Prepare for Kona with CORE

Race your best by using CORE for heat adaption, identifying threshold core temps, honing a hydration plan, devising cooling strategies, and managing jet lag during travel.

The Hawaii Ironman World Championships is legendary for its heat and humidity. Each year at this iconic race, some of the world’s most well-trained triathletes experience epic meltdowns – and it’s generally from overheating. While the meltdown may be triggered by overly-aggressive pacing or hydration mistakes, the underlying cause is that the athlete’s core body temperature exceeded a sustainable threshold.

The most successful triathletes at Kona will have carefully prepared for the environmental conditions, with plenty of heat training and rehearsing of hydration and cooling strategies. A great resource is the Beat the Heat guide produced by the International Olympic Committee for the 2020 Tokyo Olympics. It gives an excellent overview of heat adaption and covers hydration and cooling strategies.

Here, we discuss how to use CORE in tandem with that guide to ensure your training and preparation is as precise, methodical and effective as possible. We cover heat adaption, threshold core temps, hydration, and cooling strategies. In addition, you can use your CORE to manage jet lag and ensure your circadian cycle is adjusted to local time by race day.

Heat adaption

The number of days required for heat adaption varies amongst individuals, but fourteen days works well for most athletes. Depending on travel plans and how heat training meshes with other workouts, you'll want to begin your heat training two to four weeks before your event. If you complete the heat training block more than a couple of days before competition, you'll want to do maintenance heat training until the start of the event. The IOC’s Beat the Heat guide provides good recommendations on this.

Here is a step-by-step summary of using CORE for heat adaption.

Step 1. Heat ramp test

Your first step is to complete a heat ramp test using your CORE sensor (instructions here). If your last heat ramp test was more than 8 weeks ago, or if you've made a significant change in the amount of heat training you’ve done since the test – you'll want to do another. Completing the heat ramp test will identify your heat training zone.

Step 2. Heat block training

The second step is to complete two weeks of heat block training. This involves training 45–90 minutes each day with your core body temperature within your heat training zone. For more details, see the CORE guide for heat training.

Warm climate or extra clothes

You can do heat training either by exercising in a warm climate, by wearing extra clothes, or some combination of both. Regardless of the method, your goal is to elevate your core body temperature into your heat training zone.

A few possible strategies:

  • Do your heat training at the event site for two weeks preceding the competition.
  • If you live in a warm climate but normally train during the cool of the morning/evening, do your heat training in the hotter part of the day.
  • Simulate a warm climate with indoor training in a heated room, using boiling water or humidifiers to increase the humidity.
  • During training, wear more clothes than normal. The right amount of clothes will depend on a mix of workout intensity, ambient air temperature, and humidity,

Passive heating

Passive heating can complement active heat training. It increases your heat training time with less fatigue and impact on normal training routines. A heat workout can be extended by using a hot bath (40 °C/104 °F) or sauna (70–90 °C/158–194 °F). Please note that the CORE device is not yet recommended for use in the sauna.

Core body temp is most relevant

The most important part of heat block training is raising your core body temperature into your personalised heat training zone for 45–90 minutes per day. This is true for whichever strategy is used for heat training, and regardless of the ambient air temperature.

Step 3. Heat training maintenance

If your two-week long heat block training ends more than a couple of days before your competition, you will need to maintain your heat training. This requires elevating your core body temperature into the heat training zone for 45–90 minutes per day, 2–4 days per week. This can be done with the strategies discussed in the heat block training section.

Threshold core temps

Over many weeks of training and some controlled testing, you can start to identify core body temperature thresholds. These are the core temps you can sustain for various durations. Just like cyclists know the watts they can sustain for 4 hours, for 1 hour, and for 20 minutes, triathletes can learn the core temperatures they can sustain for these times.

This knowledge can make for very strategic racing. For example, it could give the confidence needed to go hard for 10 minutes on the bike to bridge a gap without blowing up. Or it can help an athlete stay patient on the run and then really push the pace during the final 15k, confident of an ability to maintain an elevated core temp for an hour.

