When to Start, How Long and When to Stop

Marathon training is an exercise in timing.

Long runs, threshold sessions, race-pace work, recovery and tapering all need to arrive at the right point in the training cycle. Altitude training is no different.

The question isn't simply whether sleeping at altitude can benefit a marathon runner. It's when to start, how much exposure to accumulate, and when to reduce or stop altitude before race day.

Get the timing wrong and an athlete may arrive at the start line still adapting to altitude or carrying unnecessary fatigue. Get it right and altitude can sit alongside the marathon program without compromising the quality of the running itself.

This guide looks at how to build simulated altitude into the final stages of a marathon preparation.

Why Marathon Runners Use Altitude

The marathon is overwhelmingly aerobic.

The ability to transport and utilize oxygen efficiently therefore plays an important role in performance, alongside running economy, lactate threshold, fueling, muscular durability and pacing.

One of the primary objectives of prolonged altitude exposure is to stimulate adaptations involved in oxygen transport.

Reduced oxygen availability activates the body's hypoxic response, including increased erythropoietin signalling. With sufficient exposure—and adequate iron availability—this can contribute to increases in red blood cell volume and haemoglobin mass.

Haemoglobin is particularly relevant because it transports oxygen from the lungs to working muscle.

But altitude training should not replace marathon training.

The objective is to add an altitude stimulus without compromising the training that actually prepares an athlete to run 42.2 kilometres.

This is one reason the Live High, Train Low (LHTL) model is particularly attractive.

The athlete accumulates altitude exposure during sleep and recovery, then completes key running sessions at lower altitude where pace and training quality can be maintained.

Research across altitude-training protocols supports physiological and performance adaptations from sufficiently long exposures, although the magnitude of response varies considerably between athletes and protocols.

When Should You Start Altitude Training Before a Marathon?

For most runners using simulated altitude sleep, altitude shouldn't begin during race week.

Think in weeks, not days.

A practical marathon altitude block generally begins approximately:

6–8 weeks before race day

This provides time for:

Week 1: acclimatization
Weeks 2–5: sustained altitude exposure
Final 1–2 weeks: reduction/taper and race preparation

The exact timing depends on the athlete, previous altitude experience and the rest of the marathon program.

An athlete who has never slept at altitude should generally allow more time for gradual acclimatization than someone who has completed several previous blocks.

The key principle is consistency.

Altitude adaptation is driven by accumulated exposure rather than occasional high-altitude nights.

Don't Start at Maximum Altitude

One of the easiest mistakes is assuming that higher altitude automatically means greater benefit.

It doesn't.

The altitude needs to be high enough to provide an appropriate hypoxic stimulus while still allowing the athlete to sleep and recover properly.

A first-time user might therefore begin around:

1,500m simulated altitude

and gradually progress according to individual response.

As acclimatization develops, altitude can progressively increase toward approximately:

2,000–2,500m

rather than immediately setting the system to the eventual target.

This is particularly important during marathon preparation.

Training load may already be high. Long runs are getting longer. Marathon-pace sessions are becoming more demanding.

Poor sleep caused by an overly aggressive altitude progression defeats the purpose.

The First Week: Acclimatization

The first week should therefore be conservative.

A runner might begin around 1,500m and gradually increase toward approximately 2,000m as sleep and physiological response stabilize.

During this period, monitor:

• sleep quality
• resting heart rate
• HRV
• overnight SpO₂
• respiratory response
• perceived recovery
• training quality

This is where altitude should become individualized rather than prescriptive.

Two runners sleeping at exactly 2,500m may experience quite different physiological stress.

The number displayed on the altitude system tells you the environment.

It doesn't tell you how the athlete is responding to it.

Weeks 2–5: Building the Altitude Dose

Once acclimatized, the objective shifts from increasing altitude to accumulating consistent exposure.

For many athletes, this means sleeping at approximately 2,000–2,500m for around 8–10 hours per night.

Over four weeks, eight hours per night produces:

224 hours of exposure.

Ten hours produces:

280 hours.

This cumulative dose is much more important than chasing extremely high simulated altitudes.

Existing Live High, Train Low research has commonly used prolonged daily exposures over multiple weeks, with studies showing changes in haemoglobin mass and other endurance-related measures.

The marathon program itself should continue.

Easy running remains easy.

Threshold work remains threshold work.

Long runs remain specific to the athlete's marathon preparation.

The altitude exposure happens predominantly while the athlete sleeps.

That's the fundamental advantage of LHTL.

The Biggest Mistake: Sacrificing Training Quality

Altitude isn't the training program.

It's an additional physiological stimulus.

