Athletes who run altitude blocks face two practical questions about persistence. When does the peak performance window land after redescent? How long do the gains last before declining back to baseline? Both questions determine how a block integrates with the racing calendar, and both have specific answers in the literature that competitors typically gloss over with vague reassurance.

This article walks through the actual decay curve. The 7 to 14 day peak window, the 3 to 4 week elevation persistence, recent work that suggests Hbmass may persist longer than the conventional model predicted, and the practical implications for athletes scheduling races and subsequent blocks across a season.

The Conventional Decay Curve

The working model from the AIS-affiliated literature describes a four-phase pattern after a properly dosed altitude block.

The first phase covers days 0 to 7 post-redescent. Hbmass continues to rise slightly across the first several days as the marrow completes its production cycle from the EPO signal generated late in the block. The athlete typically experiences residual ventilatory adjustment and lingering training fatigue. Performance during this window is variable and often slightly below expectation, despite Hbmass continuing to elevate.

The second phase covers days 7 to 14 post-redescent. The peak performance window typically lands here for most athletes. Hbmass is at or near its maximum value, the residual fatigue has cleared, and the body has reacclimatised to sea-level oxygen. This is the window most experienced altitude athletes target for priority races.

The third phase covers days 14 to 28 post-redescent. Hbmass remains elevated above baseline but begins a gradual decline. EPO has normalised, the hypoxic stimulus is gone, and red blood cell production is back at maintenance levels. Performance remains good but the peak has passed.

The fourth phase covers days 28 to 42 post-redescent. Hbmass declines toward baseline as red blood cells produced during the block reach the end of their natural lifespan. Most athletes return to pre-block Hbmass levels by week 5 or 6.

The Garvican et al. 2012 study in Scandinavian Journal of Medicine and Science in Sports, which tracked 13 World-Tour-level cyclists through a 3-week altitude camp at 2,760m, documented the rise phase cleanly: 2.9 percent Hbmass increase by day 11 and 3.5 percent by day 19. The subsequent decline tracks the conventional model.

What Recent Research Has Refined

The conventional decay curve assumes red blood cells produced during the block follow standard turnover kinetics, with the typical RBC lifespan of approximately 120 days governing the decline. Recent work has begun to question this assumption.

A 2025 study in the American Journal of Physiology - Heart and Circulatory Physiology on persistent Hbmass elevation in elite swimmers found that Hbmass remained elevated 10 days after a 4-week live high-train high camp at 1,850m, with the persistence partly attributable to prolonged erythrocyte survival. The mechanism appears to involve reduced RBC senescence markers in altitude-trained athletes, suggesting that the red blood cells produced during a block may persist meaningfully longer than the standard turnover model predicts.

The Kettunen et al. 2023 paper in Scandinavian Journal of Medicine and Science in Sports documented a 4.2 percent Hbmass increase across a 4-week normobaric LHTL+H protocol at 2,250 to 2,500m, with the elevation persisting beyond the immediate post-camp window in a subset of athletes.

The practical implication is direct. Athletes who have run multiple blocks across a season may carry Hbmass elevation longer than the conventional 4 to 6 week model predicts, particularly when iron status and training quality have been preserved through the block. The conventional model is not wrong. It may simply describe a faster decline pattern than what serious altitude athletes actually experience.

Why the Decline Happens

The decay is driven by physiology rather than detraining in the conventional sense. Three mechanisms combine.

Red blood cell turnover proceeds at its natural rate. RBCs produced during the altitude block enter the circulating pool and follow approximately 120-day lifespans. Without the hypoxic stimulus to maintain elevated production, the new RBCs are not replaced as they age out. The decline is gradual rather than sudden because the new cohort of cells exits the pool over weeks rather than days.

EPO normalises within days of redescent. The signal that drove the production peak during the block disappears within 7 to 14 days, and red blood cell production rate returns to maintenance levels. The marrow stops accelerating production, but the cells already produced continue to circulate and deliver oxygen.

Plasma volume expansion partially compensates for the haematocrit decline. As Hbmass declines toward baseline, plasma volume typically expands, which preserves total blood volume but dilutes haemoglobin concentration. The athlete's haematological profile gradually returns to its pre-block configuration without a sudden performance drop.

This is why the decay is described as a return to homeostatic baseline rather than a loss of fitness. The athlete has not become less aerobically fit. The temporary haematological elevation that the protocol produced has reverted to the natural set point.

Race-Scheduling Implications

The persistence curve shapes how serious altitude athletes structure their racing calendars.

For the single-priority-race calendar, the working model is straightforward. Run a 4 to 6 week block ending 7 to 14 days before the priority race. Race inside the peak window. Allow the haematological elevation to decline naturally afterward, and resume normal training without forcing a second peak.

For the dual-race calendar, where two priority events fall within 4 to 6 weeks of each other, a single block can sometimes peak both. The first race lands in the days 7 to 14 window. The second race lands in the days 28 to 42 window during the gradual decline. Performance for the second race is typically slightly below the first but still meaningfully elevated above baseline.

For the multi-block season, where athletes target three or more priority races spread across the year, the practical model is to run separate altitude blocks separated by 8 to 12 weeks of normal training. The 8 to 12 week interval allows the haematological response to return fully to baseline, giving subsequent blocks a clean dose-response curve to work against. Block stacking too tightly, with 4 to 6 weeks between consecutive blocks, sometimes produces diminishing returns as the athlete enters the second block on an elevated baseline.

