In the weeks leading up to the Tour de France, many of the race’s top cyclists gather each May in Sierra Nevada, Spain, to undergo altitude training aimed at enhancing their performance for the prestigious event. The remote mountain resort, situated over 7,600 feet (2,300 meters) above sea level, offers a unique environment where elite riders can acclimate to thinner air and boost their endurance ahead of the July race.

Sierra Nevada’s Centro de Alto Rendimiento, or Center of High Performance, hosts a range of facilities including Europe’s highest soccer field, an athletics track, and an Olympic-size swimming pool, serving as a training hub for visiting cyclists who share the slopes and streets of the quiet ski town. During this period, the usually bustling winter resort is nearly deserted, providing a stark contrast to the fervent atmosphere of races.

Cyclists such as Tadej Pogacar of Slovenia, Juan Ayuso of Spain, and Remco Evenepoel of Belgium spend multiple weeks at altitude camps to gain physiological advantages. These include increased production of red blood cells and erythropoietin, a hormone that stimulates oxygen transport in the blood, allowing for improved stamina and exertion during long and demanding stages of the Tour. The practice of altitude training dates back to the 1968 Mexico City Olympics, when athletes who prepared in high-altitude conditions saw significant performance improvements.

“It’s very difficult to perform well in a Grand Tour without doing an altitude camp,” said Spanish rider Carlos Verona, who will support Ayuso during this year’s Tour. He noted that altitude preparation has shifted from being a supplementary activity to an essential component of modern cycling training.

Riders follow rigorous daily routines, including lengthy rides from Sierra Nevada down to Granada and back, interspersed with interval tests and careful physiological monitoring. Coaches and medical staff track multiple metrics—such as heart rate variability, oxygen saturation, and lactate levels—to optimize training loads and ensure adaptation to the demanding environment.

Despite the benefits, the initial days at altitude can be challenging. Czech cyclist Mathias Vacek described the first two days as physically taxing, with everyday efforts feeling twice as difficult. Off the bike, riders seek distractions to alleviate the isolation, often passing time with activities such as gaming or model airplane flying, and occasionally engaging in informal competitions.

Training at altitude also requires attention to health risks unique to the setting. For example, Ayuso experienced a bee sting during one training session, prompting medical staff to limit his activity to prevent additional physiological stress on top of the already taxing high-altitude conditions.

The meticulous preparation undertaken at Sierra Nevada exemplifies the high stakes and scientific approach intrinsic to elite cycling. Coaches emphasize that neglecting altitude training would put their riders at a substantial disadvantage, as most competitors include it in their regimens.

As the Tour de France begins with its opening stages, the intense days spent in the sparse mountain air of Sierra Nevada will manifest in the riders’ endurance and performance on the road, underscoring the pivotal role that this hidden training ground plays in shaping the world’s top cycling event.