Why train for the heat?
- To ↓ health risks such as heat exhaustion & heat stroke – a lesson I learned the hard way during my first attempt at the World 24-hour TT championships and countered with success the next year.
- To ↓ performance decrements in the heat – even the very best ultra athletes will experience a drop in performance during the hottest hours of the day.
- Muscles – which results in a ↓ in power and pace
- Brain – which results in ↓ in mental arousal
- Gut – which results in ↓ gastric emptying and ↑ inflammation & GI discomfort
- ↑ HR for the same power or ↓ in power
- ↑ Rate of Perceived Exertion (RPE)
- ↑ Thermal discomfort
And guess what further challenges your heat tolerance ? Sleep deprivation … so a double challenge for most ultra racers… Eventhough there is inconclusive evidence to claim that sleep deprivation impairs thermoregulation perse, psychological tolerance to the heat is diminished.
What adaptations can you achieve with heat training?
- ↓ risk of heat illness
- ↓ core & skin temperature during exercise
- ↓ HR at rest & during exercise
- ↑ sweat response: ↑ skin blood flow + ↑ sweat rate + earlier onset of sweating = better able to cool yourself
- ↑ fluid balance with ↑ thirst response + ↓ loss of sweat sodium
- ↑ blood plasma volume – also great for general endurance !
- ↑ thermal tolerance & comfort – feeling less hot
- ↓ RPE when exercising in the heat
In short, repeated exposure to heat stress, be that by exercising in natural heat or through articifical heat acclimation, enables you to better handle the heat, both physically and mentally.
Some of these adaptations happen fast, others take a little longer to optimise, but overall they do not only improve your heat tolerance and performance in the heat, your aerobic exercise capacity in milder temperatures may also get a boost !
How do you train for the heat?
Now let’s get into the exciting stuff. How can you actually ‘train’ for the heat ?
The main stimulus for heat adaptation is to get your body warmer than normal (a common practice is to aim for core temperature of ~38.5°C ) and to keep it this hot for 60-90 minutes per day. There are several strategies to induce heat adaptation in a safe and practicable manner. The decision to acclimatize by training in the natural heat or acclimate by using artificial heat remains a consideration based upon individual circumstance such as time, cost, logistics and training disruption.
Sure, a lovely scenario would be enjoying 2 or 3 weeks of cycling in the same hot environment as the upcoming race or event. But for most of us that is simply not possible … For the lucky few living in hotter climates, make the most of it ! But even that is easier said than done. For example, doing a block of heat training in the heat of the Australian summer when your key race is still 6 months away during European summer is of limited help and will still rely on a significant number of heat acclimation maintenance/top up sessions. Similarly, despite some transfer between environments, training or racing in dry heat is very different to humid heat !
However, this is where heat acclimation comes in: simulating hot ambient conditions by training in an environmental heat chamber (where the exact temperature and humidity can be simulated), or using passive heat acclimation techniques such as hot water immersion or jumping in the sauna immediately after your training session.
Let’s have a look at some of the methods, advantages and disadvantages in the overview below which was informed by Daanen et al (2018), supplemented with additional sources.
Note that in practice, riders and coaches often use a combination of methods based on time and resources available, training focus and travel opportunities.
My preference is for HWI immediately after exercise as this is the most time- and cost-efficient method for the majority of riders I coach. It also allows me to still schedule in some higher intensity sessions during the heat training block. Nonetheless, the added stress of the HWI sesssions on top of the training stress needs to be taken into consideration, which is where monitoring resting physiology data and subjective scores in my HRV4Training Coach dashboard comes in handy. In addition, I try to reduce/avoid heat stress during the final taper period, especially if the rider has the opportunity to still re-acclimate to the heat with some short rides in the hot sun prior to the race start.
Reading this blog about the benefits of heat training may have gotten you all worked up, but be warned that heat acclimation is hard work ! A hot bath after your bike session sounds great, but it is not as relaxing as you may hope … and (initially) you may certainly experience some discomfort both during these sessions (hot) and after these session, including potential for temporary ↓ performance, ↑ dehydration risk and most importantly an ↑ in strain.
That is why it is important to:
a) Only start heat acclimation sessions if you are 100% healthy – don’t even think about it if you are fighting off any illness or infection !
b) Keep exercise in the heat at low-intensity and/or apply the heat stress after the workout.
c) Consider working with an experienced coach who understands the physiology and can balance the additional heat stress on top of your training stress with the need for recovery and adaptation as well as the ideal timeframe and method(s) for your heat training block.
I had no idea that you could sweat so much and still exist in human form! Tbh, I really hated the hot baths, but I suspect that they made my body and mind better prepared for the heat that we encountered on day 3 and 4. I am, however, supremely grateful that we didn't have the 40°C+ of the previous weeks...
