How to do a Heat Session
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During a heat training session, you perform exercise under heat stress. You will feel hot, you will sweat heavily, and your Heat Strain Index will be elevated. You can induce heat stress by exercising in warm and/or humid weather, wearing warm clothing, or some combination of both. When indoors, you’ll want to limit air flow – in other words, no fans!!
Heat Safety
Before doing a heat session, please read the article Heat Safety. Overexposure to high temperatures can be dangerous to your health and can lead to heat-related illnesses such as dehydration, heat exhaustion, and in extreme cases heat stroke with potentially fatal consequences. To reduce the risk of overheating and dehydration, drink plenty of water before, during and after heat training. If you experience heat-related symptoms such as dizziness, nausea, numbness, tingling, muscle cramps, headache, confusion, and/or fainting, stop exercising and consult a health care professional.
Pick a Warm Climate
Heat training without extra clothes is most effective at an air temperature of at least 30° C/86° F. High humidity may allow lower air temperatures to be effective without overdressing. In cooler environments, you can overdress. But if temperatures are below 15° C/ 59° F, you may struggle to create sufficient heat stress.
Or, Overdress
In cooler conditions, you’ll need to overdress. Think of this as creating a warm and humid microclimate around your body – your own personal heat chamber. The key to this is remembering that sweat-soaked clothes will cool you. Experiment with what works best for you, but the following is effective for most:
Torso:
- A long-sleeved nylon shirt against the skin
- Followed by a waterproof layer (ie. rain jacket) to prevent sweat evaporation
- Followed by a thick thermal layer on top of the rain jacket (the rain jacket prevents the thermal layer from getting sweat soaked)
Legs:
- Nylon/spandex tights
Accessories (possibly needed in cooler air temperatures):
- Warm hat
- Gloves
Alternatively – a paint suit (from a hardware store) can be very effective.
The Heat Session
Most people do heat sessions while cycling or running, although heat sessions using other forms of exercise are entirely feasible. Indoor training is extremely popular for heat sessions, as it is very easy to control the climate and intensity.
(Important: heat sessions should not be done while strength training, as overheating increases the risk of rhabdomyolysis.
Let’s get hot!
- Start the session with a short warmup.
- Then, increase your power/pace to a moderate zone 3 effort (75–90% of FTP for cyclists, half marathon pace for runners). This will quickly raise your core temperature and Heat Strain Index relatively quickly.
- Your goal is to reach of Heat Strain Index of 3.0–6.9. This may take 15–30 minutes.
Stay hot
- You’ll want to keep your Heat Strain Index between 3.0–6.9 for a continuous 30–80 minutes (45–60 minutes is most typical).
- To stay within this target range, you can adjust your intensity and/or clothing. Remember there is a lag between the time you make adjustments and when Heat Strain Index stops rising.
- Note that heart rate will rise even when power/pace stays constant. To avoid an excessively high heart rate, most people will keep heart rate constant and gradually lower power/pace. It’s not atypical to be in zone 1 power but zone 3 heart rate during a heat session. It’s also not atypical for runners to walk toward the end of a heat session.
- Thermoregulation is highly individual. For some athletes, a Heat Strain Index of 3.0 will feel very challenging. Others may need a value of 5.0 to get good adaptions. For more information, see the article Individuality of Heat Zones.
- If your first heat sessions seem too challenging, try spending only 20 minutes in the Heat Zone. Subsequent sessions will likely feel easier and you can gradually build up session durations.
- Don’t overdo it! Keep your core temperature below 39° C (102.2° F), Heat Strain Index below 7.0 (maximum…some individuals may have a much lower threshold), and limit the duration of the heat session to a maximum of 100 minutes.
- You’ll be sweating a lot, so remember to hydrate! Dehydration does not increase the quality of the heat session, and may even be dangerous. If you smell ammonia in your sweat, it is a sign that you are dehydrated.