined by your context—not a universal metric—the idea of becoming “fit” becomes more interesting, more personal, and far more useful.
Because when you stop trying to fit into a universal mold, you finally have the freedom to build a version of fitness that actually serves your life.