For years, I told my clients to limit or avoid cardio altogether.
And for the right reasons. Too much steady-state cardio, stacked on top of an already stressed nervous system, will spike cortisol, eat muscle, and teach the body to hold onto fat rather than burn it.
I’ve written about this lots. And I still believe it. But eventually, “be careful with cardio” turned into “cardio is the enemy,” and that’s not what I meant, and it’s not what the research says either.
There’s a type of cardio that actually boosts health, longevity, and fat loss.
It’s called Zone 2, and it might be the most underused tool in fat loss after 40.
The Key: Most of Your Training Should Feel Too Easy
Here’s the part that surprises almost every client I introduce this to.
Elite endurance athletes — the ones with the best engines and the leanest bodies on the planet — spend roughly 80% of their training time at low intensity. Only about 20% is spent hard. This pattern has been documented across many sports, and it’s now one of the more consistently replicated findings in performance research.
But most people do the opposite. They spend the bulk of their cardio in the “grey zone” — too hard to be easy, not hard enough to be a real interval — and then wonder why they feel tired all the time and can’t move the needle on body composition.
It’s an easy trap to fall into, and one I have to constantly remind myself of.
And when we’re talking about low intensity here, I mean Zone 2 or lower. A pace where you could hold a full conversation easily, roughly 60-70% of max heart rate. It should feel too easy to even count as exercise.
Why Zone 2 Actually Burns Fat (and Most Cardio Doesn’t)
Training at this low, sustainable intensity does something higher-intensity cardio can’t — it builds mitochondrial density.
Mitochondria are the engines inside your cells that convert fuel into usable energy, and the more of them you have, the better your body gets at pulling energy from fat instead of sugar, at rest and during everyday movement.
That’s a different mechanism from “burning calories” during a workout. It’s teaching your body, at the cellular level, to become a better fat burner all day long, not just during the 45 minutes you’re training.
Push too hard, too often, and you skip this adaptation entirely. Your body uses glycogen and stress hormones instead, which is exactly the pattern that keeps so many of my clients stuck.
The Importance of Acknowledging Life Stress
Most of my clients over 40 already have a lot of stress in their lives.
They have a demanding job, a family, and not enough sleep. Add hard, glycolytic cardio on top of that, and you’re asking an already-stressed system to handle more stress. Cortisol stays elevated and fat loss stalls, particularly around the midsection.
Zone 2 does the opposite. Because it sits below the threshold that triggers a significant stress response, it supports your nervous system, rather than adding more stress. Clients consistently tell me these sessions feel restorative rather than depleting. They don’t feel like a “workout”.
For someone who’s already managing a lot of stress, this is crucial. It might be the difference between a habit that lasts and one that gets abandoned in 6 weeks.
Where the 20% Comes In
None of this means we avoid hard efforts altogether.
The other 20% — short, genuinely hard intervals — is what raises your ceiling: your VO2 max, your cardiovascular capacity, your ability to handle a true emergency effort. Research on cardiorespiratory fitness has linked higher VO2 max to a significantly lower risk of all-cause mortality in some of the largest cohort studies we have on the subject.
The two aren’t competing strategies. They’re different tools for different jobs. Zone 2 builds the everyday engine and trains fat metabolism. Short, hard efforts stretch your capacity. Most people just never learn to tell them apart.
Why I Avoided Cardio for a Decade — and Why I Stopped
For about 10 years, my training looked almost the same every week.
Strength training, short and hard interval sprints, and lots of walking. Steady-state cardio didn’t have a place in it, and honestly, I didn’t miss it. I’d seen what excessive cardio did to clients who over-relied on it, and I built my own training around avoiding it entirely.
What I hadn’t fully separated was the difference between excessive cardio and the right cardio, done at the right intensity.
Becoming a hybrid athlete — trying to hold onto hockey-level power and strength while adding running volume for the first time — is what forced me to actually look at Zone 2 properly instead of lumping it in with everything I’d spent a decade avoiding. And the more I read and the more I tested it on myself, the more it became obvious I’d been leaving something on the table.
The mitochondrial part alone changed my thinking. A decade of sprints and strength work builds power and muscle extremely well, but it doesn’t build the aerobic base that makes your body efficient at using fat for fuel in daily life, not just during a workout. Zone 2 does that.
It’s also remarkably low-impact, which matters more with every year that passes and every hockey injury I’m still managing. And it’s one of the few forms of training that improve general cardiovascular fitness and longevity markers without adding stress to a system that’s already carrying plenty.
So I added it in. My easy sessions stayed genuinely easy — slower than what felt “worth it” at first. My hard sessions stayed hard and short. And I started noticing the kind of general capacity you don’t get from sprints and lifting alone: less joint wear, steadier energy, and recovery that felt easier to manage around hockey and life.
I’m now building this into my clients’ programs — not as a replacement for the strength training and structured intervals that already work, but as the missing aerobic layer underneath them. For most of them, like me, the hard part isn’t doing the work. It’s trusting that “easy” is actually doing something.
How to Apply This for You
Zone 2, in practice: pick a pace where you could hold a full conversation without gasping. If you can’t talk, you’re not in Zone 2 — you’re just doing moderate cardio again.
Aim for this to make up the majority of your cardio — 3–4 sessions a week, 30 to 45 minutes, is a reasonable starting target.
The hard 20%: one, maybe two sessions a week of short, genuinely difficult intervals — 3 to 5 minutes at a pace you can only hold for that window, with equal or longer recovery between rounds.
Everything in between is the zone to spend the least time in.
Pair this with your strength training rather than instead of it. This isn’t a replacement for lifting. It’s the other half of the engine.
If this resonated, here’s what to do now:
Wondering how to stay lean without tracking everything you eat? See exactly what I eat in a day to stay at 14% body fat year-round, without counting calories or living in a deficit:
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P.S. I’m working with a small group of high-performers over 40 who want to:
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