How long does it take?
Time course of heat acclimation adaptations with repeated training in the heat. Adapted with permission from Périard et al. (2015). Open access licensed under Creative Commons Attribution CC-BY 4.0
A short-term protocol (as little as 5 days) can already show some heat adaptation benefits, but longer protocols of 8-14 days will result in a more complete state of adaptation, especially for women. Even if for men 70-75% of the heat adaptation occurs within the first 7 days, full acclimatisation can take up to 2 weeks, so a longer protocol is still recommended.
Longer initial heat acclimation protocols can also result in slower decay rates. For example a short-term heat acclimmation protocol of just 5 days, saw retained adaptations for one, but not two weeks. Without further heat exposure, heat adaptations decline by ~2.5% per day, equivalent to ~35% after two weeks (Daanen et al. 2018). However, the good news is that, when undertaken within a month of the original acclimation period, heat adaptations are faster to regain !
Heat adaptations ↓ ~2.5% per day without heat exposure (Daanen et al. 2018). Acclimation periodization: acclimatize weeks in advance, maintain some adaptations with exercise & passive heat, re-acclimate with 2–3 sessions in Tokyo (Racinais & Périard 2020) #ESSTC20
— Inigo Mujika (En) (@inigomujika_en) November 16, 2020
7/10 pic.twitter.com/K8oWaVxnIE
Why does it take longer for women?
A review by Wickham et al (2021) proposes that the time differences may be a result of differing thermal load between the sexes.
That makes some sense, because if you get male and female participants to exercise at the same intensity (e.g. ~ 65% ̇VO2max ), females tend to perform significantly less total work (in kJ) per session than males (due to generally lower power output and lower body mass) and so there also is less metabolic heat production.
Adding to this, another study by Jessica Mee and colleagues at the University of Brighton (2018) found that women who received 20 minutes of sauna suit exposure immediately prior to short-term (5 days) heat acclimation saw accelerated adaptations compared to without the preload.
Another consideration for my female riders is where they are in their menstrual cycle and if they use the oral contraception pill. During the luteal phase of the menstrual cycle (after ovulation and before menstruation) there is a rise in progesterone which leads to an increase in core temperature by ~ 0.3 to 0.5 °C and a similar upward shift in the threshold for the onset of vasodilation and sweating. Note that the same applies to the active pill phase for oral contraceptive users.
This means that not only is it harder for female cyclists to handle the (humid) heat when they are in the luteal phase or on the pill, it also means that less metabolic heat production is required to achieve a core temperature of ~ 38.5 °C (often used as a target in heat acclimation protocols). In the aforementioned study the researchers speculate that this could thus limit the overall thermal load within heat acclimation sessions and reduce the magnitude of resulting adaptations.
Unfortunately there are not so many studies to draw on (yet). Female data remains sparse in exercise thermoregulation research, with the majority of studies not reporting on or not controlling for menstrual cycle phase. So, how to optimise heat acclimation for women in the meantime ? Here are a few ideas:
- Extend heat acclimation up to 8-14 days
- Or go for the shorter protocol, but include a short sauna primer or short sauna / hot bath booster after
- Start heat acclimation during the early follicular phase and complete in the late follicular phase before ovulation so the progesterone-driven increase in core temperature does not play a factor yet, plus the repeated heat stress is added at the time in the menstrual cycle when stress resilience is greatest.
What about peri & postmenopausal women?
When we think of menopause and the heat we often think of hot flashes (as the Americans say) or hot flushes (as the Brits prefer to avoid confusion with indecent exposure in public) as one of the most renowned symptoms of the menopause transition. Hot flushes are annoying at any time, but when they happen during exericse they can also limit power output…
Physiologically what is happening during a hot flush is best explained as your brain overreacting to temperature changes, sensing that you are too hot, when in fact you are not … As a result, heart rate increases anywhere from 5 to 25 beats/min, blood vessels widen and more blood is sent to the periphery (particularly blood vessels near the skin of head, neck, face, chest and upper arms) along with a sudden outbreak of sweat which then may leave you shivering the next moment… Hot flushes happen when there is an abrupt drop in sex steroid hormones. Although most common in peri- and post-menopausal women (estradiol decline along with reduced thermoneutral zone), they occasionally also happen in men such as when testosterone levels fall instantly and rapidly if treated medically or surgically for prostate cancer.
But in addition to hot flushes peri- and post-menopausal women also face the challenge of being less able to cool themselves down than younger women due to reduced thirst sensation, reduced vasodilation and reduced sweat response, whilst simultaneously enduring a higher core temperature during exercise (Amabebe et al, 2013).
All of the tips below on precooling and how to cool yourself down during exercising in the heat (ice socks, cold drinks, menthol, wetting your wicking sun sleeves, cap etc) work for all ages and also work for hot flushes.
