Heat can be an ally for some athletes and an enemy for others. We can see riders excel when the mercury rises and temperatures soar over 30ºC (86ºF), while others surprisingly fade from the peloton.

How can individuals who typically struggle (or have little experience) in the heat adapt their training to cope with hotter race conditions?

In a special guest blog, cycling coach Aitor Altuna lifts the lid on his approach to helping you individualise your training in the heat...

The effects of heat during exercise

When cycling in the heat, the human body is simply unable to exercise as hard as in temperate conditions, although the process of heat training can go a long way to enable performance in all conditions.

During exercise, humans are about as efficient as the combustion engine in your car. This means that around 75-80% of the energy burned during exercise is released as heat energy. At rest in temperate conditions, most of your heat produced via metabolism can usually be lost via non-sweat mechanisms (e.g., radiation, conduction, and convection). As soon as we start exercising, however, as the mercury rises and reduces heat loss via those non-sweat mechanisms this metabolic heat needs to be lost via the sweating response and the subsequent evaporation of that sweat.

Two main factors contribute to the decrease in performance in stressful environmental conditions: heat production and heat loss (for more on heat loss, check out this blog on Why do humans sweat so much?).

But in hot conditions, the amount of sweat you need to produce increases, as you receive less cooling via non-sweat mechanisms. Similarly, as the amount of water vapour in the atmosphere increases (absolute humidity) the ease at which your sweat evaporates reduces. This means that your primary heat-loss mechanism during exercise (the evaporation of your sweat) doesn’t work as well, which increases your core temperature. As your body temperature increases, your relative VO2 max. reduces, meaning that your relative exercise intensity becomes higher as you get hotter and this results in your performance dropping both because of physiological factors (i.e. increased thermoregulatory demands (i.e, skin blood flow, sweat rate and reduced blood volume if dehydration occurs), inflammation in the gut, less neuromuscular activation) and psychological mechanisms (i.e. less willingness to exercise).

A severe increase in internal body temperature (40ºC [104ºF]) can cause serious issues, including heatstroke and death. So, what can you do to ensure you adequately train in the heat, reach your goals, and avoid potentially fatal consequences?

Analyse your circumstances

It's all about your individual needs. You need to understand where you are physically, what your history is, and what you can tolerate.

Firstly, identify in which conditions and context you will exercise. Is it a three-day vacation in a hot climate, or is it a race that you want to win?

If you will only be out in the heat for a couple of days and the aim is to do a few workouts so you don't lose fitness, you probably won't need to do anything specific besides riding early in the morning in order to avoid high temperatures.

If you want to perform in the heat, you need to work on it.

Assuming you want to avoid a huge drop-off in your performance while riding in the heat, you'll need to be able to deal well with conditions.

If you consistently train and expose yourself to hot or warm/humid conditions, you might not need further adaptations to the heat, and may even benefit from some cool weather training to increase mechanical workloads

In contrast, if you live in the north of Canada, where temperatures reach 30ºC (86ºF) a couple of times a year, your approach should be completely different because you'll need an 'adaptation protocol' to perform in the heat.

The adaptation protocol

A factor to consider when planning an adaptation protocol is your actual fitness and your recent training history. With good aerobic fitness, core temperatures are lower in normal conditions and heat can be dissipated more efficiently.

On the other hand, if you're new to the sport, coming out of the off-season, or a long winter, or maybe you’re a sprinter who doesn't have very good aerobic fitness, to get the most out of any heat training you’ll need to focus on a 3-4 week aerobic training block.

A plethora of adaptions occur when adapting to heat, some primary adaptions are: your core temperature decreases, blood plasma volume increases, you start sweating sooner and at a faster rate after starting exercise and your maximum sweat output increases, which leads to greater cooling capacity.

In order to choose your protocol, consider two factors: what kind of protocol do you follow and how long do you follow it?

