For ten years I was mostly running steady Zone 2.
It’s what every longevity expert recommends. Countless podcasts on zone2 this, zone2 that. Magic drug, miracle on a stick!
I was doing 1,000 kilometers per year, completed multiple half-marathons, and followed all the typical wisdom about building an aerobic base.
And I hiit a wall (haha!)
No matter how many kilometers I ran, my pace stayed the same. Haven’t beaten my PR in years. I was fit and not bad at running.
Half marathons became easy at a 6min/km pace. I was running around Central Park in circles. Literally 😉
But I wasn’t getting faster.
Then I added zone 4 intervals to my routine. Within months, I was 20% faster at 5-7km distances and 15% faster at 10km. I started crushing old personal records while spending less time in low heart rate zones.
Initially it was a simple Norwegian 4×4 protocol: four minutes of hard work, four minutes of recovery, repeated four times.
The difference? High-Intensity Interval Training (HIIT) targets adaptations that my puny zone2 cardio simply won’t reach.
And those short trainings are way easier on my joints!
Now I try to do a 4×4 once a week and do two fast 5k runs around it, where I try to keep my heart rate at the bottom of zone4 to be comfortable there.
What HIIT Actually Does
HIIT alternates short bursts of intense effort (really intense!) with recovery periods. A typical session lasts 20-30 minutes, performed 2-3 times per week, with intervals ranging from 30 seconds to 4 minutes at high intensity[1].
The physiological benefits are significant:
Cardiovascular Adaptation
HIIT improves VO2 max—your body’s maximum oxygen utilization—more effectively than steady-state cardio[1]. Higher VO2 max correlates with lower all-cause mortality and better quality of life as you age.
Metabolic Enhancement
These intervals enhance fat burning and boost metabolism through increased mitochondrial function[2]. Your cells become more efficient at producing energy, which translates to better endurance and faster recovery.
I top it off with some sauna and red light therapy sessions for an extra boost.
Insulin Sensitivity
HIIT improves how your body handles glucose, reducing inflammation markers and supporting metabolic health[3][4]. I bump it up with Apple Cider Vinegar pre-breakfast, and one berberine pill at breakfast.
Time Efficiency
You achieve more adaptation in 20 minutes of intervals than in an hour of zone 2 work. For entrepreneurs and busy professionals, this matters. Trust me, I know.
The Protocol: What Works
The Norwegian 4×4 protocol is the gold standard:
- 4 minutes at zone 4 intensity (roughly 85-95% max heart rate)
- 4 minutes of active recovery (light jog or walk)
- Repeat 4 times
- Total time: ~40 minutes including warm-up and cool-down
My zone 4 starts at 161 bpm. During the work intervals, I maintained a 3:59/km pace. Essentially running around 1 kilometer per work set. The intensity is high enough that conversation is impossible. But that’s fine because I run alone and talking to myself is kinda silly.
And it’s pretty warming up even in the worst months of winter.
The HR reaches my tops around 180-190 (I go higher than the calculation for my age)
Recently, I switched to sustained 5km zone 4 runs. Lower average pace, but the focus shifted to keeping my heart rate above 161 for the entire distance. Both approaches work—the key is intensity and consistency.
Frequency: Every other day when weather permits, with strength training on rest days. I replaced long zone 2 runs with 10-minute zone 2 rowing sessions daily for active recovery.
Environment: Outdoor running works best. I tried replicating zone 4 on a bike and water rower indoors, but couldn’t maintain the heart rate. Something about the biomechanics of running triggers the cardiovascular response needed for true zone 4 work.
What It Feels Like
Early sessions were brutal. Felt like punishment. When I tried 10×1-minute intervals with 1-minute rest, it was even worse. Absolutely soul crushing. Walking out the door on interval days was always with a frowny face.
Then something shifted.
As the speed gains became undeniable, the mindset changed. Now I love these sessions. There’s a metallic taste in my mouth during hard efforts, and I’m tired afterward. But during the run, I feel powerful. Watching myself move 20% faster than a year ago is addictive. The progress becomes self-reinforcing. The pain kinda fades away.
Physically, zone 4 sits in an interesting space. You’re tired, breathing hard, but not in agony. It’s sustainable discomfort. The kind that makes you stronger.