Box Altitude has covered the practical race-week protocol for the final 14 days before a priority event in a separate article. The persistence curve sits behind that guide as the underlying science.

Individual Variation Is Substantial

The conventional 7 to 14 day peak window describes the population average. Individual response timing varies substantially around that mean.

A subset of athletes peak inside days 3 to 5 post-redescent, with the residual fatigue clearing rapidly and the haematological elevation expressing immediately as performance. These athletes typically have efficient ventilatory reacclimatisation and minimal post-block fatigue.

The largest group peak in the conventional days 7 to 14 window. This is the safest target for first-time altitude users and for athletes without prior data on their individual response timing.

A smaller subset peak inside days 21 to 28 post-redescent, with the response expressing more slowly as both ventilatory adjustment and accumulated training fatigue take longer to clear. These athletes often benefit from running blocks with longer pre-race tapers built in.

The recent persistence literature suggests that some athletes, particularly experienced altitude users with multiple blocks under their belt, may retain elevated Hbmass through days 28 to 42 with measurable performance benefit. This subset is the focus of the prolonged erythrocyte survival research, and the practical implication is that experienced altitude athletes may have more flexible race-scheduling windows than first-time users.

The Mujika, Sharma, and Stellingwerff 2019 narrative review on contemporary altitude periodisation in Sports Medicine consolidated this individual-variation framework. Trial blocks remain the only reliable way to characterise individual response timing, and the data from those blocks should inform subsequent programming.

Practical Implications

The persistence curve translates into several working rules for athletes scheduling structured altitude blocks.

Start the block 5 to 8 weeks before the priority race. A 4 to 6 week block plus a 7 to 14 day post-block taper window lands the peak performance window inside race week. Athletes targeting full-distance Ironman or multi-stage events may extend the lead-in to 6 to 8 weeks to accommodate longer race-specific tapers.

Descend with deliberate timing. The descent date is the start of the post-block window. An early descent (10 to 14 days pre-race) is safer for first-time altitude users and athletes with sensitive ventilatory adaptation. A later descent (5 to 7 days pre-race) is sometimes used by experienced athletes who have characterised their response timing across previous blocks.

Race inside the peak window. Days 7 to 14 are the safest target for the first major race after a block. Subsequent races within 4 to 6 weeks can typically be raced inside the gradual decline window, with the understanding that performance will be slightly below the peak race.

Schedule subsequent blocks 8 to 12 weeks apart. The interval allows full haematological return to baseline and a clean dose-response curve for the next block. Compressed scheduling is possible for athletes pursuing aggressive multi-block seasons, but the diminishing returns risk grows with shorter intervals.

Cameron Wurf, the Australian cyclist and Ironman record-holder, has applied these scheduling rules across a long career where altitude exposure is integrated as a structural feature of the season rather than a single experimental block. The persistence curve is the underlying science that makes that integration work.

Box Altitude's partnership with the Queensland Academy of Sport connects the brand to the AIS-affiliated tradition that produced much of the persistence and periodisation literature referenced in this article.

The Bottom Line

Altitude gains last approximately 4 to 6 weeks after a properly dosed block, with the peak performance window landing days 7 to 14 post-redescent and the gradual decline proceeding across the following 3 to 4 weeks. Recent literature on prolonged red blood cell survival in elite altitude athletes suggests that experienced users may carry Hbmass elevation meaningfully longer than the conventional model predicts.

For race scheduling, the working rules are direct. Start the block 5 to 8 weeks before the priority event. Descend 7 to 14 days before race day. Race inside the peak window. Schedule subsequent blocks at least 8 to 12 weeks apart for clean dose-response curves.

For athletes running structured altitude protocols at home, the Sleep Cloud Altitude System delivers the consistent 8 to 10 hour nightly exposure across a 4 to 6 week block, with the Box Altitude App tracking cumulative dose toward the 300-hour benchmark. The protocol fidelity that determines block response also determines persistence: the cleaner the dose, the cleaner the post-block window.

The persistence curve is what turns altitude training from a single-block experiment into a structural feature of an annual training plan. The athletes who run the protocol successfully across multiple seasons are the athletes who use the persistence data to schedule their racing, not the other way around.

View Our Altitude Systems

Medical Disclaimer

The information in this article is for educational purposes only and does not constitute medical advice, diagnosis, or treatment. Altitude training is a physiological intervention affecting the cardiovascular, respiratory, and haematological systems, with individual responses varying by health status, medical history, age, and fitness level. Before commencing any altitude protocol, consult a qualified medical practitioner or sports physician, particularly if you are pregnant, have cardiovascular or pulmonary conditions, haematological disorders, are recovering from surgery or injury, or are taking prescription medications. Box Altitude products are designed for healthy adults and are not medical devices intended to diagnose, treat, cure, or prevent any disease. Pre-altitude blood marker screening should be completed with a qualified clinician before starting a structured block, and any persistent severe symptoms during altitude exposure warrant immediate medical attention. Performance claims reference peer-reviewed scientific literature in healthy athletic populations; individual outcomes vary and cannot be guaranteed.