September 22, 2026

The 5-Day Heat Blitz

Sometimes you don’t have weeks to get heat adapted – you have only days. While many people follow one of the 6- or 12-week schedules shown in our Boosting Your Heat Adaptation Score article, sometimes training doesn’t go as planned and you need immediate adaptation. And that’s when you can use the 5-day heat blitz. 

This protocol will raise your Heat Adaptation Score from zero to around 50%. This can let you manage a last-minute entry to a hot race, or even just deal with a forecasted heat wave. 

A few weeks ago, Metheven Bond used this protocol to prepare for ultra-cycling race Badlands and saw a +38W increase after 5 sessions.  

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The Blitz

The protocol is simple – one hour of cycling in the heat at a constant heart rate. Do this every day for 5 days. The details: 

1. Ride on the indoor trainer, either in a hot room (at least 35°C/95°F, >50% humidity), or while overdressed (details below). 

2. Start off at a mid-zone 2 power. It’s important to not overestimate this number. If possible, use the ERG mode to keep power constant. 

3. After 10 minutes, note your heart rate and keep it at this level for the rest of the session.  

4. As you heat up, you’ll need to adjust power downward. Try decreasing it in increments of 5–10 watts at a time as you notice heart rate creeping up. On Zwift, you can use the ‘decrease intensity’ buttons, maybe 2–4% at a time. 

5. Continue until you’ve ridden for a total of 60 minutes. Or, stop early and cool immediately if one of the below happens: 

  • Your core temperature reaches 40.0° 
  • Your Heat Strain Index reaches 7.0. 
  • You feel light-headed, dizzy, or nauseous, or experience cramps or a headache. 

6. Write down your ending power, core temp, Heat Strain Index, and heart rate. 

Tips for success

1. Be sure to hydrate and replace electrolytes before, during, and after the session. See this article for how to hyperhydrate. You may also want to measure how much sweat you lose during each session.  

2. If you’re overdressing, we suggest either a CORE heat training suit, or the following: 

  • Normal cycling kit as a base layer. 
  • A snug fitting rain jacket on top of the base layer. 
  • Possibly a thermal layer on top of the rain jacket (don’t wear it under the rain jacket…it will get sweat-soaked and cool you). 
  • Winter-weight leggings. 
  • Possibly a winter-weight hat. 

Understanding the data

1. A key metric is heart rate decoupling; at a given heart rate, how much did your power decrease from the beginning of the session to the end?  By the 5th session you should see substantially less decoupling when compared to the first. To calculate this: 

  • Subtract final watts from starting watts. 
  • Divide that sum by the starting watts to get a percentage. 
  • Example: If you started at 200w and ended at 170w: 
  • 200w – 170w = 30w. 
  • 30w / 200w = 0.15, or 15% decoupling. 

2. You can also calculate the average power to heart rate ratio. Simply divide your average power by your average heart rate. By session 5, this number should be higher than it was in session 1. 

  • For example, 200w divided by 145 bpm equals 1.38 w/bpm. 

3. Also track and compare your core temperature, Heat Strain Index, and Heat Training Load for each session. You may or may not see notable differences in these, because short-term adaptations may get blurred by the day-to-day variances in your physiology. 

4. Questions about your data? Please feel to contact us using the chat icon on homepage of corebodytemp.com.  

Train Hot, Race Cool

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