These threshold core temps can be a critical guide to race-day pacing – for some athletes, they are even more critical metrics than bike watts or run pacing. An athlete may choose to “race to temperature”, meaning that they keep their core temp below certain thresholds for each part of the race, regardless of what that means for the their watts or pacing.

Hydration strategies

Athletes cool themselves primarily through the evaporation of sweat from the skin. This evaporation cools blood that is flowing just-beneath the skin. Adequate hydration ensures that the heart can efficiently pump blood to both the muscles and the skin.

A typical way to calculate hydration needs is to determine sweat rates under race conditions (by simulating race pacing and ambient conditions). Training Peaks offers good instruction on how to complete a sweat rate test and Ironman describes a similar test using imperial measurement units. Athletes often try to replace fluids so that they lose no more than 2-3% of their body mass over the course of the competition, but this is a very individual decision, and some athletes will choose to lose more than that. There can be a limit to rehydration, as most find it difficult to digest more than 1 litre/hour of fluids. And athletes should never overhydrate, as that can result in the very dangerous hyponatremia.

After you’ve calculated your sweat rate and decided the range of dehydration you want to target, you can start training to those levels while wearing your CORE sensor. You can note how core temp varies at different levels of dehydration, and note how much power/pace declines at various core temps. This lets you hone your fluid intake volume and targeted dehydration level. You can strike the balance between dehydration and an acceptable level of core temp rise to what works best for you.

Cooling strategies

Cooling strategies can include much more than simply remaining hydrated. They also involve picking the appropriate clothing, and using techniques such as ice in the hat (while running) spraying the face with water, and the timing of water ingestion or dousing the body with water. All of these strategies can be tested in training while wearing your CORE sensor to see which are the most effective. The effectiveness of most of these is very individualised, and what works for one athlete (or in one set of conditions) may be less than optimal for another.

The most successful data-driven professional athletes are quite methodical about this testing. More information about cooling strategies can be found at this CORE article, and this one as well. A detailed review of scientific literature can be found at Cooling interventions for athletes: An overview of effectiveness, physiological mechanisms, and practical considerations.

Circadian cycle and jet lag

Hawaii time is 3–6 hours behind the continental US, 11–13 hours behind Europe, and 3–5 hours ahead of Australia. Athletes traveling to Kona can experience significant jetlag, which can have a major impact on the their race if not managed properly. CORE can help athletes overcome this jet lag by giving insights into their circadian cycle.

The circadian cycle is the body’s internal 24-hour clock. It regulates many of the body’s physical, mental and behavioural changes throughout the day and night. Most people know that circadian cycle is associated with sleep patterns. But the circadian cycle also influences muscle strength and flexibility, alertness, cognitive ability, appetite, and other hormonally influenced body processes.

The core body temperature is also closely linked to the circadian cycle. Core temp is at its lowest a couple of hours before waking up in the morning. It rises throughout the day, and for most people reaches an at-rest peak sometime between mid-day and early evening. This daily fluctuation spans approximately 0.5 °C/0.9 °F. By wearing your CORE 24/7 for a period of weeks before traveling, you should be able to readily identify these high and low points in your core temp.

You can then use this information to overcome jet lag. Adaption to the new time zone can be hastened by timing of bright light exposure, meals, exercise and perhaps melatonin. The strategies for overcoming jet lag are complex, and a number of techniques are detailed in a position statement from the European College of Sport Science called Coping with Jet Lag.

Whichever strategy is used, continued 24/7 monitoring of core temperature after arrival will let you know well you’re adjusting to local time, and if you need to take additional measures.

Race day stories

If you use your CORE for any or all of these preparation strategies we’d love to hear about it. What protocols did you follow in training? And how did it all work out on race day? Athletes and coaches using CORE are an innovative bunch and are advancing racing in state-of-the-art ways. Would you like to share your experiences with the CORE community? If so, please contact us – we’d enjoy featuring your story!