Vo2 max 37 at 42 — 12 weeks of zone 2 got me to 41
I ran the numbers on my own Garmin data. My VO2 max was 37 mL/kg/min at 42 — bottom 25th percentile for my age. That's "fair" but barely. I'd been doing mostly HIIT-style workouts (OrangeTheory, 4x/week) for two years.
Switched to zone 2 cycling: 3x/week, 45 minutes, heart rate 125-135 bpm. That's 65-72% of my max HR. No HIIT, no weights, just steady-state aerobic work. Did this for 12 weeks straight.
Results: VO2 max went from 37 to 41. That's a 10.8% increase. My resting heart rate dropped from 68 to 62. Sleep quality score on Garmin went from 72 to 81. I also stopped getting winded carrying groceries up three flights of stairs.
The mechanism: zone 2 builds mitochondrial density and capillary networks in slow-twitch muscle fibers. HIIT doesn't do this as effectively because it relies on anaerobic pathways. I'm not saying ditch HIIT entirely — just that zone 2 deserves more respect than it gets.
Next test: 8 more weeks to see if I can hit 43.