Why CrossFit Works: The Science Behind the Methodology

Weekly Wisdom #66

CrossFit is a lot like gravity; you don’t need to believe in it in order for it to work. So, if that’s enough to satisfy you, go ahead, skip this article and just keep training.

Me, I’ve never been much of a just-drink-the-Kool-Aid guy. I want to know the why behind things.

To me, why is the most important question we should be asking, and we should be asking it often. In my experience, the best coaching conversations begin with why. I appreciate skepticism because it gives us an opportunity to question our assumptions and dive deeper into learning.

And skepticism is exactly what brought me to CrossFit.

How I Discovered CrossFit (And Tried to Prove It Wrong)

Before I stumbled upon CrossFit in 2005, I was already an experienced NCCP Level 2 judo coach attending the annual coaches’ conference at Douglas College. I’d completed my BCRPA strength and conditioning certification, and I was even a certified kettlebell instructor.

I thought I knew a lot about fitness.

I was wrong.

The CrossFit methodology flew in the face of everything I had been taught. It questioned the truths that I had come to believe.

Who is this ignorant blowhard? I wondered as I began my deep dive into his fringe approach to fitness training.

But CrossFit founder Greg Glassman was not ignorant. He had looked at the same data and reached a different conclusion.

Where we zigged, he zagged.

He had no respect for dogma. What he wanted was results. Quantifiable, repeatable results. Where we clung to theories, he demanded evidence. And on paper, at least, he made a compelling case.

When you come into conflicting worldviews, you can adopt the one that makes you comfortable, or you can put them to the test.

I did the latter.

Yes, I started following CrossFit programming in my garage gym not because I believed in it, but because I was determined to prove Glassman wrong.

He wasn’t.

Over the next three months, I experienced the most profound fitness outcomes in my life to that date. And those would be nothing compared to the results I experienced later in 2008 when I finally hired a CrossFit coach and joined group classes.

Like I said earlier, results do not require belief.

But the question remained: why?

Why did the CrossFit program contradict the accepted fitness industry standards of the day and yet produce unparalleled fitness outcomes?

Why was it so effective?

The CrossFit Methodology: Three Principles That Explain Why It Works

CrossFit’s recipe for fitness is not complex. Here it is:

Constantly varied functional movements performed at high intensity.

Simple. Elegant. Effective.

But why?

To understand the answer, we need to look at each of those three principles.

1. Constantly Varied: Why Your Body Needs Different Challenges

Constantly varied is not the same as random.

That is a mistake a lot of fitness “experts” make when looking at CrossFit programming from the outside in.

There are very intentional programming protocols underlying the constantly varied prescription. But we don’t need to get into all that here.

What we want to know is why constantly varied training produces better results than a tried-and-true routine.

And the answer lies in the well-established SAID principle that every fitness trainer needs to memorize in order to get certified:

Specific Adaptation to Imposed Demands.

That’s why exercise works.

Impose a demand on your body. It adapts.

Lift something heavy. Get stronger.

Simple. Tested. Proven.

This is a principle everyone in the fitness world agreed upon.

But it was Glassman who recognized that training routines suffered from the law of diminishing returns precisely because the SAID principle is true.

Adaptation is the enemy of fitness.

If you train the same way every day, your body acclimates to the stressor, and fewer and fewer adaptations are required.

Glassman cut against the grain when he determined that if the SAID principle is true, then the fastest way to accelerate fitness outcomes is to vary the training stimulus such that each workout provides your body with a novel challenge.

Duh!

Why didn’t we think of that?

It was right there in the acronym staring us in the face. It was obvious once you saw it. We just didn’t see it.

Some trainers still don’t.

Probably because, as human beings, we find comfort in the familiar. We like predictable things and are frightened of the unfamiliar.

The constantly varied prescription makes CrossFit both wildly effective and unpalatable to the masses.

But think about what fitness is supposed to prepare us for.

Life doesn't organize its physical demands into neat, predictable routines. One day you're lifting something heavy. The next you're climbing stairs, carrying groceries, chasing a child, or trying to catch yourself when you trip.

If the goal is to develop broad physical capacity rather than become exceptionally good at one narrow task, it makes sense to train across a broad range of demands.

That's the logic behind constantly varied training.

2. Functional Movements: Why Training the Whole Body Makes Sense

Functional movements are full-body compound movements that mimic the way your body is designed to move in nature.

They are unique in their ability to move large loads, long distances, fast. They also require a core-to-extremity activation sequence.

It is hard today, more than 20 years after the shake-up CrossFit produced in fitness, to recall the state of the industry at the time.

We were focused on bodybuilding-style isolation movements.

We broke down exercises by body part, trying to train them separately as if they were disconnected and not intended to move together.

