Same sessions. Same effort. Nearly double the results. That's what separates the riders who come out of winter measurably faster from the ones who spent three months sweating on the turbo with nothing to show for it. The difference isn't talent or even volume. It's structure.
Most riders clip in, put something on the telly, and ride at whatever intensity feels about right for forty-five minutes. Same thing Thursday. Same thing Sunday. Three months of that and your FTP hasn't moved, your motivation is in pieces, and you're blaming the turbo for a problem it didn't cause. The riders who actually improve over winter are following a plan that looks, on paper, almost boring. And that's precisely why it works.
Why most indoor training fails
The grey zone is where winter fitness goes to die. It's the intensity that feels like you're working — your breathing is up, your legs are burning a bit, you're sweating buckets — but it's not hard enough to trigger the high-end adaptations you need and not easy enough to build your aerobic base without costing recovery. Professor Stephen Seiler has spent two decades studying intensity distribution in elite endurance athletes, and his data keeps pointing to the same conclusion: athletes who spend most of their time in the middle improve less than athletes who polarise their training between truly easy and truly hard.
What most people do is ride every indoor session at this moderate-hard intensity because it feels productive. What actually works is something that feels counterintuitive — making most of your indoor sessions so easy they barely feel like training, and making the hard ones so hard you couldn't hold them a second longer. Seiler's 80/20 principle isn't a rough guideline. It's what emerges again and again when you study the training logs of athletes who keep getting faster.
The indoor environment makes this worse, not better. Outdoors, you get natural variation — a descent, a tailwind, a coffee stop — that breaks up the effort and accidentally creates some easy time. On the turbo, there's no descent, no tailwind, and no reason to soft-pedal, so the temptation is to push the whole time. Every session drifts into that moderate-hard wasteland. Tim Kerrison built Team Sky's entire training philosophy around the idea that controlling intensity precisely is what separates good training from noise, and nowhere is that control more available — and more frequently wasted — than on a smart trainer sitting in your spare room.
The intensity map you actually need
Before the sessions, you need the framework. Dan Lorang, who coaches Primož Roglič, has talked about how periodisation means knowing which energy system you're targeting in every single session and why. Random suffering doesn't count. Each session in your indoor week should have a specific purpose, a specific power target, and a specific duration — and the mix between them across the week matters more than any individual session.
Think of it as a menu, not a rota. You have six types of session available to you, each targeting a different piece of the engine. The skill is knowing which ones to pick on which days and, critically, which ones to leave out. John Wakefield, who designs sessions at Bora-Hansgrohe, has made the point that the best coaches spend more time deciding what not to prescribe than what to prescribe. Your winter indoor week should draw from the following six sessions — but you won't do all six in any given week, and trying to is how you end up overtrained by February.
Session one: Zone 2 endurance — the one everyone skips
Set your trainer to 65-75% of your FTP, hold a cadence of 85-95 RPM, and ride for 90 minutes. That's it. No intervals, no surges, no drama. Your breathing should be comfortable enough to hold a full conversation, and if you're gasping between sentences, you're too high.
This is the session that builds your aerobic engine — mitochondrial density, fat oxidation, capillary development — at a cost your body can absorb day after day. It's also the session most riders skip indoors because it feels like a waste of time. It's not. Seiler's work showed that this low-intensity volume is the foundation the entire pyramid sits on, and removing it doesn't free up recovery for more hard work — it removes the base that makes the hard work productive.
The trick to surviving 90 minutes of easy indoor riding is entertainment, not intensity. Put on a film, listen to a podcast, watch a race. The goal is to keep your power in the window and your mind occupied. If you find yourself creeping above 75% because you're bored, you've missed the point.
Session two: tempo — controlled pressure
Three efforts of 15 minutes at 76-87% of your FTP, with 5 minutes of easy spinning between each. Total session time including warm-up and cool-down is about 75 minutes.
Tempo sits just above the endurance ceiling. It's harder than Zone 2 but nowhere near threshold — you should be able to speak in short sentences, but you won't want to hold a conversation. This session develops your ability to sustain moderate power for longer periods, which matters enormously in sportives, group rides, and the opening hours of any long event. It also teaches your body to clear lactate at moderate intensities, which raises the floor under everything else you do.
The danger with tempo is that it sits close enough to the grey zone to slide into it. The difference between 87% and 92% FTP is small on the screen but large in what it costs your body. Be precise. If your FTP is 250 watts, the difference between the top of tempo and the bottom of sweet spot is about 12 watts — that's the gap between a session that builds you up and one that quietly digs a hole.
Session three: sweet spot — the workhorse
Two efforts of 20 minutes at 88-93% of your FTP, with 10 minutes of recovery spinning between them. Total session time is around 70 minutes.
Sweet spot is the intensity that gives you the most training stimulus per unit of fatigue, which is why coaches like Kerrison leaned on it heavily during the winter months at Sky. It sits just below your threshold — hard enough to push significant adaptation in your aerobic system, easy enough that you can recover from it within 24-36 hours and do another quality session the next day.
What matters most about sweet spot: it should feel controlled, not desperate. If you're hanging on by the end of the second 20-minute block, you're probably above 93% and you've crossed into threshold territory. The whole point of sweet spot is that it's sustainable. You should finish feeling like you worked, not like you survived. Two twenties at the right intensity should leave you with the sense that you could have done a third if pushed — that's the sign you've nailed the zone.
Session four: threshold — the ceiling raiser
Two efforts of 15 minutes at 95-105% of your FTP, with 10 minutes of easy spinning between them. Total session time is around 60-65 minutes.
Threshold work raises your FTP, which raises the ceiling everything else sits under. When your threshold goes up, your sweet spot goes up, your tempo goes up, and your endurance pace can stay the same while costing you proportionally less. It's the rising tide that lifts every boat.
