A 41-rider study found threshold training produced zero significant VO2 max gain over 9 weeks. The block that did? A polarized split with 11.7 percent gains. Here is why.
Every winter, the same debate shows up in group chats.
Sweet spot or threshold. Which block builds more FTP.
The answer the research keeps giving us is one almost nobody wants to hear.
Neither.
A 2014 study by Thomas Stöggl and Billy Sperlich, published in Frontiers in Physiology, took 41 well-trained endurance athletes and ran them through nine weeks of structured work.
One group did polarized. One did high-intensity intervals. One did threshold. One did high-volume base.
The threshold group gained nothing. The sweet-spot-adjacent group gained nothing.
The polarized group gained 11.7 percent in VO2 max and 17.4 percent in time to exhaustion.
That is a brutal finding for the sweet-spot-vs-threshold industry. Let us walk through why.
What The Study Actually Tested
Stöggl and Sperlich split well-trained athletes into four buckets.
High Volume Training (HVT) rode easy for most of the block. Mostly Zone 2, nothing above threshold.
Threshold Training (THR) sat at or just below FTP for the bulk of hard efforts.
This is the sweet-spot zone cyclists usually mean when they say "sweet spot."
High Intensity Intervals (HIIT) hit short, hard VO2 efforts.
Polarized (POL) spent 80 percent of training time in Zone 1 to 2 and 20 percent in Zone 5. Almost nothing in the middle.
After nine weeks, only two groups improved. Polarized took the biggest gains across almost every variable. HIIT came second. Threshold and high volume essentially stood still.
That is the piece most sweet-spot defenders skip.
Why Threshold Alone Stalls
The intuition behind sweet spot is seductive. If FTP is the goal, train close to FTP. Repeat.
The problem is adaptation. Training at 88 to 94 percent of FTP (classic sweet spot) sits in a physiological middle ground where you accumulate fatigue almost as fast as hard VO2 work, but you do not stimulate the mitochondrial and cardiac adaptations that volume and real VO2 efforts drive.
You end up tired without the gains that justify being tired.
For time-crunched riders, sweet spot feels productive.
Every session is uncomfortable. Every file looks dense. But the body treats it as a kind of grey-zone purgatory: too hard to recover from, too easy to push VO2.
If you have been doing six weeks of sweet spot and your FTP has not moved, this is why.
What A Real Polarized Block Looks Like
The structure the Stöggl study used was unglamorous.
Two hard sessions a week. The rest easy.
The Two Hard Sessions
Each hard day was VO2-max work. Think 4 x 8 minutes at 105 to 110 percent of FTP, three minutes rest. Or 6 x 5 minutes at 110 to 115 percent, three minutes rest.
These sessions should feel awful by interval three. If they do not, you are not at VO2.
The Rest Of The Week
Zone 2. Real Zone 2. 65 to 75 percent of FTP, nose breathing possible, conversational for hours.
Most self-described Zone 2 rides are actually tempo.
The difference matters.
The polarized model only works if the easy days are genuinely easy.
When Sweet Spot Actually Works
Sweet spot is not useless. It is just misused.
For a rider with under five hours a week of total training time, the sweet-spot zone becomes a reasonable compromise. The polarized model needs volume to work.
If you cannot ride long and easy for 10-plus hours a week, you lose the aerobic base-building half of the polarized equation.
In that case, time-crunched structured work at sweet spot still outperforms junk miles.
Sweet spot is also a legitimate base-builder in the final six weeks before an A-race, where sharpening threshold tolerance matters.
Outside those two windows, it is a losing bet.
Where This Falls Short
The Stöggl study used well-trained athletes. If you are new to structured training, almost any block will work for a while, because the untrained body responds to stimulus.
Nine weeks is also a short window.
Some sweet-spot defenders argue that longer blocks (16-plus weeks) do show FTP gains the Stöggl protocol missed.
The data on that is thinner.
And individual response varies. A small minority of riders respond to threshold work better than to polarized, probably due to mitochondrial density differences and genetic variation in fast-twitch recruitment. If you have run both and sweet spot genuinely moved your FTP, keep doing it.
For the typical rider staring at a dropping FTP after two sweet-spot blocks, though, the data is pretty clear. Change the structure.
A Four-Week Template That Beats Sweet Spot
Try this before your next sweet-spot block.
Monday: Easy spin, 60 to 90 minutes Zone 2.
Tuesday: Hard session. 4 x 8 minutes at 108 percent FTP, three minutes rest.
Wednesday: Easy, 60 to 90 minutes Zone 2.
Thursday: Hard session. 5 x 5 minutes at 113 percent FTP, three minutes rest.
Friday: Rest, or 45 minutes recovery.
Saturday: Long Zone 2, 3 to 4 hours.
Sunday: Zone 2, 90 minutes to 2 hours.
Repeat for four weeks. Deload week five. Retest FTP at week six.
If you have the volume to ride 10-plus hours a week, this block consistently outperforms sweet spot in trained riders. The Stöggl data predicts it. Thousands of amateur training logs confirm it.
Final Thoughts
The sweet spot versus threshold debate is a false choice. It assumes those two zones are the only tools in the box.
They are not. And the data says they are not even the best ones for most trained cyclists.
Polarized asks for something harder than sweet spot: real suffering on hard days, real restraint on easy days.
Most amateur riders cannot do the restraint part. They turn Zone 2 into tempo and HIIT into threshold, and end up back in the grey zone where nothing improves.
If your FTP has been stuck, the fix is not switching from sweet spot to threshold. It is switching from grey-zone purgatory to genuinely hard, genuinely easy, on alternating days.
The best cyclists in the world train this way for a reason.
