What Actually Happens to the Body with an Altitude Camp?

Dr Stephen Cheung undertook an 18-day altitude training camp in Flagstaff, Arizona, to investigate the physiological and performance effects of living and exercising at moderate altitude. Flagstaff, situated at 2,100 metres, offers an ideal environment for altitude training without the crowds typical of more famous locations like Boulder. Although not a professional athlete, Cheung used this opportunity to conduct detailed blood tests and track his trail running performance, providing rare insight into how altitude exposure affects the body. The primary focus of the physiological testing was on total haemoglobin mass (tHb), measured through a carbon monoxide rebreathing technique regarded as the gold standard for quantifying haemoglobin. Initial results showed Cheung’s tHb was already above average for endurance athletes, suggesting a strong baseline. Other markers, such as haematocrit and ferritin levels, fluctuated during the camp, reflecting typical dehydration effects on arrival and iron metabolism changes, but overall his haemoglobin mass slightly decreased by the end of the stay. Despite the lack of haemoglobin increase, Cheung’s running performance improved markedly over the course of the camp. His times on a challenging uphill Strava segment steadily dropped by around 15 seconds every few days, culminating in what he described as possibly the best run of his life. This improvement occurred without the expected physiological adaptation in haemoglobin mass, indicating other mechanisms—such as enhanced muscle efficiency or oxygen utilisation—may contribute significantly to altitude training benefits. Cheung’s findings challenge the conventional wisdom that haemoglobin mass increase is the primary driver of altitude training gains, especially for athletes who already have a high baseline. The study underscores the complexity of altitude adaptation and suggests that performance improvements can occur through multiple pathways. For athletes and coaches, this highlights the importance of personalised approaches to altitude camps and the potential value of monitoring a range of physiological and performance metrics beyond haemoglobin alone.