Athlete summary
If a race looks hot (start ≥ 28 °C, same band as the heat kit and fluid bump), Koyaro schedules a heat-acclimation block you can see on the race checklist and GET /races/{id}/heat-acclimation — dated exposures, a decay window, and a short re-induction if a recent camp has gone cold.
The default block is the McDonald 2025 mean protocol:
- 8 exposures (literature band 4–12)
- ~90 min each
- ~39 °C (chamber, hot outdoor, or equivalent heat stimulus)
- Timed to finish the day before the race so adaptations have not decayed
On those days the heat session replaces endurance volume. Do not stack a second long ride. Quality days stay. This is not a silent TSS rewrite.
What the engine locks
| Constraint | Engine behavior | Citation |
|---|---|---|
| Trigger | Outdoor hot / extreme (≥28 °C). expected_hot fills a missing forecast only | same bands as heat kit / fluid |
| Induction | 7–14 d; default 8 × 90 min @ ~39 °C | mcdonald-2025-ha-meta-regression, periard-2015-ha-adaptations |
| Abbreviated | 4–6 d still inside McDonald 4–12; under 4 d is too late | McDonald 8 ± 4 |
| Decay | Cubel full decay ~14 d; Périard window 14–28 d | cubel-2024-heat-hbmass-decay, Périard 2015 |
| Re-induction | 4–5 d after decay, not a second full camp | Périard “short re-induction” |
| Maintenance | 3×/wk while still inside the 14 d decay window | ronnestad-2022-ha-maintenance |
| Extended (opt-in) | Cubel 5 wk × 6×60 min when ≥35 d remain | Cubel 2024 |
| Volume | Replace endurance on HA days — no planner TSS mutation | |
| Scores | None — no HA % and no altitude-fitness number |
Cubel’s tHbmass +3% at 3 wk / +4% at 5 wk is literature on that protocol, not a number we invent for you.
What this is not
- Not a heat / altitude load multiplier. Fluid already scales in the heat; TSS does not change here.
- Not an altitude camp or Hbmass race-watt promise. Off-season heat can be a substitute stimulus for Hbmass; we do not score altitude fitness.
- Not a clinical heat-illness diagnosis.
- Not a reason to move HA sessions off a hot day — heat is the stimulus.
Literature
- McDonald, M. L., et al. (2025). Influence of exercise heat acclimation protocol characteristics on adaptation kinetics: a quantitative review with Bayesian meta-regressions. Comprehensive Physiology. doi 10.1002/cph4.70017
- Périard, J. D., Racinais, S., & Sawka, M. N. (2015). Adaptations and mechanisms of human heat acclimation. Scandinavian Journal of Medicine & Science in Sports, 25(S1), 20–38.
- Cubel, P., et al. (2024). Temperature. doi 10.1080/23328940.2024.2383505 — 5 wk × 6×1 h; tHbmass +3% / +4%; full decay ~2 wk.
- Rønnestad, B. R., et al. (2022). Heat training maintenance 3×/wk.