This session should feel hard. Not eyeballs-out hard, but the kind of hard where you're watching the clock and properly relieved when the interval ends. Your breathing is heavy, your legs are filling, and conversation is impossible. If you can chat during a threshold interval, your FTP number is wrong and you need to retest.
The 10-minute recovery between blocks is non-negotiable. Don't cut it to 7 minutes because you're short on time. The quality of the second interval depends on the completeness of the recovery — Wakefield has talked about how rushing recovery between efforts is one of the most common session design mistakes he sees in amateur plans. Easy spin, bring the heart rate down, let the legs clear, then go again.
Session five: VO2max — the sharp end
Five efforts of 4 minutes at 106-120% of your FTP, with 4 minutes of easy recovery between each. Total session time including warm-up and cool-down is around 55-60 minutes.
VO2max intervals are the sessions that build your ceiling — the absolute maximum rate at which your body can consume oxygen. They're brutal, they're effective, and they don't need to be long. Four minutes is enough to drive your oxygen consumption to near-maximum, and five repetitions accumulates enough time at that intensity to provoke adaptation. Lorang has talked about how even Roglič's hardest sessions are precise in their dosage — it's not about surviving the most pain, it's about accumulating enough time at the right intensity.
The power range is wide on purpose. A rider with a 250-watt FTP might start the first interval at 300 watts and fade to 270 by the end of the fourth minute, and that's fine. The goal is to keep your power above 106% and your heart rate climbing toward its maximum. If you can hold 120% for all four minutes of every interval, your FTP is probably set too low.
These sessions are where the turbo trainer earns its place. Outdoors, sustaining exactly 4 minutes at VO2max power requires a perfect road — no junctions, no traffic, no gradient changes. Indoors, you set the power and hold it. The controlled environment is made for this kind of work.
Session six: short anaerobic repeats — the top of the pyramid
Eight efforts of 30 seconds at 130-150% of your FTP, with 30 seconds of easy spinning between each. The work block takes only 8 minutes, and the total session including warm-up and cool-down is around 45 minutes.
These short, sharp efforts develop your anaerobic capacity and neuromuscular power — the ability to produce big watts for short periods. They matter for attacks, surges in group rides, and any moment where the pace spikes suddenly.
Don't be fooled by how short the work block looks on paper. Eight rounds of 30 seconds at 130-150% FTP with minimal recovery is deeply unpleasant. The first three feel manageable. The last three feel like someone is sitting on your chest. That accumulation of incomplete recovery is what drives the adaptation.
How to build a winter week
Here's where it all comes together, and where the Seiler 80/20 principle meets the reality of a time-pressed amateur schedule. A well-structured indoor week for a serious amateur might look like this across five sessions.
Monday is a rest day. Tuesday is a hard session — threshold intervals or VO2max work, depending on where you are in your training block. Wednesday is a Zone 2 endurance ride, 90 minutes, easy enough to watch a film. Thursday is another hard session — if Tuesday was threshold, Thursday is VO2max, or vice versa. Sweet spot can slot in here during weeks when you need the stimulus but can't face another round of high-intensity work. Friday is either a rest day or a very easy 30-minute spin if your legs feel good. Saturday is another Zone 2 session or a tempo ride if you're feeling fresh. Sunday is a flex day — ride outdoors if the weather allows, or add a third easy session indoors.
That gives you two hard sessions, two or three easy sessions, and one or two rest days. The ratio of easy to hard time lands close to Seiler's 80/20 split, which is not an accident — it's the distribution that his research, and the practice of coaches like Kerrison and Lorang and Wakefield, keeps converging on.
The mistake most riders make is flipping this structure. They do five sessions, all at moderate-hard intensity, because it feels like they're working every day. But five sessions in the grey zone produces more fatigue and less adaptation than two properly hard sessions and three properly easy ones. The structure that looks lazier on Strava is the structure that actually builds fitness.
What changes across the winter
A winter spent entirely on sweet spot and threshold is not the same as a periodised winter. The early months — November and December for most riders in the Northern Hemisphere — should lean heavily toward endurance and tempo work, with the odd sweet spot session mixed in. This is when you're building the aerobic base that everything else will sit on.
As January and February arrive, the balance shifts. Threshold work becomes a weekly fixture. VO2max intervals appear once a week. Sweet spot moves from a primary session to a supplementary one. The short anaerobic repeats can be layered in during the final weeks before the racing or sportive season begins. Lorang's approach with Roglič follows this same arc — build the base wide, then sharpen the top — and there's no reason the principle changes just because you're doing it in a garage instead of on the roads of Monaco.
The sessions stay the same. The mix changes. That's periodisation stripped to its essentials, and it's the difference between arriving at spring with a broad, deep fitness and arriving at spring with the same FTP you had in October.
The one rule that governs all of this
If there's a single principle that runs through everything Seiler has published, everything Kerrison built at Sky, and everything the best coaches keep coming back to, it's this: easy has to be easy, and hard has to be hard. The middle is where fitness stalls. On a turbo trainer, with a power meter staring you in the face and no external factors to blame, you have every tool you need to get the intensity right. The question is whether you have the discipline to use them.
Most riders don't lack motivation. They lack restraint. They split the difference, ride at 85% for an hour, call it a good session, and repeat it four times a week. That's the recipe for a winter that produces sweat and fatigue and very little else.
The riders who come out of winter transformed are the ones who trusted the structure. They let the easy be easy and the hard be hard, and they let the training do what training does when you stop getting in its way.
If you want the structure, the coaching, and a community of riders who are serious about getting faster this winter, the Not Done Yet community on Skool is where we put this stuff into practice — real plans, real accountability, and riders who'll keep you honest on the easy days.