Disclaimer – Important
Heat adaptation training should be done in collaboration with and experienced coach or trainer and with prior medical clearance. Heat illness is a very real and dangerous thing, so work with a professional. If during any session you don’t feel good, just stop and cool down.
Training for Heat Adaptation?
There was a lot of discussion about heat acclimation and heat adaptation in the build-up to the Tokyo Olympics. Everyone seemingly having their own protocols and strategies, but also keeping things fairly close to their chest.
There is no one way to do it, and like many other types of training you need to find what works for the individual. This can come down to what facilities or equipment you have available to you. Or it could be the individual preference of the athlete.
Initially, it can be split into 2 broad categories, Passive and Active:
Within that, the strategies that have been used and tested are extremely varied. There doesn’t seem to be that many studies where the same strategy has been used repeatedly! Everyone has their own ideas. From a practical point of view, you need to find your ‘heat training zone’ and for that the only experience I have is by using the Core Sensor. Finding the zone using their heat ramp test.
As above, there are passive and active strategies to raise the core temperature. Passive strategies are commonly used post training, gradually increasing the time in the passive heat environment.
Trying to cut through to heart of the issue, it seems that the common threads are that a block of heat sessions is complete within a 5–14-day period, however, some studies using passive strategies have lasted longer. Like all fitness gains, they are reversible, so the heat block is followed by a period of maintenance sessions to keep the gains. Research using 2-3 maintenance sessions per week has been shown to be a very successful process. The adaptations can be maintained with a 60-90 minute heat session every 2-4 days.
Looking at the physiology of the gains, the vast majority of the gains are made within the first 5-7 days. After that there are still gains to be made, but that has to be balanced with the impact on other training goals and sessions. Because, make no mistake, these sessions will be relatively low power/low pace (especially at first), but they are not easy sessions. They take their toll and so need to be respected with appropriate recovery and are possibly at the expense of other types of developmental sessions.
There have been lots of variations tried to minimise the impact on the training programme as a whole. For example, using heat chamber or heat bath to increase core temperature after a regular training session. Or alternatively, at the end of an indoor training session, turning off the fans or putting on extra clothes to increase core temperature for a 30 minute heat training session. However, this still has a cost and you can’t just train fully as normal + heat training and expect it to have no impact. You have to respect the cost of all types of training and balance it. When you first start out, I would be particularly cautious until you find out how you react and how quickly you recover. It’s very individual, and like all training types, there is a learning curve.
Heat Adaptation and Performance Gains
The primary reason so much research has been conducted into heat adaptation is because of the massive decrease in endurance performance seen in the heat. The research certainly indicates that heat adaptation mitigates some of these decreases in performance. However, some of the continued interest in heat training has come from the increases in endurance performance that occur regardless of whether the event is in the heat or not.
To look at the mechanisms that underpin performance, a good place to start is the Fick Equation. This is the equation explains the make up of VO2max…see below:
Changes in VO2max (whether up or down) require a change in part of this equation. Now not all elements of the Fick equation can be changed equally. I apologies, as I can’t remember where I took the notes from that led to me drawing this table in my notebook, but I believe it was either a Stephen Seiler podcast or YouTube video.
However, it has proved very useful to me and my understanding of endurance physiology. The table below breaks down the elements of the Fick equation into its components and divides them into the ones that are more or less trainable.
Looking Deeper at the Research
Heat training will most certainly have an influence on some of the elements of the Fick equation. The primary mechanism for this is through plasma volume expansion. As we have discussed, increased plasma volume is one of the known effects of heat training. Some interesting research in the 80’s and 90’s looked at the effects of changes in plasma volume.
In 1986, Coyle, et al. concluded that the decrease in VO2max of well-trained endurance athletes, after 2-4 weeks of detraining, was caused by the loss in plasma volume. The mechanism behind the decreased VO2max is potentially the lower stroke volume, higher relative heart rate and increase in total peripheral resistance that was found when the athletes were in the detrained state. The genius of this study lies in what they did next. After the re-test, they infused the lost plasma and re-tested the athletes. Even in the detrained state, the measures of cardiovascular function all returned to near normal levels. Though in this study, measures of performance were not used, they were used in a follow-up study in 1990. The set-up of this study was a little different, in that they didn’t do the detraining, but instead infused different amounts of fluids to expand plasma volume and then looked at performance changes and cardiovascular function. They found that there was a balance to be had between increasing plasma volume and the reduced haemoglobin concentration. They found that a moderate increases in plasma volume of around 300ml increased stroke volume by 10-15% with only a 4-5% decrease in haemoglobin concentration.