Measurable Changes Beyond Speed
Heart Rate Recovery: Improved from 32 bpm drop in the first minute post-exercise to over 50 bpm. This is a strong indicator of cardiovascular fitness and autonomic nervous system health.
Resting Heart Rate: Stayed consistently low at 40-44 bpm (though zone 2 work had already driven this down over the years).
Recovery Capacity: Some days I feel ready to run zone 4 back-to-back, though I stick to every-other-day scheduling with strength training on off days.
Energy Levels: Noticeably higher throughout the day, especially when I take midday workout breaks.
Core Strength Impact: I trained core significantly more this year, which improved running economy and made holding zone 4 pace easier. HIIT + strength work compounds.
Integration with Work
I work on a computer all day, running multiple companies. The best time for HIIT? Mid-day, around noon. Although the last few weeks I’ve been actually going at it fasted around 9am.
But yeah, much prefer mid day, after breakfast and a small bit of work is already done.
I take a break, run hard for 30-40 minutes, and come back slightly tired but mentally in a good place. The fatigue isn’t demotivating. It’s like I just had a huge coffee. Switching from sitting to intense movement and back creates variety that makes both work and training less monotonous.
Super early (sunrise) morning or late evening sessions don’t work for me. Intertwining fitness with work hours is the strategy. Variety over rigid scheduling.
Beginner Protocol: Start Small
If you’ve been doing only zone 2 cardio and want to add HIIT, start with a modified Norwegian 4×4:
- Warm up (10 minutes easy pace)
- 4 minutes zone 4 (hard but sustainable)
- 4 minutes recovery jog
- 4 minutes zone 4
- Cool down (10 minutes easy)
That’s it. Just two work intervals. Eight minutes of hard effort total.
This establishes your baseline pace. Over weeks, add a third set, then a fourth. The progression should feel challenging but not traumatic.
What to avoid:
- Jumping straight to 10×1-minute sprints
- Doing HIIT on consecutive days without recovery
- Training through injury or exhaustion
- Letting dread prevent you from trying
The attitude shift is real. At first, you’ll hate it. Then you’ll see progress, and that progress makes you love it. Just push through the first 3-4 sessions.
Risks and Considerations
HIIT is tough on you. Without proper form and stretching, injury risk can be big[5]. Overtraining is also real if you don’t respect recovery days. Beginners should start with lower volume and build gradually. I’ve had the overtraining crashes a couple times and don’t recommend it 😛
If you have heart conditions or haven’t exercised regularly, consult a doctor before attempting high-intensity intervals.
Don’t do HIIT immediately before heavy strength training sessions; it can blunt adaptation. Separate them by several hours or schedule on different days. Best on different days. I alternate cardio and strength and do plenty of recovery activities.
The Zone 2 vs Zone 4 Question
Zone 2 builds aerobic base and mitochondrial density. Zone 4 builds power, speed, and VO2 max. You probably need both.
But if you’ve been doing only zone 2 for years and hit a plateau, zone 4 is the missing variable. The fastest gains come when you introduce the stimulus your body hasn’t adapted to yet.
I don’t regret the ten years of zone 2 running. They built my foundation. But adding zone 4 unlocked adaptations that steady-state work never could.
Bottom Line
High-Intensity Interval Training works. The science is solid, the time investment is minimal, and the results are measurable. If you’re plateaued on zone 2 cardio, two 4×4 sessions per week will change your performance within months.
Start small. Track your pace. Watch the numbers improve.
Then enjoy being 20% faster.
References
[1] Effects of High-Intensity Interval Training on VO2 Max – PubMed, 2023
[2] HIIT and Metabolic Rate Enhancement – PubMed, 2024
[3] Mitochondrial Benefits of HIIT – Mayo Clinic, 2022
[4] HIIT and Inflammation Reduction – Cleveland Clinic, 2023
[5] Risks of High-Intensity Exercise – American Heart Association, 2021
[6] HIIT Impact on Insulin Sensitivity – NIH, 2024
Listen & Learn More
Dr. Rhonda Patrick – Micronutrients, Exercise & Aging
Dr. Andrew Huberman – How to Build Endurance
Dr. Mike Israetel – HIIT Training Breakdown
Want to track your own protocols? Download Longevity Deck — the free app with 100+ evidence-based health protocols, including HIIT training templates, heart rate zone calculators, and progress tracking.
