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Racing & planning
Heat & altitude preparation
The heat-acclimation protocol (sessions, sauna alternative, safety) and how to handle racing at altitude.
Heat: why it decides races
Unacclimated athletes lose 5-15% of their performance in the heat — and
hot races are decided by who prepared for the heat, not who ignored it
(Frankfurt 2026 made this brutally clear). The good news: heat adaptation
is fast, reliable, and trainable in the last two weeks before a race.
The Grepiac heat protocol
Timing: 8-12 heat sessions across the final 2-3 weeks before a
hot-forecast race. Adaptations begin around day 4-5, are largely complete
by day 10-14, and fade after about a week — so finish the block close to
race day and top up with 1-2 sessions if there's a gap.
Active sessions (preferred): the library has two ready-made sessions —
Heat Acclimation Ride — 60min and Heat Acclimation Run — 40min. The
rules that matter:
- Cap effort by heart rate (Zone 1-2), not power or pace. The
adaptation driver is core temperature and sweating, not watts. Power
WILL be lower. That is the protocol working, not fitness disappearing.
- Indoors: no fan, warm room, overdress. Outdoors: the warm part of the day.
- You should be sweating freely by ~20 minutes.
- Weigh yourself before and after, log the loss in the sweat-rate
calculator, and rehydrate ~150% of it over the following hours.
Passive alternative (for hard-training days): 20-30 minutes of sauna
or a hot bath immediately after a normal session gives a similar signal
with no extra training stress. Useful when the taper still contains
quality work you don't want compromised.
What to expect: within 10 days — more (and earlier) sweating, lower
heart rate at the same effort, better mood in the heat, and a real pacing
edge on race day. Plasma volume expands too, which is why the first
adapted sessions can feel oddly strong.
Heat safety — read this part twice
- Stop immediately on dizziness, nausea, headache, chills or
goosebumps in the heat — those are heat-exhaustion warning signs, not
toughness tests. Cool down, drink, done for the day.
- Skip heat sessions when ill or feverish, after alcohol, or on very poor
sleep.
- Cardiovascular conditions or pregnancy: medical clearance first, no
exceptions.
- Never bolt heat onto key intensity sessions — heat work is easy work.
- Kids in the car, pets on the run, locked bathrooms for hot baths — think
through the ordinary-life safety around deliberately overheating yourself.
Altitude: what actually changes
Above ~1,500m the air holds less oxygen: threshold power/pace drops
roughly 5-8% per 1,000m of elevation, heart rate and breathing run
higher at any effort, and fluids disappear faster through breathing.
Unlike heat, meaningful altitude adaptation takes 2-3 weeks of living
there — which most age-groupers don't have. So the game is management,
not adaptation:
- Arrival timing — pick one: arrive 2+ weeks early (real
acclimatisation) or as late as possible (<24-48h before racing) —
you race before the worst of the acute response sets in. The worst
window is days 2-5 at altitude.
- Adjust pacing, not goals: take your race targets down ~5-8% per
1,000m and cap by heart rate and feel in the first half. The field slows
too — percentile matters, not watts.
- Hydrate more than feels necessary and expect worse sleep the first
nights (higher altitude = lighter sleep; sleep low if you can choose).
- Iron status matters if you attempt a real altitude block — check
ferritin with your doctor before a camp, not after it fails.
- Training camps at altitude are a separate project (live high / train
low, reduced intensity the first week) — talk to your coach before
booking one; they cost recovery as well as money.
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