What a taper is actually for

Two weeks out from your race you do what everybody does. You cut your mileage. Big week becomes medium week, medium week becomes small week, and you keep the sessions, because the sessions are what keep you sharp.

Then race day arrives and your legs feel like someone else’s. Flat in the first hour. Nothing there when you go to lift the pace. You spend the next month wondering whether you tapered too much or too little.

A single race cannot tell you whether the taper was too long, too short or the wrong shape. Race-day fatigue has more than one possible explanation.

What is happening underneath

A taper is not rest. Rest is what you do after the race. A taper is a controlled removal of fatigue while you hold on to the fitness underneath it.

Your form on any given day is roughly what you have built, minus what you are currently carrying. A training block adds to both sides. The fitness accumulates slowly and decays slowly. The fatigue accumulates quickly and, crucially, decays quickly too.

That difference in decay rates is the entire mechanism. Stop adding load and the fatigue drains away in one to three weeks while the fitness barely moves. What you are left with is most of what you built, carried by legs no longer buried under it.

A taper cannot make you fitter. It can only stop you arriving buried under the block that did.

The final weeks offer a chance to shed accumulated fatigue. They are a poor time to test unfamiliar training or to make up a missed block.

The mistake

Volume is how much work you do. Intensity is how hard or fast you do it. Frequency is how often you train. A shorter session can preserve intensity while substantially reducing the amount of demanding work.

Keeping some intensity is compatible with doing much less work.

Keeping the same pace for fewer repetitions is different from keeping the full session. So is shortening an easy run. Assess the total dose, including strength work and descents, rather than treating one type of running as free of fatigue.

Meta-analyses in competitive and endurance athletes support reducing training volume while maintaining intensity and frequency. See Bosquet et al. (2007) and Wang et al. (2023). These group findings guide a taper; they do not establish the best prescription for every runner or mountain ultra.

Apply that distinction to your own context. A familiar, brief effort can preserve pace without preserving the usual dose. Pain, illness, unusual fatigue and the demands of the event may require a different approach; a generic taper should not override them.

How long

Published studies often examine tapers of roughly one to three weeks. The appropriate duration depends on the athlete, event and preceding training. Evidence from shorter endurance events does not establish one ideal duration for a mountain hundred.

The individual variation around those numbers is bigger than most plans admit. Some people need a long taper and feel wonderful. Some go stale in ten days and race best off a short sharp one. Age matters, training age matters, and what you did in the block matters.

Which is why the useful thing to do is not to look for a better number.

Write down how you feel, this time

Your taper is a controlled experiment you will run maybe two or three times a year, and almost nobody records the result.

Note how you felt in the last ten days. Note the day the heaviness lifted, if it lifted. Note whether you felt sharp at day four and stale by day ten, or flat until day twelve and then suddenly good. Note what you actually did, not what the plan said.

Do that three times and you will know your own taper better than any generic prescription, because you will have three data points from the only athlete who matters. Do it zero times, which is what most people do, and you will be guessing again next year.

What it feels like when it is working

The middle of a taper is a strange and unsettling place, and knowing that in advance is most of the battle.

Some runners report heaviness or restlessness as training decreases. Those feelings alone do not establish whether the taper is working. Record them alongside sleep, symptoms and what you actually did.

Do not dismiss pain as a normal part of tapering. New, persistent or worsening pain deserves attention, including advice from a clinician when appropriate. A training score cannot clear you to run.

And you will feel like you are losing fitness. You are not. Not in two weeks. This is the single most common reason people sabotage a good taper by adding a session in the last week, and it is worth knowing in advance that the feeling is a liar.

The good sign, when it comes, has nothing to do with feeling fast. It is a familiar easy run suddenly feeling easier than it should for the pace. That is the fatigue draining out. If that has happened two or three days before the race, you are in good shape.

How we handle it, including the part we got wrong

Trailwise reduces the proposed training dose during a taper and checks it against the training it follows. The exact reductions and session rules are product design choices. They are not proof that a taper will suit every athlete or guarantee a race result.

There is also a check that a taper week can never carry more load than the training weeks it follows. That sounds obvious to the point of being insulting. It was not obvious to our first plan generator, which under some combinations of race distance and block length would produce a taper week that outweighed several build weeks, purely because the arithmetic allowed it. We found it, we wrote a test for it, and now a taper that exceeds what came before it fails a check rather than reaching a runner.

I mention it because it is the kind of error that is invisible when it goes wrong. A slightly too big taper week does not look wrong on a calendar. It looks like a normal week. You only find out on race day, and by then you will blame your legs.

Trailwise is not a medical device. Neither is it a replacement for a doctor or a physiotherapist. Trailwise flags what is worth a conversation. It does not diagnose, and it will tell you when it does not know.