Altitude training has long been a cornerstone of elite endurance sport preparation, and in recent seasons it has played a defining role in the resurgence of American swimmer Regan Smith. After a breakout junior career that included world records in the 200‑meter backstroke, Smith experienced a transitional period before reemerging as a medal contender on the global stage. Central to that comeback has been a structured altitude training regimen. By examining the physiological underpinnings of altitude exposure and Smith’s specific performance trajectory, we can understand why this method remains one of the most powerful – and most misunderstood – tools available to swimmers.

The Science of Altitude Training: More Than Just Thin Air

Altitude training refers to any period of exercise or residence in environments where the partial pressure of oxygen is reduced, typically at elevations above 1,500–2,000 meters (5,000–6,500 feet). At these heights the body must function with lower oxygen availability, triggering a cascade of adaptive responses that, when properly managed, can enhance sea‑level performance. The key adaptations include:

  • Increased red blood cell mass: The kidney releases erythropoietin (EPO) in response to low oxygen, stimulating the bone marrow to produce more red blood cells. This expands the oxygen‑carrying capacity of the blood.
  • Improved capillary density: Chronic hypoxia promotes the growth of new capillaries around muscle fibers, shortening the diffusion distance for oxygen.
  • Enhanced mitochondrial efficiency: The mitochondria in muscle cells become more efficient at using oxygen to produce ATP, delaying the onset of fatigue.
  • Better buffering capacity: Altitude exposure can increase the body’s ability to manage lactate and acidosis, which is especially relevant for high‑intensity swimming events.

There are several methodological approaches. The classic “live high, train high” model involves both living and training at altitude, which maximizes the hypoxic stimulus but can limit training intensity because reduced oxygen impairs workout quality. Many elite swimmers instead adopt a “live high, train low” strategy: they sleep and rest at high altitude (often using purpose‑built hypoxic living facilities) but travel to lower elevations for their hardest training sessions. This allows them to obtain the hematological benefits of altitude exposure while preserving the ability to swim at race‑quality speeds. Some athletes also use intermittent hypoxic exposure – sleeping in altitude tents or chambers for several weeks leading into major competitions.

The Historical Precedent in Swimming

Altitude training entered mainstream consciousness after the 1968 Mexico City Olympics, held at 2,240 meters. Athletes who had prepared at altitude performed disproportionately well, especially in endurance events. National swimming federations soon began building high‑altitude training centers in places like Flagstaff, Arizona (2,100 m); Mammoth Lakes, California (2,400 m); and Font Romeu, France (1,800 m). The U.S. Olympic and Paralympic Training Center in Colorado Springs (1,850 m) remains a hub for elite swim camps.

Regan Smith’s program, based at the University of Texas under the guidance of head coach Bob Bowman and her personal coach, includes periodic blocks in Flagstaff and at the U.S. Olympic Training Center. Smith also uses altitude tents during phases of the year when travel to high‑elevation locations is impractical. This combination of chronic and acute hypoxic exposure has been carefully periodized around her competition schedule.

Regan Smith’s Career Arc: From Teen Prodigy to Altitude‑Powered Champion

Smith burst onto the international scene in 2019, shattering the world record in the 200‑meter backstroke at the World Championships in Gwangju with a time of 2:03.35. She also set a world record in the 100‑meter backstroke (57.57) earlier that year. At the time she was only 17 years old. However, the delayed 2020 Tokyo Olympics brought a different reality: Smith won silver in the 200‑meter backstroke and bronze in the 100‑meter backstroke, but she did not match her world‑record paces. The four‑year Olympic cycle that followed brought coaching changes, a transfer from Stanford to Texas, and a rededication to the training process.

It was during this period that altitude work became a more central pillar of her preparation. “I started incorporating altitude blocks in 2022 and immediately noticed a difference in how I felt during the last 50 meters of races,” Smith said in a press conference following the 2023 U.S. National Championships. “Even if it’s subtle in practice, the cumulative effect over several months is real.”

Performance Metrics Before and After Altitude Integration

To quantify the effect, we compare Smith’s key event times from the 2021–2022 season (pre‑structured altitude) to the 2023–2024 season (post‑altitude blocks). The data below draws from official results at U.S. Nationals and international meets.

