The Imperfect Training Block: When Ultramarathon Preparation Doesn't Go to Plan

I am writing this Guide from inside the problem rather than after it.

Last year I was dealing with a bone stress injury, and this year I was making great gains training for the Kosci Miler. I finally started to feel like everything was moving in the right direction, then I developed a shin splint and all of that changed.

The obvious physical problem is I am no longer accumulating the training I expected, but there is a mental problem sitting beside it as well. You start looking at the calendar, counting the sessions you have missed, wondering how much fitness you are losing and trying to work out how much training you can somehow squeeze back in once you are able to run properly again.

I do not yet know exactly what this means for Kosci, which is one reason I wanted to write this now rather than after the story has a neat ending.

That sounds obvious when you are looking at somebody else's training block, it is much harder when it is your own race getting closer.

The perfect training block probably does not exist

A long ultramarathon build creates plenty of opportunities for something to get in the way.

Injury, illness, work, family, travel, bad weather, fatigue and life in general do not care what TrainingPeaks says you were supposed to do on Tuesday.

That does not mean consistency is unimportant, it clearly is. A large study using more than 15 million logged activities from almost 300,000 recreational marathon runners found that longer periods without training were associated with slower race times, and disruptions later in the block were associated with a larger performance cost than similar disruptions earlier in training.

But that same research also makes another point that is easy to forget when you are the injured runner, training interruptions are common among people who still make it to race day.

The useful question is not whether your training block is still perfect, because once something has disrupted it that question has already been answered.

The useful question is what the disruption actually changes.

What actually happens to fitness when training is interrupted

Fitness is not a switch that goes from trained to untrained because you missed a week.

Detraining is real, but it is gradual and it depends on what stopped, for how long, what level you were at beforehand and whether you were still able to do other training.

A 2022 systematic review and meta analysis of 21 studies found that VO2 max declined after both short and longer periods of complete training cessation. The average reduction was about 3.9% during short term detraining and about 9.4% during longer term detraining.

Those numbers need some context.

They are averages across different athletes and sports, they describe training cessation rather than every possible version of an interrupted running block, and VO2 max is only one part of ultramarathon performance. They do not tell an individual runner exactly what has happened to their fitness and they certainly do not translate directly into a percentage change in a 100 mile finish time.

There is also a difference between stopping completely and reducing training.

A review looking at how little training is required to maintain performance found that substantial reductions in training volume can preserve endurance performance for surprisingly long periods when some training stimulus remains. The authors were careful to point out that the evidence is much stronger in general populations than in trained athletes, so I would not turn that into a prescription for an injured ultrarunner.

The practical point is simpler, lower volume is not automatically the same thing as zero fitness.

Missing training is not a debt you have to repay

This is probably the part I have to remind myself of most.

The original plan says you should have completed a long run, a hill session and another full week of mileage, you missed them, so when running becomes possible again there is a very strong temptation to start moving those sessions forward and trying to catch up.

The problem is that the calendar moved forward while you were injured as well.

A 30 kilometre long run that belonged six weeks ago does not automatically belong next Tuesday just because there is an empty box beside it.

The training load you missed is gone. Trying to compress it into the remaining block changes the training plan, sometimes quite dramatically, and if the interruption happened because of an injury the tissue that caused the interruption may be the least prepared part of your body for that sudden catch up.

That may mean fewer long runs than you wanted, less race specific volume or a different peak week. It may also mean that the original race target needs to change.

None of those things are improved by pretending the missed weeks are still sitting there waiting to be completed.

Maintain what you safely can

An injury that limits running does not always mean every form of training has to stop, although what is appropriate depends entirely on the injury and the advice you have been given.

Cycling, pool running, swimming or other low impact options can sometimes maintain an aerobic training stimulus while reducing the specific mechanical load that running creates.

A 2026 systematic review and meta analysis looked at cross training between running and cycling. Across the seven included randomised studies it found no clear statistically significant difference in VO2 max or short distance running performance between running and cycling interventions, but the evidence base was small, heterogeneous and included older training protocols.

So I would not read that as proof that cycling is interchangeable with running, particularly for an ultramarathon where your legs still have to tolerate many hours of impact, climbing and descending.

