Endurance: hot baths to run faster?

Training at altitude: a practice inaccessible to most people

For elite runners, going on training in the mountains to improve their performance is a well-known practice. Indeed, at high altitude, the lack of oxygen pushes the body to produce more red blood cells, thus increasing its capacity to transport oxygen. Back at sea level, this adaptation results in better endurance performance.

In The science of competition-specific enduranceFred Belaubre, professional triathlete and five-time European champion, testifies: “Since the start of my triathlete career, at 16, I have participated every year in several altitude courses, in Alpe-d’Huez and Font-Romeu, one in January and one in the spring, before the start of the season. In Olympic years, I did one more internship at the beginning of spring. »

But this type of preparation is often inaccessible to amateur athletes, as explained by Mike Stembridge and Elliott Jenkins, from Cardiff Metropolitan University, in an article published on the site The Conversation (1): “Training at altitude requires time, financial investment and long-distance travel. For the vast majority of runners, this simply isn’t an option. » That’s why they looked for an alternative, turning to another environmental stress: heat.

The protocol: a bathtub and a thermometer

For their experiment, they asked 10 well-trained runners (including 9 men) to continue their usual program, with just one addition: simple hot baths (2). “The baths were not high-tech laboratory equipment. They were ordinary bathtubs. The water temperature was maintained at 40°C using an inexpensive thermometer, with hot water added if necessary. Each session lasted 45 minutes and was carried out shortly after training. »

How heat affects the blood and the heart

The mechanism is not exactly the same as that of altitude, but its final result is close. A single heat session has the effect of increasing the volume of plasma, the liquid part of the blood. The red blood cells are therefore transiently more diluted, which temporarily lowers the oxygen concentration. The body responds by producing more red blood cells to restore balance. Ultimately, the entire blood volume increases.

The researchers also observed cardiac changes: the left ventricle of the heart, already hypertrophied by endurance training, further increased in volume after the five weeks of bathing. “The extra blood created by heat exposure likely contributed to this expansion.” Together, these changes improved aerobic capacity. »

+4% VO₂max without increasing training

On average, runners’ VO₂max increased by about 4%, and they were able to reach higher maximum speeds in treadmill tests. “Improvements of this magnitude are significant for trained athletes, especially since these gains were achieved without increasing training intensity or mileage,” underline the two authors.

The advantage of this approach also lies in the fact that it is low risk. Increasing mileage or training intensity puts runners at risk of injury. Hot baths, on the other hand, work the cardiovascular system without placing additional stress on the muscles and joints.

Read: Ironman des Sables d’Olonne: how I beat my record

An affordable strategy but with precautions to take

Unlike high altitude courses, most people have access to a bathtub. The researchers emphasize this dimension: “This opens up the possibility of more equitable access to (fully legal) performance-enhancing strategies for as many runners as possible.” »

Like all research, this study has limitations. The protocol involved water at 40°C, 45 minutes per session, five times a week for five weeks. It’s unclear whether shorter sessions, lower temperatures, or other heat sources like saunas would produce the same effects.

The authors also point out that their measurements focused on physiological markers and performance on the treadmill, not on running times. Longer term studies will be needed to confirm these results in real competition.

Finally, precautions are necessary in terms of security. Prolonged exposure to heat can cause dehydration, dizziness or heat stroke. Anyone wishing to try this protocol should hydrate properly and people with health problems should consult a doctor.

The protocol in practice

Water temperature: 40°C
Duration per session: 45 minutes
Frequency: 5 times a week, just after training
Length of period: 5 weeks

To go further: The science of competition-specific endurance