The grey zone: is riding at 'medium' really wasted training?

"Junk miles." "No man's land." "The grey zone." Whatever the phrase, the claim is the same: riding at a moderate, uncomfortable-but-manageable pace is the worst thing you can do with a training session. Too hard to recover from, too easy to drive adaptation, and therefore a waste of everybody's afternoon.

It is the most confidently repeated idea in amateur endurance training, and it is built on a real and respectable body of research. It is also routinely stretched well past what that research actually showed, to the point where riders now feel guilty about a tempo ride that would have been entirely unremarkable in any elite training week you care to examine.

So: is the middle wasted? The honest answer is that it depends on what it is replacing, and that the studies everyone cites were not testing the question most people think they were.

Where the idea came from

The origin is descriptive rather than experimental. In the early 2000s, researchers started quantifying how elite endurance athletes actually distributed their training intensity. The consistent finding across rowers, runners, skiers and cyclists was that roughly three quarters of sessions sat below the first lactate threshold, a meaningful minority sat above the second, and comparatively little sat in the middle.

That observation got a name — polarised training — and then a normative turn. If the best athletes in the world spend little time in the middle, perhaps the middle is where training goes to die. A small number of intervention trials followed, and several of them supported the idea: in trained runners, spending more time genuinely easy produced better outcomes; in trained cyclists, six weeks of a polarised distribution beat a threshold-focused one on several measures; in a four-arm comparison across endurance athletes, the polarised group improved most.

This is a legitimate evidence base. The problem is what got done with it.

What the trials actually compared

Look at the bottom bar. That is what "threshold training" meant in most of these studies: around a third of all training time spent between the two thresholds, week after week, for six to twelve weeks. That is not one tempo ride inside an otherwise sensible week. It is a fundamentally different programme in which moderate intensity is the main course.

So when a trial reports that polarised beat threshold, the correct reading is "a week with 15 to 20 percent hard work and very little middle beat a week built around the middle". It is not evidence that adding a tempo session to an otherwise polarised week makes you slower, because nobody ran that experiment.

The picture has also got murkier as more data has come in. A 2019 meta-analysis found in favour of polarised over threshold distributions but flagged the small number of studies and the variation between them. A larger 2024 review comparing polarised against other distributions reported limited evidence that polarised is reliably superior. And in 2022 the journal that publishes much of this work ran a formal point-counterpoint under the headings "Polarized Training Is Optimal for Endurance Athletes" and "Polarized Training Is Not Optimal for Endurance Athletes". When two groups of serious physiologists are still arguing it out in print, the version circulating as settled fact on the internet is running ahead of the field.

The pyramid in the room

The single most awkward fact for the strong version of the grey-zone claim is that pyramidal distributions are extremely common among elite endurance athletes, and a pyramid is polarised training with the middle put back in. Reviews of highly trained distance runners describe a pyramidal shape through the general preparation phase, becoming more polarised closer to competition. Cycling looks similar.

A pyramidal week might be 80 percent easy, 15 percent moderate and 5 percent hard. That 15 percent is grey zone by any definition, and it belongs to athletes at the top of the sport. If the middle were genuinely junk, it is hard to explain why so much of it survives in the training of people whose living depends on getting this right. We go through the two shapes in more detail in polarised vs pyramidal training.

A naming problem that causes half the confusion

Much of the argument online is two people using the same word for different intensities. In the three-zone model that the polarised literature uses, zone 2 is the grey zone — between the two lactate thresholds, roughly tempo to just under threshold. In the seven-zone power model most training apps use, zone 2 is easy endurance riding and the grey zone is around zone 3.

So "do your zone 2" means "ride easy" to one rider and "ride tempo" to another, and both are correct within their own model. If you are not sure which one your plan is speaking, three zones, five or seven is the piece that sorts it out, and it is worth five minutes before you argue with anyone about junk miles.

When the middle is right, and when it is not

Notice the pattern. Every genuine mistake in that right-hand column is about displacement. Moderate intensity is not harmful in itself; it is harmful when it takes the place of something you needed more. That is a much more useful rule than a blanket ban, because it tells you what to check: not the intensity of the ride you just did, but what it cost the rest of the week.

The thing that actually is junk

There is a version of the grey-zone critique that is straightforwardly correct, and it has nothing to do with planned tempo sessions. It is about drift.

Most amateur riders do not choose to ride in the middle. They intend to ride easy and end up at 75 percent of threshold because there was a hill, or a headwind, or somebody in the group went to the front. Over a week, an easy ride that quietly becomes a tempo ride costs you recovery you had budgeted and gives you a stimulus you had not planned for. Do that three times and your two hard sessions are compromised.

That is the real cost, and it is a discipline problem rather than a physiology one. It is also the reason easy riding is genuinely easier indoors, where the resistance does not argue with you: Moveee Indoor holds a target in ERG mode and records the whole power stream, so you can check afterwards whether Tuesday's endurance ride actually stayed where you put it. Outdoors, staying in zone takes deliberate effort and a willingness to let people ride away from you on climbs.

What to do with all this

• Protect the easy days first. Almost every version of the evidence agrees that a large majority of training should be genuinely easy. If something has to give, it is not this.
• Make your hard days properly hard. The original criticism was aimed at sessions that were intended to be intense and were not. Two real quality sessions a week beats four ambiguous ones — the case made in how many hard days a week.
• Then place moderate work deliberately, if it earns its place. Specific preparation for a long event, or a way to get useful load into a short week. Planned, on purpose, in a known quantity.
• If your week is short, stop apologising for tempo. The 80/20 finding was described in athletes with far more hours than you have. Whether it scales down is an open question, not a settled one. Sweet spot, threshold or polarised covers the trade-off for riders training around a job.

The grey zone is not a hole in the intensity scale that swallows training. It is a perfectly ordinary region of effort that becomes a problem when it arrives by accident and displaces something better. Ride there on purpose, in a sensible quantity, having decided what it is for — and the word junk stops applying.