The benefits of altitude training have been well understood for many years. The current school of thought is that to optimise the effectiveness of altitude training, athletes should aim to train at lower altitudes and spend the rest of their time at a higher altitude, which drives adaptations such as increased haemoglobin.
However, the gains from altitude training are short-lived. Once an athlete returns to sea level, the adaptations begin to fade, just as the biggest mountain stages of a Grand Tour begin. As a result, riders could find themselves almost back to square one just when the altitude training is needed most.
A recent study, though, has investigated the role that heat training, post-altitude camp, can have on the prolonged benefits of altitude training. The findings suggest that even moderate amounts of heat training after an altitude camp could be a key strategy for keeping those hard-won physiological gains.
A highly relevant sample, but small enough to raise doubts
The study, done in 2024 and published in January in the journal Medicine & Science in Sports & Exercise, is from a noted group of experts in altitude and heat training, including Bent Rønnestad and Joar Hansen of Inland Norway University of Applied Sciences and Daniele Cardinale of the Swedish School of Sport and Health Sciences. (Both, you might recall, have also investigated carbon monoxide rebreathing, in part as a tool to track changes in haemoglobin mass during altitude training; that method was also used in this study.)
The current study explored whether heat suit training preserves the increased haemoglobin mass following an altitude camp. It used a small dataset of highly trained elite riders with just 18 male professional athletes making up the full study group. While the participants had highly relevant physiology, the small sample size limits broader conclusions.
Typically, small sample sizes reduce statistical power, making it harder to detect real effects with much certainty. Yet this study reports very low P-values, which usually implies strong confidence in the results. This mismatch does raise eyebrows, as we will discuss later.
All 18 riders took part in the same three-week altitude training camp at 2,100 metres above sea level. Once this block was complete and the riders returned to lower altitudes, half of the test group continued training as normal. The other half swapped some of their low-intensity volume for three 50-minute heat sessions per week. The goal: raise core temperature to 38.5 °C (101.3 ºF) and provoke ~1.8 litres of sweat loss using heat suits.
To monitor the differences between the control and the heat training groups, all riders had their haemoglobin mass (Hbmass) and blood volume assessed with a short session of CO rebreathing before, two days after, and 3.5 weeks after the altitude camp. In both groups, the study found an average 4.1% increase in Hbmass at the end of the camp. That's expected; it's what happened next that is interesting.
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