Heat Training Maintains Hemoglobin Gains Following Altitude Training

Numerous controlled studies have shown that extended, systematic heat training can increase hemoglobin mass. Studies have also shown that once those gains have been made, they can be maintained with reduced heat exposure.

Now, a study has shown that the hemoglobin mass gains achieved during altitude training can also be maintained through heat training. This has major real-world implications. Currently, most athletes descend from altitude 7–18 days before a sea-level race. The narrow window for competition is because of the rapid decay of hemoglobin and performance gains that occur at sea level.

However, the study Heat Suit Training Preserves the Increased Hemoglobin Mass Following Altitude Camp in Elite Cyclists found that heat training preserved altitude-induced hemoglobin gains for at least 3.5 weeks after returning from altitude.

Study summary

18 elite male cyclists first undertook a 3-week altitude camp. On average, they gained 4.1% of hemoglobin mass and reduced plasma volume by 8%. Then, they returned to sea level and were split into two groups (heat and control). Each group performed the same training, aside from each week the heat group replaced 150 minutes of low-intensity training with 3 heat sessions of 50 minutes each.

After 3.5 weeks of sea-level training, the control group had lost 71% of the hemoglobin mass it had accrued at altitude. In contrast, the heat group had maintained all of its hemoglobin mass gains.

Heat maintenance

CORE staff tested the heat maintenance protocol used in the study. We believe that the study athletes likely incurred a Heat Training Load of approximately 4 during each of their 50-minute sessions, totaling approximately 12 for the week. The study's maintenance protocol appears similar to the heat maintenance schedule that CORE recommends (2 sessions/week with a Heat Training Load of 6 each time, or 3 sessions/week with a Heat Training Load of 3.5 each time).

Real-world implications

CORE was of course excited by these findings, and we were curious about some of the real-world implications for training and racing. The leader of the study, Daniele Cardinale, graciously offered to answer some questions that extend beyond the findings of the study. Daniele is researcher at the Department of Physiology, Nutrition and Biomechanics at The Swedish School of Sport and Health Sciences GIH and Performance developer officer at the department of Elite Sport Support at The Swedish Sports Confederation. As a coach himself, he is very familiar with applying research results to athlete protocols.

Your study monitored hemoglobin mass 3.5 weeks after leaving altitude. Do you believe that continued heat training can sustain those gains for longer – perhaps 8 or 12 weeks?

Yes, I believe that by extending the heat exposure period, hemoglobin mass could be maintained for a longer period than 3.5 weeks. However, as with all stressors, heat would need to be modulated to keep its effectiveness.

It’s our understanding that blood plasma volume decreases at altitude and takes some time to recover to a baseline volume after returning to sea level. If athletes compete in a hot climate too soon after returning from altitude, are they less heat adapted because of lower plasma volume?

I would not recommend competing in a hot climate shortly after an altitude camp without a proper heat acclimatization phase beforehand. Heat acclimatization is multifaceted and involves more than just an increase in plasma volume. However, in our study, during the 3.5 weeks at sea level the HEAT group displayed a numerically larger increase in plasma volume from post-altitude than the control group (12% vs. 6%, respectively). Therefore, it could be speculated that the larger increase in blood volume following HEAT during the 3.5-week maintenance period could be beneficial for the athlete by increasing the stroke volume and thus, the maximal cardiac output, via the Frank-Starling mechanism – as well as better thermoregulation during prolonged exercise.

There are only a few controlled studies that simultaneously combined altitude and heat training. Do you have a sense for what type of protocol might make for an effective combination of the two? And what might be the benefits of that approach?

The combination of altitude and heat training is an extremely interesting and largely unexplored area, and I’m currently researching it. Stay tuned!