  • 200‑meter backstroke: 2021‑2022 best: 2:05.94 → 2023‑2024 best: 2:03.87 (improvement of 2.07 seconds)
  • 100‑meter backstroke: 2021‑2022 best: 58.30 → 2023‑2024 best: 57.41 (improvement of 0.89 seconds)
  • 200‑meter butterfly: 2021‑2022 best: 2:06.88 → 2023‑2024 best: 2:05.12 (improvement of 1.76 seconds)
  • 200‑meter individual medley: 2021‑2022 best: 2:09.62 → 2023‑2024 best: 2:08.01 (improvement of 1.61 seconds)

While some improvement can be attributed to maturation and refined technique, the magnitude and consistency across multiple events – especially the 200‑meter distances where aerobic capacity is paramount – strongly suggest a physiological adaptation beyond normal gains. Smith also reported fewer “fading” finishes in the final laps of her races, a subjective indicator that aligns with improved oxygen utilization.

Sub‑maximal Effort and Recovery Metrics

Behind the race times, training data collected via heart‑rate variability (HRV) and lactate testing show that Smith’s sub‑maximal aerobic efficiency improved after altitude blocks. Her heart rate at a given pace dropped by an average of 5–8 beats per minute, and her blood lactate levels after identical repeat sets were 0.6–1.1 mmol/L lower. These metrics, while not visible on a results sheet, form the foundation of her ability to hold high speed through the second half of races.

How Altitude Training Produces These Gains: A Detailed Physiological Walk‑Through

To understand why Smith’s times dropped so markedly, we need to follow the oxygen pathway from the lungs to the working muscles. At sea level, the partial pressure of oxygen (PO₂) in arterial blood is roughly 95–100 mmHg. At 2,500 meters, arterial PO₂ drops to about 60 mmHg. This hypoxemia triggers an immediate increase in ventilation and heart rate, and over the course of one to three weeks it stimulates erythropoiesis.

Erythropoietin (EPO) levels typically double or triple within 24–48 hours of exposure to moderate altitude (2,100–2,500 m). This hormone then travels to the bone marrow, where it accelerates the production of red blood cells. Because red blood cells contain hemoglobin, the protein that binds oxygen, the total oxygen‑carrying capacity of the blood increases. A typical response is a 3–5 percent rise in hematocrit (the percentage of blood volume occupied by red blood cells) after three to four weeks at altitude. For a swimmer like Smith, who already has a high baseline hematocrit, even a 2–3 percent boost can translate into meaningful performance gains over the course of a 200‑meter race.

In addition to hematological changes, altitude exposure up‑regulates the expression of hypoxia‑inducible factor 1‑alpha (HIF‑1α), a transcription factor that governs the body’s response to low oxygen. HIF‑1α triggers the production of vascular endothelial growth factor (VEGF), which promotes angiogenesis – the growth of new capillaries. More capillaries mean that oxygen molecules have a shorter distance to travel from the blood to the mitochondria. This adaptation is especially valuable for swimmers, who rely on a high rate of oxygen delivery to the large muscles of the back, shoulders, and arms during repetitive strokes.

Recent research also points to improvements in mitochondrial function. A 2019 study by Dufour et al. in the Journal of Applied Physiology found that four weeks of live‑high‑train‑low training increased the activity of cytochrome c oxidase, a key enzyme in the electron transport chain, by 12–15 percent in trained cyclists. Similar adaptations likely occur in swimmers, allowing them to produce ATP more efficiently at high intensities.

Individual Variation and the “Responder” Phenomenon

Not every athlete responds equally to altitude. Genetic factors, baseline hematocrit, iron status, and training history all influence the magnitude of adaptation. Smith appears to be a “high responder” – her hemoglobin mass has increased by approximately 6–7 percent over multiple altitude camps, according to unpublished team monitoring data. This is at the upper end of the typical response range. Coaches monitor her ferritin levels closely because iron is required for both hemoglobin synthesis and mitochondrial function. When ferritin dips below 40 ng/mL, Smith takes supplemental iron to prevent blunted adaptation.

This individualized approach is critical. Altitude training without careful bio‑monitoring can lead to overtraining, increased injury risk, and even performance decrements if the athlete returns to sea level too soon before competition. In Smith’s program, she typically returns to sea level 10–14 days before a major meet, allowing her body to “unload” the extra red blood cells while still retaining the benefits of improved oxygen delivery.

Altitude Beyond the Blood: Psychological and Tactical Benefits

The physiological advantages are well documented, but altitude training also offers less tangible benefits that can be equally important. For Smith, training at altitude forces her to focus on pacing and technical efficiency. When the oxygen is thin, every wasted movement is magnified. Swimmers learn to reduce drag, improve body position, and fine‑tune stroke mechanics because at altitude they simply cannot sustain a sub‑optimal technique.