The main stimuli to drive the adaptations are increasing core temperature and forcing a high amount of sweat. Here you may consider what facilities you have. Do you live in a hot environment? Do you own an indoor trainer? Do you have access to a stationary bike?

If you live in a hot environment, go out in the middle hours of the day and try to find climbs so you go slow and get hotter. Keep the sessions at 60 minutes at first and progress to a maximum of 2 hours in the heat. Getting your body temperature hotter (39ºC / 102ºF) or going for longer (>2 hours) won’t lead to more adaptation and will only lead to more stress, which may impact your recovery and ability to recover from the rest of your training.

If you don't have the luxury of warm and sunny conditions, you can do heat training in your basement or another (preferably small) room. Hop on the trainer, turn the fan off for the first 15 minutes (to allow body temperature to increase)and turn a heater or two on (or put on some additional clothes (bib tights, winter jersey etc). At this point, it would be advisable to use a device that can give you an idea of your body temperature so that you get hot enough, but not too hot, such as the CORE Body Temperature sensor.

And, if you don't own a trainer, try borrowing one from a friend or exercise in a gym with a stationary bike.

The duration of the workouts should be around 60-90 minutes, without the need to go too hard, but with enough intensity to sweat heavily. The goal of the session is to bring your body temperature up quickly - to around 38.5ºC (101.3ºF) and then reduce your effort to maintain your body temperature between 38.5 and 39ºC (102.2ºF)for the remainder of the session.

Regarding the duration of the protocol, about two weeks is the sweet spot, but if you’re really fit you could adapt in just one week. As more well-trained individuals tend to already have partial adaptations to the heat.

So, four workouts per week in the heat for one week if you’re recently well-trained, or two weeks if you’re not so recently well-trained, will put you in a good place to tolerate the heat.

Remember to build it up: start with shorter and easier sessions, and finish it with longer and harder ones.

Cooling in the heat

Even though you may have prepared as well as you can, come race day you'll still want to keep yourself as cool as possible to perform at your potential.

If you're not looking for maximum performance, follow these general guidelines:

  • Follow a strong preloading strategy to start well-hydrated
  • Measure your sweat rate in prior session so you can know roughly how much fluid you need to replace with. You can calculate your sweat loss and sodium loss, and tailor your drink to suit your specific needs
  • If you're trying to maximise performance, you should consider dedicated cooling methods during your race. You could try to stay cool with an ice vest during your warm-up if resources allow, or combine the ice vest with a fan if you are on a static trainer. But don't cool the legs, as this would impair the benefits from the warm up, and don't cool yourself if your event is a short race where sprinting is key (e.g. track racing) because this might affect your sprinting performance.

A useful cooling technique during a race is to put an ice sock underneath your jersey or in the neck area.

If it's a multi-day event, try cooling yourself as early as possible after each stage to improve recovery (an ice bath might be the perfect example here), and consider avoiding a warm down, as this will delay the cooling and add more heat.

How you should train in the heat

How you train in heat is dependent on your goals, history and circumstances.

If you're likely to experience heat for a only few days and just want to do a couple of workouts, adjusting the time of the ride according to the temperature will help you deal with it.

On the other hand, if you want to perform on a given day in the heat, a proactive heat adaptation protocol and cooling strategy are needed to get the most out of yourself.

But, if you just want to keep training during the summer months, try building things slowly. Consider what your history is, and how you deal with heat, and plan accordingly.

If you don't deal well with heat, but you need to keep training, apply an adaptation protocol, lower your targets for the workouts, build gradually (i.e. start with easy rides in the heat and carry out harder workouts early in the morning), but importantly stay consistent.

The best adaptations to the heat come with heat exposures that are close together (i.e. every 1-2 days). Heat is an additional stress, and, if you're not adapted, you'll run into problems if you keep training in the same way as if you were in cooler conditions.

So, look at your situation, adapt the training to your needs and abilities, and don't forget the basics: listen to your body and hydrate.