Heat is often debilitating for a runner. Heat cramp, heat exhaustion, dehydration, heat stroke, headaches and the desire just to stop are all very real problems.

As the summer season approaches, running in a hot climate is sometimes unavoidable, however, racing in a hot climate is relatively controllable as you will understand in advance the race, the environment and the expected temperatures one can expect.

Understanding the conditions of ones running and racing environment is crucial to make the best of all the hard training you have done. So, one needs to adapt and plan.

Heat acclimatisation takes place in a natural environment where one can specifically prepare in advance of a chosen race or project, ideally for 7-14 days before the event. For most of us though, the luxury of travelling for 14-days and having an acclimatisation holiday is not a realistic proposition.

This is where Heat Acclimation comes in. In simple terms, this is about providing heat stress in a controlled environment, typically a heat chamber, over a set period of time and sessions.

Dr Jodie Moss has specialised in heat acclimation and in the process, put her learning to real time use at the 2019 Marathon des Sables where she placed 8^th woman.

With Marathon des Sables approaching, it is timely to re-visit and gain a full understanding of what is required to acclimate to heat with an interview with Dr Jodie from July 2020.

Podcast HERE.

What is it about heat that makes running so difficult?

You are imposed upon by a different challenge. What happens is you create this metabolic heat by contracting your muscles. When one runs, you use muscle mass and this generates heat. When you then exercise in a hot environment, particularly if it is greater than skin temperature, then this makes it very difficult to get rid of heat. Humans are not the most efficient mechanically, so this energy from contracting muscles, potentially around 20 to 30% of the mechanical energy being made is converted to chemical energy, that means 70%, maybe even more, needs to be eradicated in the environment. If the environment is hot, for example, the Sahara, a challenge is imposed to eradicate the heat and what often happens is is that the heat is stored and one feels hotter and this then has a cascade effect of issues and problems, physiologically and perceptually.

Physiologically:

An increase in skin temperature is likely the one which is noticed first as it is directly impacted upon by the environment. There will be an increased demand for blood flow that needs to go to muscle to provide it with oxygen/ energy to run, but also there is a competition for blood flow to the skin. In order to thermo regulate, blood is competing with muscles and skin and that creates an impact on one’s cardiovascular system. Typically, heart rate will increase due to the increased workload sending blood to muscles and skin.

Body core temperature will increase.

Sweet rate will also increase and therefore the percentage of water loss will increase and the consequence of this is dehydration – a deficit in body water with onward complications.

Perceptually:

We thermally perceive it to be a lot hotter.

You are more uncomfortable.

The feeling of needing to slow down and therefore performance is impacted.

Is heat acclimation as valid for the runner at the front, as well as the runner at the back?

In principal, yes. However, if we take Marathon des Sables as an example and the winner, Rachid El Morabity, he is a Moroccan, he lives in the environment in which the race takes place, therefore he is naturally acclimatising on all his training runs. Therefore, he has no need to acclimate artificially.

Highly trained individuals though, through training, can gain thermal adaptations, irrespective of environment. For example, if you are training everyday, particularly at a high percentage of VO2max, one will create heat this will require a higher sweat rate and therefore adaptation takes place. But, interventions should be in place both acute and chronic, to minimise the effect of environment on performance. Environment, will always have an impact on performance, no matter which athlete.

When is a good time to start adapting to heat and how?

It is a consideration for close to competition, typically in a period of 7 to 21-days. Adaptation from exposure diminishes rapidly, so, there is no need to do this too far away from the chosen event. 

Now of course, if one is fortunate with time, the best scenario is to travel to the race location and adapt naturally in the environment of the race. However, very few have such a luxury and this is where acclimating as opposed to acclimatising steps in.

However, budget can be an issue, so it is possible to adapt via some simple home methods. Keep one’s training as planned, say by a coach, and then add layers of clothing while training. Have a hot bath after training. One can also consider Bikram Yoga and say saunas. But, and this is a big but, while some of these interventions will have some benefit, it is not something that can be recommended completely as it is harder to prescribe and measure.