In addition, as suggested by Stacy Sims in Next Level (p. 274), a pre-exercise dose of beta-alanine (a non-essential amino acid) can help with opening up the blood vessels and ward off the hot flushes, especially for women who can’t or don’t want to use HRT. What is more, if taken over a longer period, beta-alanine can elevate the carnosine content of skeletal muscle and increase the pH buffering capacity of the muscle. What does that mean ? Well, it may help delay the onset of both anaerobic and aerobic fatigue, allowing for longer and/or more intense training sessions, inducing potentially greater physiological adaptations and improved performance (Murphy et al, 2022).
To date there are no specific heat acclimation guidelines for peri- or postmenopausal women, or older athletes in general. In fact it has been suggested that VO2max rather than age is the differentiator factor. For example, a 2014 study investigating the effect of age on heat adaptations in younger (19-32) and older (50-63) highly trained male cyclists found that trained older adults can achieve similar relative reductions in core body temperature as younger adults, with only a small age effect for heart rate and skin blood flow adaptations in the older age group after six consecutive days of controlled intensity exercise-heat stress.
Nonetheless, preparation for competing in the heat is very important for older athletes as the risks of overheating and dehydration increase with age. For example, Stapleton et al (2015) compared 10 young (23±4 years, tested in the early to mid-follicular phase) and 10 older (58±5 years) post-menopausal females matched for body surface area and aerobic fitness. The women did three 30-min exercise bouts at incremental rates of metabolic heat production of 250W, 325W and 400W in 40°C heat with 15% relative humidity. They found that the older women stored more heat / had more difficulty getting rid of the heat than the younger women and this differential became more pronounced as the heat load increased. Core temperature also remained higher in the older females at the end of the final 15 minute recovery period.
How to manage the heat?
Start cool
There are various ‘pre-cooling’ techniques that can help to increase your capacity to store heat and increase heat transfer from the core to the periphery. These include wearing cooling vests or an iced towel around your neck, drinking slush puppies or cold water, mouth rinse with menthol, sitting near a cold air fan, immersing yourself wholly or partially in cool water and spraying yourself with cold water. As goes for most things related to racing, it is important to try these techniques out in training first if you are considering them for your race. Using a combination of these techniques usually has the greatest net effect, both physiologically and perceptually. A meta-analysis of 45 experimental pre-cooling trials (Bongers et al, 2020) found an average performance improvement enhancement of 4.7%, with cold water immersion being the most effective strategy. In practice, few ultra races (be they supported or unsupported) will start next to a cold river or dunking pool, but I have found the ‘ice sock‘ technique quite effective and practical, both before and during races. All it takes is bringing a pair of thin women’s tights you cut into pieces and fill up with some icecubes from a nearby hotel, petrol station or shop. Go easy on the slush puppies as too large a volume of iced drinks can cause some GI distress.
Keep cool
Depending on ride intensity, temperature and wind, the benefits of pre-cooling measures typically fade once you are ~30 minutes into your ride. So what you can do to stay cool or not overheat during your race?
As with pre-cooling, a cooling vest is the most effective strategy to stay cool and improve performance by up to 12% (Bongers et al, 2020). Unless you are racing with a support crew and follow car in the heat of Race Across America, you are unlikely to have this at your disposal during an unsupported ultra race (bar filling a hydration vest bladder with ice which then melts as drinking water …).
However, just cooling your hands can be pretty effective too with studies showing that 10 minutes of hand cooling in 15°C water can reduce core temperature by ~1°C and lower water temperature could potentially increase the rate of heat extraction. This is because your hands have high rates of heat exchange due to their large surface-to-mass ratio, low metabolic heat production, large blood supply and rapid cooling rates.
Another practical way to manage the heat is with cold drinks. This also makes you more likely to drink and drink more because cold fluids are more palatable. For even more impact, consider picking up the occassional slush puppy or pop a few ice lollies in your water bottle. Calippos are brilliant as you can easily use them the cool your skin too.
This may seem slightly counterintuitive but you can stay cooler for longer if you cover up with sun sleeves on your arms and legs. These coolers are made from a high-wicking material and protect your from the harmful UV rays, so reducing the need for suntan lotion. They work even better at keeping you cool if you wet them under a running tap or dunk them in a fountain at regular intervals. Various brands make these ‘coolers’, but you are most likely to find them if you check out shops oriented towards triathletes.
Let’s finish this long blog article with a fun question: “What is the most effective way to cool yourself: to drink the water or to pour it over yourself?” You often see the pro cyclists on TV pouring the content of their water bottles over their heads, but is this a smart move especially in case you may be down to your last water bottle in an unsupported ultra race ? Flip the image to find out.