We’d isolate the biceps with bicep curls, the forearms with wrist curls, the calves with calf raises.

We would perform body-part splits.

Mondays were chest, shoulders and triceps. Tuesdays, back and legs. Wednesdays, we’d do abs and cardio.

So, it took three hours of training spread across three days to hit our whole body.

CrossFit’s answer was a Monday morning Fran.

Forty-five thrusters and 45 pull-ups performed in 15 minutes or less, and you’d already hit every muscle group, gotten your cardio workout, and done more work than a regular gym bro got done in three days, in less time than it took him to warm up.

It is hard to overemphasize what a profound departure this was from the state of the fitness industry at the time.

And there are still people who resist it.

Not because it isn’t effective. The CrossFit Games proved beyond all reasonable doubt the efficacy of Glassman’s game-changing methodology.

People still resist adopting CrossFit because, let’s face it, Fran sucks.

Three hours of lateral raises, pec deck and lat pulldowns spread across three days is a lot easier to bear than the thought of Fran waiting for you in the gym Monday morning.

But there's another reason functional movements matter, particularly as we age.

The movements we need to remain strong, capable and independent are the same fundamental movement patterns we train in CrossFit.

Squatting. Hinging. Pushing. Pulling. Carrying. Getting ourselves up off the ground.

These are not arbitrary gym exercises. They're the physical skills of everyday life.

When we train them, we're not just building muscles. We're building the capacity to keep doing the things we want and need to do, whether we're 25, 45 or 75.

That, to me, is what functional fitness should be about.

3. High Intensity: Why How Hard You Work Matters

Because intensity is hard.

And it is intensity that amplifies the training effects of your workout.

Intensity is not volume.

Intensity is power.

Load × Distance ÷ Time.

Intensity is how much load you moved, how far, how fast.

Beer keg. Flight of stairs. How quickly can you get the keg up the stairs?

There is a lot of confusion about what intensity is. Some people mix up volume with intensity.

A marathon is long. A marathon is hard. A marathon is NOT intense.

A 100-metre sprint is intense.

And this is important to understand because the science is increasingly demonstrating that our ability to produce power is a powerful indicator of health and longevity.

Think about that for a moment.

As we age, we don't just lose muscle mass. We also lose the ability to produce force quickly. And that ability matters enormously to our independence.

It's what helps us climb stairs, rise from a chair, recover our balance and respond to the unexpected physical demands of life.

Strength matters. Power matters. And preserving both is an important part of extending our health span—the years of our lives spent healthy, capable and independent.

But Glassman intuited the importance of intensity already in 2005 when he said:

"Intensity is the independent variable most commonly associated with maximizing favorable adaptation to exercise."

And here's something else worth understanding: high intensity is relative.

What constitutes high intensity for an experienced CrossFit athlete is not the same as what constitutes high intensity for a beginner or an older adult returning to exercise.

The point isn't that everyone should lift the same weight or finish a workout in the same time.

The point is to challenge each person at an intensity appropriate to their current capacity.

That's where good coaching comes in.

A good coach understands the intended stimulus of a workout and knows how to adjust the movements, loads and demands so that each athlete can experience an appropriate challenge.

The workout may look different from one athlete to another. The underlying training principle remains the same.

And that's one of the beautiful things about CrossFit. The methodology doesn't have to change just because the athlete does.

You Don't Have to Believe in CrossFit for It to Work

That’s it.

The CrossFit recipe is as simple as that:

Constantly varied functional movements performed at high intensity.

Oh, I know, some folks refuse to believe it. Even in the face of evidence to the contrary.

Glassman predicted this too. He calls it invincible ignorance.

The thing is, you don’t need to believe in it in order to enjoy the benefits.

Like gravity, CrossFit training will transform you no matter how skeptical you are.

I didn’t believe in it myself.

But 21 years later, here I am preaching the stuff.

Because there is nothing like measurable, repeatable results to change your mind and transform your body.

And if you're skeptical, good.

Ask why. Question the assumptions. Examine the methodology. Put it to the test.

That's how I got here.

Want to Understand CrossFit? Start Here.

Read the following articles, and you will understand more about fitness than most of the non-CrossFit trainers in the world.

Seriously.

I’ve done the NCCP and BCRPA coursework. I’ve read the ACE textbook. I’ve attended the conferences.

These are the foundational resources that changed how I think about fitness:

• What Is Fitness? — Greg Glassman's foundational explanation of how CrossFit defines and measures fitness.

• Foundations — The principles underlying CrossFit's approach to training.

• What Is CrossFit? — An introduction to the methodology.

• CrossFit Recipe — A video explanation of the three-part prescription.

• Understanding CrossFit — A deeper exploration of the methodology.