I would read it more cautiously, if an injury allows some other form of aerobic work, that work may still be useful.

The aim is to preserve what can reasonably be preserved while the injured area catches up, not to prove that you can still train hard.

Return based on readiness, not the old calendar

The training plan knows what date it is, it does not know whether your body is ready to resume the training that was written for that date.

That difference matters.

A 2024 scoping review looked specifically at returning to running after tibial bone stress injury. It found that the available evidence is not especially strong, with much of the guidance coming from reviews and clinical commentary rather than high quality trials, but several themes were consistent.

Before running was reintroduced, the literature commonly looked for resolution of symptoms during walking and daily activity, clinical assessment of tenderness, strength and loading capacity, and whether contributing factors had been addressed. Return to running was generally progressive and individualised, often beginning with walk run intervals, with distance or duration rebuilt before speed and intensity.

The same review also made a useful point about the famous 10% rule, it is not generalisable to every runner or every bone stress injury.

That review is specific to tibial bone stress injury, so it should not be used as a return plan for every shin problem, tendon issue or muscle injury.

The broader principle is the useful part, recovery should be based on the injury, symptoms, function and the runner in front of you, not on how urgently the race calendar wants you back.

Stop turning every run into a test

The first few runs after an interruption can become mentally exhausting because every one of them starts carrying far too much meaning.

A good run feels like proof that everything is fixed and the original race plan is back on, a bad run feels like proof that months of work have disappeared.

Neither conclusion is particularly useful.

One run is one run.

The return is better judged as a trend, can you tolerate the load, are symptoms stable, is the volume progressing, are you recovering normally, and can you repeat the work rather than merely survive one session?

This is also where confidence can lag behind physical recovery. Return to sport research repeatedly identifies fear of reinjury, confidence and psychological readiness as part of the process, although much of that evidence comes from other sports and injury types rather than ultrarunning.

That matters because being cleared to run and trusting the body enough to run normally are not always the same thing.

Separate the race from the original race goal

One of the easiest traps is treating the original race target and the race itself as the same decision.

They are not.

You may have entered the race with a particular finishing time in mind, a pacing strategy, a level of training you expected to complete and maybe a fairly clear idea of how race day would look.

An interrupted block may change some of that without automatically removing the race from the calendar.

There is a meaningful difference between changing the goal and ignoring the problem.

If the original 30 hour target is no longer supported by the training, forcing that target onto race day does not restore the missed fitness. It simply asks the current runner to execute the plan of a different runner.

Rebuild the plan from where you are now

Once the training block changes, I think the planning question needs to change with it.

Start with what is true now, how much running are you tolerating, what training has been preserved, what remains uncertain, how much time is left, what are the specific demands of the race and what does the medical or rehabilitation advice allow?

Then build forward from there.

This is where I would rather have a conservative plan that can improve if the next few weeks go well than an aggressive plan that assumes every future week will be perfect because the previous ones were not.

For an ultra, race specificity matters as well. Aerobic fitness is only part of the job, you also need the musculoskeletal tolerance for long hours on your feet, climbing, descending, eating while moving and whatever terrain the race is going to throw at you.

Cross training may help preserve the engine, it cannot guarantee that the chassis is ready for a mountain 100 miler.

The mental side of an interrupted block is real

Injury does something strange to the calendar.

When training is going well, race day can feel a long way away, once you cannot run properly every week suddenly looks important and every missed session feels larger than it probably is.

There is also frustration because the problem is not always under your control. You can be doing the rehabilitation, sleeping, eating properly and making sensible decisions while still watching the original plan drift further away.

Return to sport research shows that fear of reinjury, confidence and psychological readiness can influence how athletes experience the return process. That evidence is not specific to ultrarunners, but the basic experience will be familiar to anyone who has come back from an injury and spent the first few runs listening for every sensation.

I think the useful response is the same one I use in No Pity Party, acknowledge the frustration, then move into the part you can actually influence.

You cannot make the missed weeks disappear, you can follow the rehabilitation properly, maintain what is safe to maintain, avoid turning the return into a panic driven catch up block and keep reassessing the race with better information as it arrives.

What this means for me and Kosci

Right now I do not need to know the ending.

