Start the Season with Heat Training

Not only for hot races

Heat training boosts performance not only during hot races. Long-term heat training increases red blood cells, improving power at lactate threshold. This explains why many of the world’s top athletes start heat training very early in the year and continue it throughout the season.

The season’s start can be a particularly convenient time for several weeks of a heat training block. Both low-intensity workouts and indoor training in a controlled environment are conducive to a heat block. Afterwards, the haemoglobin and performance gains will be present by the time more intense training occurs. Maintaining those gains is much easier to fit into a regular training schedule.

The latest research

The latest research continues to support the benefits of long-term heat training. In November 2002, the Scandinavian Journal of Medicine & Science in Sport published “High or hot – Perspectives on altitude camps and heat-acclimation training as preparation for prolonged stage races”. It reviewed existing research to provide practical guidance for elite cyclists.

One key finding was the ease of maintaining the performance gains achieved through heat training. The haemoglobin gains of heat training can be maintained indefinitely through several days/week of “maintenance” heat training.

In contrast, the red blood cell gains from 3–4 weeks of altitude acclimatisation are lost very quickly – half disappear within 7 days of return to normal altitude, and all gains are lost within 14 days.1

Immediate and extended gains

After beginning a heat-training block, physiological changes happen in two stages, providing both immediate gains and gains achieved over an extended time.

The immediate gains begin within a couple of days and plateau within 7–14 days. These changes increase blood plasma and enhance sweat gland functions. This boosts the maximal sweat rate, lowers the resting core temperature, and lowers the temperature threshold for the onset of sweating.1 These adaptions are ideal for training and racing in a hot climate, as they largely prevent the power losses typically associated with the heat.

The extended gains primarily increase red blood cell volume and take full effect after 2–4 weeks of heat-block training. This change has been shown to boost VO2max, power at lactate threshold, and time trial performance by 5–8% in both hot and cool conditions2.

Getting started with heat training

A heat training block takes 2–4 weeks and involves 6–7 heat training workouts/week. During each of those workouts, the athletes should spend 45–60 minutes in his/her personalised heat training zone (some of that time can be accumulated post-workout in a hot bath or sauna). More details can be found in the article Heat Training for Sporting Performance.

Less-frequent and shorter-duration exposure will still induce red blood cell gains, although adaptions will take longer. The “High or hot” article referenced above used 5 heat workouts per week and found that after a 5 week study, full red blood cell gains had been made (unfortunately, no analyses were done before the end of the 5 weeks).

CORE has also outlined simple heat training plans for triathletes, cyclists and runners. These require only 3 heat sessions per week that are easily blended with normal training at any time of year. While the building of haemoglobin will take longer at this frequency, many athletes find the routine very convenient.

Maintenance of haemoglobin gains

Maintaining haemoglobin gains is simple. It only requires 2–3 heat sessions per week, in each session spending 45–60 minutes in the heat training zone. As in the heat block, portions of this “time in zone” can be accumulated post-workout in the sauna or hot bath. With such a maintenance plan, haemoglobin gains can be maintained indefinitely.

If exposure to heat is interrupted for a significant period, the body will lose the adaptions made through heat training. Resuming heat training will re-establish those plasma and red blood cell gains.


  1. Nybo, L, Rønnestad, B, Lundby, C. High or hot—Perspectives on altitude camps and heat-acclimation training as preparation for prolonged stage races. Scand J Med Sci Sports. 2022; 00: 1-10.
  2. Lorenzo S, Halliwill JR, Sawka MN, Minson CT. Heat acclimation improves exercise performance. J Appl Physiol (1985). 2010 Oct;109(4):1140-7. doi: 10.1152/japplphysiol.00495.2010. Epub 2010 Aug 19. PMID: 20724560; PMCID: PMC2963322.