In the group who received these larger increases in plasma volume (480ml) diluted the haemoglobin concentration by 11%, but with no further increase in stroke volume.
The reason the stroke volume increase is important and has potential performance advantage is due to the Frank-Starling Law. The Frank-Starling Law describes the relationship between the stretch of a muscle fibre and the resultant force the fibre produces. Specifically, the more a fibre is stretched the more force it is able to produce in the subsequent contraction. This is as true for cardiac muscle as for any other. The greater plasma volume causes increased stretch from the greater filling, and therefore a more forceful contraction.
So…Does Heat Adaptation Improve Performance?
The most important thing about these outcomes is the impact on performance. And in this study the VO2max and performance at VO2max increased in the group with a moderate 300ml plasma expansion, whereas there was no improvement with the larger plasma expansion group.
Bringing it back to heat training, a study by Keiser, et al. (2015) found an average increase of 200ml in plasma volume following a 10-day heat training protocol. This also resulted in a significant increase in V02max (9.6%) and in time trial performance (10.4%).
It is thought that if plasma volume remains elevated for extended periods that the haemoglobin concentration will normalise to the same percentage of blood volume, which means a double bonus, as the plasma volume will be expanded without dilution of haemoglobin. A study in 2020, by Ronnestad, et al. investigated this in elite cyclists and found an increase of 42 grams of haemoglobin after 5 weeks of heat training. They concluded that heat training can increase haemoglobin mass with a small to intermediate effect on cycling performance parameters. Which is what it’s all about in the end! Other recent studies have looked at endurance performance outcomes following heat training. For example, in 2021 Maunder, et al. found significantly greater performance increase in athletes who had done 3 weeks of heat training when compared to the same training programme carried out in moderate temperatures.
Summary
In the last two posts we’ve looked at heat adaptation training from all angles and hopefully shown you how it may be beneficial to performance, and particularly to performance in a hot environment.
We’ve looked at how performance in the heat is reduced due to the bodies increasingly tricky task of removing heat from the body, how heat training can be carried out and what adaptation your body will make to improve performance in the heat.
We’ve also explored the physiological principles that underpin the use of heat training and their adaptations.
I have written about my personal experiences during a heat block, which you can see here:
Heat Training Block – Case Study – Part 1
If you have any further questions, you are welcome to get in touch at: coach@summitcyclecoaching.co.uk
References
Coyle, E.F., Hemmert, M.K. and Coggan, A.R., 1986. Effects of detraining on cardiovascular responses to exercise: role of blood volume. Journal of Applied Physiology, 60(1), pp.95-99.
Coyle, E.F., Hopper, M.K. and Coggan, A.R., 1990. Maximal oxygen uptake relative to plasma volume expansion. International journal of sports medicine, 11(02), pp.116-119.
Keiser, S., Flück, D., Hüppin, F., Stravs, A., Hilty, M.P. and Lundby, C., 2015. Heat training increases exercise capacity in hot but not in temperate conditions: a mechanistic counter-balanced cross-over study. American Journal of Physiology-Heart and Circulatory Physiology, 309(5), pp.H750-H761.
Maunder, E., Plews, D.J., Merien, F. and Kilding, A.E., 2021. Stability of heart rate at physiological thresholds between temperate and heat stress environments in endurance-trained males. International Journal of Sports Physiology and Performance, 16(8), pp.1204-1207.
Rønnestad, B.R., Hamarsland, H., Hansen, J., Holen, E., Montero, D., Whist, J.E. and Lundby, C., 2021. Five weeks of heat training increases haemoglobin mass in elite cyclists. Experimental Physiology, 106(1), pp.316-327.