If an athlete's sleep deteriorates, resting heart rate rises substantially, recovery declines or key sessions begin falling apart, increasing altitude further isn't necessarily productive.

The appropriate response may actually be to reduce the altitude.

This becomes increasingly important as the marathon approaches because the value of high-quality race-specific training rises.

The final long runs and marathon-pace sessions are too important to compromise simply to accumulate another few hundred metres of simulated altitude.

Iron Matters

There is another prerequisite marathon runners should take seriously.

Iron availability.

Producing additional red blood cells requires iron.

An athlete attempting to stimulate erythropoiesis while iron deficient may therefore substantially limit the response they're trying to create.

This deserves particular attention among endurance runners because running itself can contribute to iron loss, and female endurance athletes are especially susceptible to iron deficiency.

Altitude should therefore be considered within the athlete's broader physiological picture rather than used in isolation.

If iron status is a concern, appropriate blood testing and clinical guidance should precede a serious altitude block.

Oxygen Coach: Measuring the Athlete, Not Just the Altitude

This is where altitude training is starting to change.

Historically, altitude programs were prescribed largely according to location and duration:

2,500m for four weeks.

But two athletes can complete exactly the same altitude protocol and respond differently.

Oxygen Coach is designed to bring the athlete's physiological data together with their altitude exposure.

Rather than recording only:

8 hours at 2,500m

the objective is to understand what happened to the athlete during those eight hours.

Relevant measures can include:

• altitude exposure
• SpO₂
• heart rate
• HRV
• sleep
• training load
• previous altitude exposure
• acclimatization history
• blood markers

Over time, this creates a much more useful picture of an athlete's response than altitude alone.

For a marathon runner, that means altitude can become another measurable component of the training block rather than something occurring separately from it.

The goal isn't to sleep as high as possible. It's to find an altitude dose the athlete can adapt to while continuing to recover and train effectively.

When Should You Stop Altitude Before the Marathon?

This is where the strategy becomes more individualized.

There isn't a universally established single “perfect” number of days between altitude and competition.

Athletes respond differently after returning to normal oxygen conditions, and training fatigue, altitude history and the nature of the competition all influence the outcome.

For a first-time altitude user targeting a sea-level marathon, a conservative strategy is to complete the primary altitude block before race week and allow the final taper to prioritize freshness.

A practical framework might look like this:

14 days before race day

The major altitude accumulation phase is essentially complete.

Training volume is beginning to decrease.

10–7 days before race day

Begin reducing the hypoxic stimulus if that is part of the athlete's established protocol.

Training becomes increasingly focused on maintaining race readiness while removing accumulated fatigue.

Final week

The priority becomes sleep, recovery, fueling and maintaining familiarity with race pace rather than generating new physiological adaptations.

Your existing altitude block has already done its work.

This is not the time to suddenly increase altitude.

Box Altitude's existing From Altitude to Finish Line guide goes deeper into managing this final 14-day transition.

What If the Marathon Itself Is at Altitude?

That's a different problem.

If the race is being held substantially above the altitude where the athlete normally lives, the objective isn't simply to generate potential sea-level performance adaptations.

It's also acclimatization to the race environment itself.

Race elevation, arrival timing and the altitude used during the preparation block therefore need to be considered together.

Someone preparing for a sea-level marathon in London has a different requirement from an athlete racing a mountain marathon above 2,000m.

Altitude should always be programmed around the actual event.

A Simple Eight-Week Marathon Altitude Framework

For a runner targeting a priority marathon, the overall structure might look like this:

This shouldn't be interpreted as a universal prescription.

An experienced altitude responder may use a different schedule. A first-time user may progress more slowly. An athlete preparing for a high-altitude event requires a different strategy again.

Individual response matters.

Altitude Should Fit Around the Marathon — Not the Other Way Around

Perhaps the most important principle is that altitude should support the marathon program.

Not dominate it.

A runner still needs to accumulate mileage.

Complete long runs.

Develop marathon pace.

Fuel properly.

Recover.

Taper.

And arrive healthy.

Altitude provides another stimulus that can sit around those fundamentals.

Technology increasingly allows that stimulus to be delivered without requiring an athlete to relocate to a mountain training camp.

And platforms such as Oxygen Coach increasingly allow the response to that environment to be measured rather than assumed.

That creates a more sophisticated question than:

“What altitude should I sleep at?”

The better question is:

“What altitude exposure can I adapt to while still completing the marathon training that matters?”

For serious marathon runners, that's where altitude training becomes useful.

 

For overnight exposure at home, explore the Sleep Cloud altitude tent or an integrated Altitude Bedroom System.