We want heat adaptation and these adaptations only occur when there is sufficient thermal strain.

As an example, one could run for an hour with layers and build heat. Then immediately have a hot bath. Water has a greater density than air and the heat inside the body would be retained and most likely increase, this would stress the system. But, the issues arise with how long does one do this… Ultimately though, this is considerably better than nothing!

By far the best way, is environmental heat chamber.

Environmental Heat Chamber

The jury is still out on what is the optimal sessions for performance gain, however, five sessions would be considered fundamental over a period of 7 to 14-days. This period has shown results of a much more fulfilled adaptation. The pseudo motor function (sweat rate) takes a little longer to occur, but all the other measurements, cardiovascular and lowering core body temp occurs quite rapidly. So, based on sweat rate, a longer period of time provides the best results.

 In regard to the sessions, they could be performed every 2-days, every other day, every day and some even do 2 sessions per day. But obviously time and budget is a huge factor.

It is also important to remember that these sessions take place close to competition, so, monitoring stress and recovery is equally important. 

In regard to session length, 60-minutes is usually adequate and this allows the body to get hot enough.

I get asked about adding a run pack and weight, for example, MDS is a self-sufficient race and a pack is required. On the start line, the minimum weight will be 8kg. But training with this in the heat is not necessary, but some insist as it provides security, comfort and a greater understanding of what the Sahara, as an example, may feel like. But this adds additional stress and the sessions are about heat adaptation.

The Protocol

Isothermic heat acclimation intervention is typical. We get you to exercise so that your core reaches a certain temperature. For this we use a rectal thermistor. This ensures that you meet the thermal stimulus, crucial for sessions like this.  

We measure body weight naked and this allows us to monitor fluid intake and sweat rate. We can test urine to look at hydration status too. This is all about making the client aware of hydration and levels. We also want the client to leave a session re-hydrated!

A treadmill or bicycle is used. Personally, I prefer the bike as it adds less impact to the body. It’s important to remember, these sessions are about heat adaptation, they are not training sessions. A 5-minute check will include hear rate, core temperature, skin temperature, perception of thermal environment, how hot does the client think it is? And finally, I will ask how comfortable the client is. Then, the exercise will begin.

We aim for a core of 38.5 degrees in each session. This is ideal for pseudo motor and thermo functions to be maximised. It ensures that we are always controlling and meeting a fixed criteria. Measuring the thermal strain is key. It usually takes about 30-minutes to get to 38.5 degrees depending on the individual. But external factors do have an impact. 

We typically see improvements by session 3. But it is important to have, say 10-minutes of each session fixed, that way we can monitor improvement and adaptation. We can gain the data here and then report back. Day 5 to day 7 will show the most improvement. So, 7-sessions.

Time can be an issue and some may prefer to squeeze two sessions per day and compress 7-days, say, into 3 or 4. This is possible and literature confirms this. Total exposure is more important than days.

Ideally, the last session would be 1 or 2-days before departure for the chosen race.

What problems can occur without acclimation and how does one mitigate it?

A runner will be faced with a physical and perceptual challenge that will have negative effects. They will be slower, frustrated, dehydrated and have a potential of heat stroke and ultimately they may not finish the race. If any of these elements are experienced, try to cool as much as possible, seek shade at aid stations, rest and allow the core to lower. Hydrate and use spare water to provide a perceptual cooling. Water on face, head, forearms and neck will help a little.  

On a personal note:

I did not have the perfect race and that is what makes me keep signing up to race. My heat protocols were great but I compromised my training and I was surprised with 8^th place. I had an amazing support system and I do have chronic heat exposure, I am also very good at getting rid of heat. I also sweat high. But I need to be careful on dehydration. I made a mistake with my pack trying to make it as light as possible but I compromised my pack integrity and this hurt my back. I look forward to going back, I hope in 2021.

Top 3 tips to get ready in regard to heat and training.

1. Have a heat protocol as outlined above.

2. Test all kit and nutrition, leave nothing to chance.

3. Do not panic. Trust the training you have done. Do not increase mileage and training in the light stages. Do not risk injury or illness. Be healthy.

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