I know the training block I expected to have is no longer the training block I have. I also know I had a decent base before the shin problem arrived, and I know there is still time for the situation to change in either direction.

The useful job now is to get the shin issue under control, maintain whatever training is sensible while that happens, return to running progressively, then judge Kosci from the runner I actually am as race day gets closer.

What I do not want to do is let anxiety about lost training create the next injury by trying to force six weeks of work into three.

If the training comes back well, the race plan can be rebuilt around that.

If the original time goal no longer makes sense, the goal can change.

If the evidence eventually says the race itself is the wrong decision, then that decision has to be available as well.

None of those answers need to be invented today.

Sometimes the race itself has to change

There is a point where adapting the plan stops being enough.

If the injury has not resolved, the return to running is not progressing, race specific loading cannot be rebuilt in time, or a clinician is concerned about the risk of continuing, then the sensible decision may be to change distance, defer the race or not start.

There is no useful formula that says missing a certain number of days automatically means you should withdraw. The research is nowhere near specific enough for that, especially in ultramarathons where race distance, terrain, cutoff structure and individual experience vary enormously.

The decision is better treated as a risk management problem, which is also how return to sport consensus statements frame it, the athlete, clinician and coach combine the current medical picture, functional capacity, sport demands and the consequences of getting the decision wrong.

What the research says

The research is useful, but there is no study that can look at one interrupted ultramarathon block and tell you whether that runner should race.

The strongest evidence helps answer smaller questions.

Training disruptions can affect race performance. A 2023 analysis of 292,323 recreational marathon runners found that training breaks of at least seven days were associated with a roughly 5 to 8% slower marathon time compared with the same runners' less disrupted builds, with longer and later disruptions generally carrying a larger cost. This was marathon data, not ultramarathon data, it only included runners who made it to race day, and the researchers did not know whether each disruption was caused by injury, illness or something else.

Detraining is measurable but not immediate collapse. A 2022 meta analysis found an average VO2 max reduction of about 3.9% during short term training cessation and 9.4% during longer cessation. These are pooled averages across trained athletes and complete or substantial detraining periods, not a prediction for one runner who may still be cross training.

Reduced training can preserve more than runners sometimes expect. A 2021 review found that endurance performance can often be maintained with substantial reductions in training volume when some training intensity is preserved, although the authors noted that athlete specific evidence was limited. For somebody returning from injury, that finding should not be interpreted as a reason to force high intensity running before the injury is ready.

Cross training can preserve an aerobic stimulus, but the transfer is not perfectly understood. A 2026 meta analysis of running and cycling studies found no clear between group differences in VO2 max or running performance, but only seven trials were available and the confidence intervals were wide. That is encouraging enough to support cross training as a useful tool when medically appropriate, not strong enough to call cycling and running interchangeable.

Return to running should be individualised. A 2024 review of tibial bone stress injury guidance found common criteria around symptom resolution, pain free walking, functional loading, strength and contributing factors, followed by a gradual return that often used walk run progression and rebuilt distance before speed. The authors also noted that much of the evidence was low level and the widely quoted 10% progression rule is not generalisable to every runner.

The psychological return matters as well. Recent systematic review work on psychological readiness after injury shows that confidence, fear and perceived readiness can be associated with return to sport outcomes, even though much of this evidence comes from injuries and sports quite different from ultrarunning.

A practical imperfect training block checklist

Common questions

The training block you actually have

I would obviously prefer to be writing this with every Kosci training session completed exactly as planned.

That is not where I am.

The useful part now is not spending the next few weeks comparing reality with the training block I was supposed to have, it is getting the injury right, preserving what I can, rebuilding carefully and then making an honest assessment of the race from the training I actually completed.

The original plan has changed, that does not automatically mean the race is gone.

It does mean the next decisions matter more than the sessions already missed.

Related guides:
No Pity Party
How to Plan Your Race Day for a 100K or 100 Mile Ultramarathon
Ultramarathon Cutoff Strategy: How Much Buffer Do You Really Need?

Research notes and sources

Research snapshot: 28 September 2026. This Guide discusses training interruption, detraining and return to running at a general level. Injury diagnosis and return to running decisions are individual and should be guided by an appropriate health professional when required.