What Is Functional Fitness — And Is It Right for You?

By: Jesse Carrajat

“Functional fitness” is one of the most used and least defined terms in the industry. So, when I sat down with Jon Little — COO at REP Fitness, a lifter since his teens, and a backcountry hunter who chases elk at 12,000 feet — he opened with the obvious question: what does that actually mean?

What followed was the clearest working definition I've heard. Below are the moments from Stronger Weekly worth your time, with the research that backs them up.

The Definition, Taken Apart and Put Back Together

Little refuses to use the word inside its own definition, so he splits it.

“Fitness can be broadly defined as an object’s ability to perform a task — or in this context, the human body’s ability to execute a task. Functional means capable. So, if you put that together, functional fitness is the body’s ability to be capable. And then you take it one step farther: capable for what?”

“Functional fitness is the body’s ability to be capable for a purpose. And that purpose is largely defined by the individual.”

Why it matters: the definition puts the burden back on you. A professional football player and a marathon runner need almost entirely different capabilities. Both are training functionally. The question was never what is the correct program — it was what are you trying to be capable of?

Worth knowing: the confusion is common. In 2025, an international panel of exercise scientists ran a four-round Delphi study in the Journal of Sports Sciences specifically to define functional training, and concluded that so many definitions coexist that, taken loosely, “Every training approach could be functional.” Little’s version is more useful than the field’s.

Yes, Bodybuilding Counts

Asked whether bodybuilders have “no functional goal,” Little declined the easy answer.

“I think bodybuilding gets a bad rap. I do think standing on stage posing is hard work. Hypertrophy, aesthetics, symmetry, balance — those all matter if you’re going to win a competition that’s largely based on aesthetics. But the physique is real. So, in my mind, that’s functional. For that purpose.”

The Gym Is a Delivery Mechanism, Not the Methodology

“I wouldn’t argue that CrossFit is the Mecca. It’s one of the places you can go to train. You can do the same in a 24-Hour Fitness. Before I started CrossFit, I was doing functional fitness workouts in 24-Hour. I got some weird looks. But the reality is, you can do it anywhere.”

“HYROX is functional fitness. It leans toward endurance versus Olympic lifting and strength movements, but all those elements are there. ATHX, Xenom — all these hybrid fitness competitions qualify. And so does traditional training. I don’t think it fits in a nice, neat little box.”

Context: fitness racing is not a niche anymore. HYROX expects more than two million athletes across 107 race weekends in its 2026/27 season, up from 1.5 million the year prior.

The Honest Limitation: Hypertrophy

I pushed on where CrossFit-style training might leave gaps.

“CrossFit-style workouts are not the best for hypertrophy, because isolation movements are typically not part of the training. If you think about hypertrophy as eight to twelve reps per set focused on a single muscle group to maximize size, you’re not going to find that in a CrossFit gym.”

But Little drew a sharp line between size and strength:

“You can gain muscle mass. When I started CrossFit, I got stronger than I’d ever been across my entire body in a relatively short period of time — and I’d been in a gym most of my life. Hypertrophy, not so much. I didn’t gain weight. I didn’t get bigger. But I certainly felt great and I looked great.”

The fix is layering, not switching. Little points to gyms that program accessory work, powerlifting, Olympic lifting, and gymnastics skill blocks alongside the daily class.

The 70% Rule — The Best Idea in the Episode

I described being cognitively wrecked for two hours after all-out sessions. Little’s answer reframes the whole thing.

“For the day-to-day athlete, it’s about coming back tomorrow. If 70% is my hundred percent for that day, I’m good with that. Because consistency, sustainability — I want to be able to come back tomorrow. I don’t want to be so sore that I can’t fathom getting up and going to the gym.”

Little says that mindset has changed with experience. “When I first started, it was all in, all the time, a hundred percent. Now, after seven years, I’ve learned: that workout’s probably going to wreck me, so I’m going to give it my 80% and I’ll be able to come back on Thursday. And then Thursday I look at that workout and think — okay, that one I can send it.”

“It’s infinitely scalable. Consistency beats short-term effort over time, almost every time.”

Why Any of This Matters: The 12.4-Year Gap

Asked who functional fitness is for, Little said everyone — and then explained why in terms of health span.

“Life expectancy in the United States is mid-seventies. Most people start to fail physically, lose their independence, in their early-to-mid sixties. Maximizing cardio health, maximizing strength performance over time — that’s a way to close that gap.”

“My ideal state: I want to be 84 years old, go hiking with my kids, go home, go to bed, and die. That would be the perfect scenario, because I will have drawn my healthspan and my lifespan to the exact same point in time.”

The data is more damning than the anecdote. Mayo Clinic researchers analyzing 183 WHO member states found the U.S. health span–lifespan gap is now 12.4 years — the widest in the world, up from 10.9 in 2000 (JAMA Network Open, 2024). The global average is 9.6.

And the evidence that training closes it is strong:

• Low cardiorespiratory fitness was associated with roughly five times the risk of death compared to elite fitness in a Cleveland Clinic study of 122,000+ adults — with no ceiling to the benefit (JAMA Network Open, 2018).

• Just 30–60 minutes per week of strength training was associated with roughly 10–20% lower risk of all-cause mortality across 16 cohorts; paired with aerobic work, roughly 40% lower risk (BJSM, 2022).

