What Needs to Shift?

Life doesn't send calendar invites for fitness tests. Instead, you get pop quizzes: sprinting for a bus, conquering a stairwell when the elevator quits, or "keeping up" with your kids in what feels like Olympic training.

These aren't just inconveniences. They're your body's performance reviews. 

And the feedback comes in real-time: that universal move of checking your phone at the top of stairs (not for notifications—for dignity 😮‍💨), or perfecting the art of "casual breathing" after chasing down a train.

Or, my personal favourite…the London Heathrow Airport Stress Test ✈️ (where terminal changes are measured in miles, and tight connections separate the fit from the flight-missers).

Your first flight lands late. Your connection is a 10-minute death march across a terminal the size of a small country. You start power-walking like your life depends on it. 

Then you spot your gate, and hit a wall. Chest tight. Legs burning. Your heartbeat drowning out the airport announcements. 💓

For some of us, these moments are already here. For others, they're auditioning for starring roles in your future. They're your body's not-so-subtle way of saying "We need to talk." 🚨

And like most important conversations, this one's better had before you're desperately gasping for air in Terminal B. 😰

These moments of breathlessness aren't just inconvenient, they're a reflection of a poor VO₂ max, your body's maximum capacity to take in, transport, and use oxygen during intense activity.

Medical research has found this measurement so powerful that a VO₂ max in the bottom 25% multiplies your risk of early death fivefold. Being "unfit" by this measure may carry a greater mortality risk than smoking, hypertension, or diabetes.

The good news? Even moving from "poor" to "below average" VO₂ max cuts that risk in half. 📉

The bad news? Let it slide, and your world shrinks in slow motion: stairs feeling longer, destinations feeling farther, life's demands feeling heavier. Your body surrenders, accepting a smaller world as its new normal.

So how do you stop that from happening?

From Steady State to Redline 📈

Improving your VO₂ max—a key predictor of longevity—requires a two-pronged approach.

First, there’s zone 2 training; the slow, steady-state work we covered in Issue #10 that builds your metabolic engine's efficiency. Without it, trying to improve your VO₂ max is like trying to build a penthouse on a shaky first floor.

But life doesn't always let you stay in steady-state.

Sometimes you need to sprint through airports, chase down buses, or climb several flights of stairs without stopping. If you never push your energy system to adapt to these demands, it never adapts to deliver oxygen at full throttle. ⚡

This is where high-intensity interval training (HIIT) comes in—a training method that alternates between intense effort and recovery periods.

HIIT protocols come in many forms, typically involving short bursts of high-intensity effort ranging from 20 seconds to a minute, followed by equivalent rest periods, repeated over multiple intervals. But when it comes to specifically improving VO₂ max, research points to one variant as particularly potent: 4-8 minute bursts of high-intensity efforts that push your lungs to their limits, followed by just enough recovery to convince yourself you can do it again.

Think of your cardiovascular system like a highway:

🚗 Zone 2 training builds more lanes and better connections → Your body creates new capillaries, improves circulation, builds metabolic efficiency. This is your foundation.

🚀 HIIT raises the speed limit → Your heart becomes a more powerful pump, your lungs process more oxygen, your muscles extract every molecule of fuel to handle peak demand.

Turbocharging Your Engine ⚡

These high-intensity intervals rewrite your body's operating manual in three major ways:

❤️‍🔥 A More Efficient Heart

• Your heart learns to push out more blood with each beat, like upgrading from a garden hose to a fire hose.

• This is why elite athletes often have enviably low resting heart rates. Their hearts are strong enough to pump more blood with each beat, so they need fewer beats to get the job done.

🫁 Teaching Your Muscles to Breathe Better

• Your muscles become better at extracting oxygen from your blood, like upgrading from a weak refrigerator magnet to a powerful industrial magnet, pulling more oxygen molecules from the bloodstream. 🧲

• The result? You can maintain higher intensities longer before your muscles wave the white flag. 🏳️

✅ Keeping Your Pipes Young

• Think of your blood vessels like rubber bands. They need to stretch and snap back countless times a day. With age, they get stiff and cranky.

• High-intensity training forces your vessels to expand and contract fully, keeping them flexible.

• Flexible vessels mean your heart isn't fighting against rusty pipes. Your blood pressure stays lower, and your heart has to work less.

• The payoff? Dramatically lower risk of the big three: heart disease, stroke, and dementia. 🎯

Your Next Move

There are many high-intensity interval protocols, but the Norwegian 4×4 is emerging as the gold standard for improving VO₂ max. It’s simple to follow, well-studied, and effective.

🔥 The Norwegian 4×4

🌡️ Warm Up

• 10 minutes of running, cycling or swimming at an "easy" pace.

• Skip this step at your own risk. Your first interval will teach you why every engine needs warming up.

🏁 The Main Event

1. Push hard for 4 minutes → Push to 90-95% of your max heart rate (for a 40-year old, that’s ~170-180 bpm). It's the kind of effort that makes you question your life choices. Your lungs will protest. Let them.

2. Recover for 4 minutes → Slow down to an easy jog or slow pedal, where you start feeling almost human again. 😮‍💨

3. Repeat this cycle 4 times.

Here's what my heart rate looks like during a typical session (yes, I do five intervals instead of four because I’m an over-achiever, or maybe I just love suffering 😒):

😵 How Hard Is “Hard”?

• By minute 3, your legs will stage a mutiny, your lungs will file for divorce, and your brain will start drafting strongly worded letters of resignation. 🥵

• If you can talk, you’re not pushing hard enough.

• No watch? Don’t let that stop you. If you're mentally drafting cease-and-desist letters to this clearly sadistic author, you're in the right zone.

📅 Dosing Your Discomfort

• 1 session per week is enough to see massive gains. Max 2 sessions per week. Your body needs time to forgive you. 🛌