“At altitude, you have to be incredibly deliberate about your technique from the very first lap of practice,” Smith explained in a 2024 interview. “When you come back down to sea level, those good habits stick, and you have more oxygen to work with. It feels like a cheat code.” This sentiment is echoed by many elite middle‑distance swimmers who use altitude camps as a forced technical reset.

There is also a psychological resilience built through difficult training environments. Completing a hard set in Flagstaff, where the air is dry and the sun is intense, builds confidence that carries over into competition. Smith’s ability to close fast in the final 50 meters of her 200‑meter backstroke in 2024 can be traced in part to the mental toughness cultivated during those altitude sessions.

Limitations, Risks, and Ethical Considerations

Altitude training is not a panacea. Excessive time at high elevation can lead to acute mountain sickness (AMS), characterized by headache, nausea, and poor sleep. Long‑term stays without adequate nutritional support can cause iron deficiency, weight loss, and increased susceptibility to infections. For swimmers, the dry air at altitude also exacerbates respiratory irritation, and many athletes report a higher incidence of asthma‑like symptoms during altitude camps.

Furthermore, the benefits of altitude training are temporary. Once an athlete returns to sea level, the elevated red blood cell mass begins to decline after about two weeks. The optimal “window” for competition is narrow — typically between days 3 and 14 after descent. Missing that window can leave an athlete feeling flat or overly fatigued. Smith’s coaching staff uses precise timing based on her individual desaturation rates and training load to schedule her trips to major meets like the World Championships and Olympic Trials.

Ethically, altitude training occupies a clean space in sport, unlike blood doping or EPO administration, because it uses natural environmental stress. However, some critics argue that access to altitude training is unequal — not all athletes have the resources to travel to high‑elevation centers or to purchase altitude tents. Smith benefits from being part of a well‑funded national team program and a top collegiate system, which raises questions about fairness even within the boundaries of legal preparation. Governing bodies like World Aquatics and the U.S. Anti‑Doping Agency do not restrict altitude training, but they monitor hematological profiles to detect any blood‑doping that might mimic altitude adaptation.

Integrating Altitude into a Modern Training Program

Regan Smith’s success is not the result of altitude alone. Her training program incorporates high‑volume aerobic work (up to 80,000 meters per week in base phases), specialized dry‑land strength work, and a heavy emphasis on underwater kicking. Altitude serves as a booster that amplifies the effects of all other training. Coaches typically schedule two to three altitude camps per year, each lasting three to four weeks, with the last camp ending approximately 10–12 days before the season’s major meet.

“Altitude is not a shortcut, it’s a magnifier,” said a U.S. national team coach who worked with Smith in 2023. “If the base isn’t already strong, altitude will just make you tired faster. Regan’s work ethic and her aerobic foundation are what make the altitude response possible.”

Technology plays a supporting role: Smith uses a pulse oximeter to track her overnight oxygen saturation, and her coaches adjust her training load based on trends in resting heart rate and HRV. Altitude tents are used for six to eight hours per night during the two weeks immediately before and after camps to extend the hypoxic stimulus. This hybrid approach maximizes the hematological adaptation while allowing her to train at full speed during the day.

Looking Ahead: The Future of Altitude Training for Swimmers

As researchers continue to unravel the genetics of individual response, altitude training will become increasingly personalized. Some swimmers may benefit more from “normobaric hypoxia” (simulated altitude via tents or rooms) than from actual high‑elevation camps, which come with travel and time‑zone complications. Others may respond best to “intermittent hypoxic training” – short, high‑intensity intervals performed in low‑oxygen environments to stimulate local muscle adaptation without the systemic hematological shift.

Regan Smith’s trajectory suggests that when altitude is integrated thoughtfully, it can help an already elite athlete continue to improve even beyond expected age‑related gains. Her best times in 2023 and 2024 are approaching – and in some cases surpassing – her world‑record performances from five years earlier. For swimmers and coaches looking for a competitive edge, Smith’s story offers a blueprint: start with a solid base, measure everything, and respect the body’s need for time at sea level to realize the full benefit of altitude.

The effect of altitude training on Regan Smith is not an anecdotal blip but a case study in how modern sports science, when applied with discipline and individualized monitoring, can produce measurable, repeatable performance gains. For any athlete willing to put in the work at high elevation, the air might be thin, but the potential is anything but.

For more information on altitude training protocols, see the U.S. Olympic & Paralympic Committee’s altitude resources and a review of recent research published in Medicine & Science in Sports & Exercise. Regan Smith’s official athlete page is available at USA Swimming.