Here’s a question that sounds simple but gets complicated fast: What does it actually mean to be fit?
Outside Magazine once called triathlete Mark Allen — six-time Ironman winner — the fittest man on Earth. That sounds reasonable. Until you put him next to an Olympic decathlete who matches his endurance but also beats him in strength, power, speed, and coordination. So who’s actually fitter?
Or consider a 60-year-old who shovels her own driveway, keeps up with her grandkids, and hasn’t been to a doctor with anything serious in years. Is she fit?
I’d argue yes. And I’d argue her fitness is more practical than most people who spend their lives in elite sport.
Glassman Got It Right — and Also Incomplete
In 2002, CrossFit founder Greg Glassman wrote a seminal article arguing that the fitness world had no agreed-upon definition of fitness — and without a definition, you can’t measure it, and without measurement, you can’t improve it.
His solution: define ten physical skills that together constitute fitness. Cardiovascular endurance, stamina, strength, flexibility, power, speed, coordination, agility, balance, and accuracy. A truly fit person is competent across all ten. Not elite in one. Competent in all.
He also introduced the sickness-wellness-fitness continuum: a spectrum from sick (high blood pressure, poor blood sugar, low bone density) to fit (the opposite of all those markers). Fitness, by this model, isn’t just the absence of disease — it’s a buffer against it.
This framework still holds up. Research consistently shows that people with broad physical fitness get sick less, recover faster, and maintain independence longer as they age.
But the model is two-dimensional. And fitness is actually three-dimensional.
The Missing Dimension: Fitness for What?
Tour de France cyclists have extraordinary endurance. But cycling is non-weight-bearing, and many elite cyclists have poor bone density — some comparable to people decades older. Their strength is moderate. Their fitness profile is long and narrow: extremely deep in one or two areas, shallow in others.
Are they fit? For cycling — absolutely. Perfectly adapted for their task.
Powerlifters sit at the opposite extreme. Elite strength and power, but limited aerobic capacity. Ask a competitive powerlifter to run a 5K and you’ll see the tradeoff in real time. Does that make them unfit? Not if their goal is to lift the most weight possible.
A Navy SEAL needs strength, speed, durability, and the ability to function in extreme conditions. Would more strength help? Yes. More aerobic capacity? Also yes. But at some point, adding muscle mass means requiring more calories than can be carried on a mission. Every gain in one direction costs something in another.
This is the missing dimension — the dimension of purpose. Fitness is not one number. It’s a profile. And the profile that makes you excellent at one task may make you mediocre at another.
So Who Is Actually Fit?
After nearly 30 years of coaching, here’s the answer I keep coming back to:
It depends on what you’re training for.
If you’re an athlete or your work demands physical performance, your fitness is defined by readiness. For these people, fitness is task-specific.
But most people aren’t professional athletes. Most people are trying to live well. Feel good. Do what life asks of them without being broken by it. Stay out of the hospital. Keep up with their family. Carry their groceries. Work a full day and still have energy left.
For those people, Glassman’s continuum is exactly the right framework. Push from sick toward fit across every measurable marker. Be reasonably strong, reasonably conditioned, reasonably mobile, and healthy on the inside — blood pressure, blood sugar, cholesterol, bone density. That’s the profile that protects you for decades.
The Mistake Most People Make
The most common error I see: adopting someone else’s fitness standard.
Someone sees a triathlete on social media and thinks they should be running 80 kilometres a week. Someone sees a powerlifter and thinks they need to squat twice their body weight. Someone sees a CrossFit Games athlete doing things most untrained bodies can’t safely handle.
You don’t need any of that. Chasing those standards — without a clear personal goal — can take you further from real health.
Three Things You Can Do Right Now
1. Define your fitness before you pursue it. Ask yourself: what does my body actually need to do? If you have a sport or physical job, start there. If you’re training for general health, aim to improve across all markers — strength, cardio, mobility, and lifestyle habits like sleep and nutrition.
2. Stop comparing yourself to someone else’s standard. Measure your fitness against your own goals and your own baseline. Are you stronger than six months ago? Sleeping better? Moving with less pain? Those are the metrics that matter for your life.
3. Aim for competency, not specialization. Unless you’re training for a specific competitive goal, you want a broad fitness profile. Reasonably strong. Reasonably conditioned. Reasonably mobile. Healthy inside and out. It’s not Instagram-friendly. But it works — and it keeps working for decades.
The Bottom Line
Fitness isn’t one-size-fits-all. For athletes and people with demanding physical jobs, fitness means readiness. For everyone else, fitness means moving away from sickness and toward health across every measurable marker.
Either way, the goal isn’t to look like someone on a screen. The goal is to function well, live well, and feel well — for as long as possible.
If you’re not sure what fitness looks like for your life right now, that’s exactly what we help with at Catalyst. Our OnRamp program is designed specifically for people who are new to training or coming back after time away.
The Catalyst Fitness Quickcast is a short, evidence-based podcast for busy adults who want real fitness guidance without the noise. New episodes every week at catalystgym.com/blog.
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