• Exercise reduced the rate of falls by 23% in a Cochrane review of 81 trials, with balance and functional exercise the most effective category.

If You’re Starting from Zero

Little’s beginner prescription, condensed:

• Get coaching first. “I wouldn’t expect a beginner to know how to write their own program.”

• Build four movement patterns before anything else: squat, deadlift, bench press, overhead press. “Developing those movement patterns is what enables expansion into isolation movements later. I wouldn’t start with barbell curls.”

• Pick cardio you’ll actually do. “If you like riding bikes, ride a bike. If you like running, run. Do something to get your heart rate up.”

• Three to five days a week, with intensity — plus some movement, even a walk, on off days.

• If you split it, treat cardio as active recovery between strength sessions.

And you don’t need a gym.

“You absolutely can do this at home, and I’d argue today it’s easier than ever. Commercial-quality gear for a garage gym is attainable. So is the programming. The point is to find what works for you and start. Do something.”

If You Already Train — You May Not Need to Change Anything

I laid out my own week: four strength sessions, a fartlek run, a long steady-state day, about six hours total. What should I change to go “more functional”?

“I don’t think it’s a change in time, and even the splits, I wouldn’t change. If you’re doing isolation movements, I might shift to compound movements. Beyond that, it depends on the capability you’re trying to build. What you mentioned could also be construed as hybrid fitness — and I don’t draw a big distinction between functional and hybrid. Those terms are interchangeable.”

“If your training protocols meet your goals and are building the capability you want — some of which is time with family, because that is a capability you want to build — then you’re delivering on exactly what works for you.”

The Hydration Mistake Almost Everyone Makes

The most useful story in the episode inverts the standard advice.

“I’ve had experience in the mountains where I’ve actually bonked. That year I was eating normally. I was drinking a ton of water — too much water, as a matter of fact. So much that I was washing all the electrolytes effectively out of my system. I started supplementing with electrolytes on that hunt, and it was like the battery just recharged. Literally within twelve hours, I was 100% back to normal.”

More water was not the fix. More water was the problem.

The science lines up. Dehydration beyond ~2% of body mass measurably impairs cognition — attention takes the biggest hit — across 33 pooled studies (MSSE, 2018). At altitude the demand spikes: respiratory water loss alone can climb by up to 1,900 mL per day in men, plus roughly another 500 mL to altitude-induced diuresis. The CDC reports about 25% of visitors sleeping above 8,000 feet in Colorado develop acute mountain sickness — whose cardinal symptoms, headache and fatigue, look exactly like dehydration.

But Wilderness Medical Society guidelines are explicit: drinking more water has never been shown to prevent altitude illness and can raise hyponatremia risk. The variable isn’t volume. It’s what’s in the water — sodium, potassium, magnesium.

Fueling It

“If you’re getting adequate protein, adequate carbohydrate, adequate fats in the right ratios, then whole foods, minimize sugar. But that’s hard given today’s food systems. So supplementation is, I think for most people, a must.”

On sugar: “It’s inflammatory pressure in the body. You’re going to be more inflamed, more sore, your joints are going to hurt more.”

On sleep: “If you’re going to train that way, you should probably be getting seven to eight hours a night.”

The number worth remembering: a meta-analysis of 49 studies and 1,863 participants found protein supplementation improved resistance-training gains in both size and strength, with benefits plateauing around 1.6 g per kilogram of bodyweight per day — roughly 130g for a 180-pound adult (BJSM, 2018). Source and timing mattered far less than hitting the daily total.

That is where Purist® Grass-Fed Whey Protein (25g of grass-fed whey isolate, NSF Certified for Sport, no artificial sweeteners or added sugar) and Purist® Hydration (510mg sodium, 250mg potassium, 60mg magnesium, zero sugar) are designed to fit — not as a replacement for whole foods, but as the thing that makes the target achievable on a real schedule.

"Capable and Ready"

Little’s closing argument isn’t a study. It’s a Friday.

“Last Friday I hiked a marathon. Twenty-seven miles. I didn’t really train to hike twenty-seven miles. But I got up in the morning, put a pack on, grabbed the dog, and we hiked a marathon. Nine and a half hours.”

“It allows me to have the capability to be the best for my family, the best at work, and the best in the mountains. At any given point.”

“At the end of the day, we want to be as healthy as we can be for as long as we can be. That’s the goal.”

The Takeaway

Start with the question, not the program. What do you want to be capable of? Everything downstream — the split, the gym, the protein target, the electrolytes — is arithmetic once you have answered it.

Listen to the full conversation with Jon Little on Stronger Weekly. [Apple Podcasts] [Spotify] [YouTube]

Shop Purist Nutrition — NSF Certified for Sport, no artificial ingredients.

Jon Little is the COO at REP Fitness, the parent company of Purist® Nutrition. Jesse Carrajat is the host of Stronger Weekly, a health and fitness podcast. This blog was created in partnership with Purist Nutrition. Nothing in this article constitutes medical advice. Always consult a qualified healthcare provider before beginning or modifying any medication or supplement protocol.

This article was reviewed by Rosie Borchert, NASM-CPT, for accuracy.