Contrast

Heat adaptation

TheoreticalContrast’s own measure. It rests on known physiology but hasn’t been tested in a study, so read it as a personal trend.
How Heat adaptation is measured3 days off+¼ of what is left, per day of 30 min or more−2.3% a dayday 0day 24
Contrast's own model. The shape comes from heat-acclimation research; the estimate has not been tested.
What it is
An estimate of how adapted to heat you are, built from your recent days of sauna and hot bath, and checked against your heat strain.
How it is measured
A day with 30 minutes or more of sauna or hot bath counts in full; shorter days count in proportion, and days under 5 minutes don't count. Each day adds up to a quarter of what's left to gain, so most of it comes in the first four to six days. After three days without heat, it fades by 2.3% a day. The page also says whether your heart rate agrees: heat strain at the same heat should be falling too.
How to read it
Building, adapting and adapted describe the estimate, not a measurement. If it says adapted but your heat strain isn't easing, trust your heart rate.
What it cannot tell you
Contrast's own model, built from the timing seen in exercise heat-acclimation studies. Passive heat is a weaker stimulus than exercising in the heat, and people adapt at different rates.

Sources

Every one of these ships inside the app, with the finding written out so you do not have to open the paper to know why it is there.

  1. Pandolf KB. Time course of heat acclimation and its decay. International Journal of Sports Medicine, 1998.

    About three quarters of the heart-rate adaptation to heat arrives within four to six days of exposure.

    doi.org/10.1055/s-2007-971985

  2. Daanen HAM, Racinais S, Périard JD. Heat acclimation decay and re-induction: a systematic review and meta-analysis. Sports Medicine, 2018.

    Heart-rate adaptation to heat fades by about 2.3% a day without heat.

    doi.org/10.1007/s40279-017-0808-x

  3. Heathcote SL, Hassmén P, Zhou S, Stevens CJ. Passive heating: reviewing practical heat acclimation strategies for endurance athletes. Frontiers in Physiology, 2018.

    Passive heating used sessions of at least 30 minutes, with about six to seven sessions needed for adaptation.

    doi.org/10.3389/fphys.2018.01851