Zone 2 built a cult in cycling. On riders over 45, published training-distribution research says too much of it is why FTP stops moving. Here is the corrected plan.
Zone 2 works.
Nobody serious about cycling training will tell you it doesn't. The physiology is airtight. Mitochondrial biogenesis. Fat oxidation. Capillary density. It builds all of it.
The problem is what happened next.
Zone 2 became a cult. And the cult, like every cult, over-corrected.
By 2024, a significant chunk of amateur endurance culture had convinced itself that 80 to 90% of ALL training should be strict Zone 2, with the remaining 10 to 20% being either "quality" or nothing much at all.
For a 32-year-old with 15 hours a week and years of race history, that ratio might be defensible.
For a 51-year-old with 8 hours a week and a slow-moving FTP? It is quietly ruinous.
The training-intensity-distribution literature is much older than the Zone 2 fad. Stephen Seiler has been publishing on it since the early 2000s. Marco Rosenblat's 2019 review in the Journal of Strength and Conditioning Research is the canonical modern breakdown.
The finding, condensed: polarized training (roughly 80% easy, 20% hard, very little middle) beats a threshold-heavy plan for well-trained young athletes with high total volume.
The word doing the load-bearing there is volume.
Seiler's own numbers assume around 10 to 15 hours a week. At that volume, 80% Zone 2 is still 8 to 12 hours of Zone 2. That's a lot of stimulus.
At 6 hours a week, 80% Zone 2 is 4.8 hours. That's not a mitochondrial adaptation plan. That's a slightly elevated resting metabolism.
Two physiological realities work against the older amateur applying the pro plan.
TCW covered this in detail: masters cyclists recover 30 to 40% slower than under-30s. Two hard sessions a week is the ceiling. Sometimes one.
That is fine. It only breaks the model if the rider believes the pro plan calls for one very hard session and 15 hours of Zone 2 around it. Because there are no 15 hours of Zone 2 in a working masters rider's week.
After 40, VO2 max drops roughly 1% per year without targeted intervention.
Endurance stays. Threshold power holds surprisingly well. But peak oxygen uptake, the ceiling that decides how hard you can go on any climb over 3 minutes, quietly disappears.
Zone 2 does nothing to defend VO2 max. Only intensity does.
Our own primer on how to increase VO2 max so your hard efforts feel easier walks through the specific protocols.
Dr. Peter Attia has publicly criticized the "just do Zone 2" framing on multiple podcasts, pointing out that his own aggressive Zone 2 block was paired with weekly VO2 max intervals, not instead of them.
Dr. John Mandrola, a cardiologist and lifelong cyclist, has written more critically. His stated position: masters riders taking on very high volumes of moderate steady-state work are at elevated risk for atrial fibrillation without a matching benefit in top-end performance.
That doesn't mean Zone 2 causes afib. It means the trade-off is worse than the dogma admits.
For a rider aged 45 to 60 with 6 to 9 hours a week, the honest ratio is closer to 65% easy, 25% tempo/sweet-spot, 10% hard.
That translates to:
That's it. No 5-hour ride. No third hard session. No heroism.
The tempo band is the critical addition. Modern Zone 2 evangelism treats sweet-spot as "grey zone" and forbids it. That framing works for pros with 20+ hours a week and 80/20 room to spare. It hollows out the middle of a masters rider's fitness pyramid.
Some masters riders genuinely have used Zone 2 well and gotten faster. Those tend to be riders who came from a heavily interval-based background and had built cardiac-drift issues, over-reached nervous systems, or plain burnout. For them, an 8-month Zone 2 reset actually was the correction.
If you're a 52-year-old who came off a decade of hard-group-ride racing and finally feels good in your body, don't undo that with three interval sessions a week just because a blog said so.
The correction is contextual. So is the dogma.
Take your current week. Count Zone 2 hours. Count everything else.
If your ratio is above 80% pure Zone 2, and you're over 45, and your FTP hasn't moved in 12 months, your problem is not more Zone 2.
Swap one Zone 2 session for 1 hour of sweet-spot (40 minutes at 88 to 93% FTP inside a warmup-cooldown). Add one 25-minute VO2 session (5 x 3 minutes at 115% FTP, three minutes easy between).
Do this for eight weeks. Retest.
You will find the FTP that was "just flat because of aging" starts moving again.
Zone 2 is not the enemy. Dogma is.
Peer-reviewed training-distribution research was never a prescription to do only one intensity. Seiler's 80/20 is not "80% Zone 2, 20% nothing." It is "80% easy, 20% deliberately hard."
Amateurs, particularly masters amateurs, lost the second half of that sentence.
Get it back. Watch your climb times drop.
That's not nothing.
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