SYNTH-06 · Guide
Altitude, heat and iron
Measure iron before any altitude block, choose ONE environmental block and dose it properly, expect a few per cent at best with a large individual spread, and when the race itself is high or hot prepare for that environment and never drink more than you lose
The question it answers
"Is an altitude camp worth it, how high and how long?", "do I need iron first?", "heat or altitude?", "my race is at 2000 m (or in the heat, or both) — what do I do?" The heat protocol itself is SYNTH-04; drinking is SYNTH-68; this entry decides which block, in what order, and what has to be in place before it.
Default (what to prescribe first)
1
Measure iron before planning altitude. Iron deficiency is found in ~15-35% of female and ~5-11% of male athlete cohorts, exercise-induced hepcidin is a contributing factor, and hypoxia from altitude training is among the things that shape iron status (REF-340, B+, narrative review; it gives no ferritin thresholds, doses or timing windows).
In 178 athletes (98 males, 80 females) who spent 2-4 weeks at 1,350-3,000 m, haemoglobin mass rose 1.1% with no iron supplement, 3.3% with 105 mg and 4.0% with 210 mg of oral iron a day, and serum ferritin changed by -33.2% in those who took none (REF-969, B, retrospective and observational: the dose was not randomised, no ferritin cut-off, no performance outcome) — iron status is part of a camp's result; it is not a case for every athlete to take iron.
Not from a study; the base's own practice: a blood panel (ferritin, haemoglobin, transferrin saturation) 8-12 weeks before a camp, read with a physician.
2
Pick one environmental block, not two. Combining heat and altitude training does not appear to improve temperate, sea-level performance more than either alone (REF-199, B+, narrative review; hot or high target events are outside its question).
3
If the block is altitude: live at 2200-2500 m for about 4 weeks, at least 12 h a day (20-22 h/day at 2500 m is sufficient; more than 16 h/day adds benefit) for a haematological effect (REF-209, B+, narrative review — the authors' synthesis, not one trial).
In 48 collegiate distance runners randomised to live at 1,780, 2,085, 2,454 or 2,800 m for a 4-wk live high-train low camp, the sea-level 3,000-m time trial improved only in the 2,085 and 2,454 m groups, although erythrocyte volume rose in all four (REF-971, B+; no sea-level control, within-group changes, no effect sizes) — the authors' target is between 2,000 and 2,500 m, and higher was not better.
4
If the block is heat: the protocol is [SYNTH-04]. After 3-5 weeks of heat training a robust rise in haemoglobin mass has been reported repeatedly, the performance gain is small, and the authors conclude heat might substitute for altitude training (REF-736, B+, narrative review).
5
Promise little. Natural live-high-train-low gave a likely +4.2% (90% CL ±2.9%) in maximal endurance power in subelite athletes and a possible +4.0% (±3.7%) in elite ones, with part of the effect attributed to placebo, nocebo and training-camp effects (REF-210, A, 51 studies, 2009). For a given hypoxic dose the individual response ranges from almost nothing to very large, and whether one athlete's response repeats at the next camp is unknown (REF-736).
Decision (who → what)
| Situation | What to do | Source and how sure |
|---|---|---|
| Sea-level, temperate target; one block possible | Heat or altitude — either is defensible; heat is the cheaper experiment (no travel — the entry's reading, not a finding of the review). Not both | REF-736 B+ (no winner declared); REF-199 B+ |
| Altitude residence possible for ~4 weeks | Default 3. Inference, not tested: keep the hardest sessions as low as the location allows | Dose REF-209; classic live-high-train-high was unclear (+0.9 ± 3.4%) in subelite athletes and the low-training inference is REF-210's own |
| Only 2-3 weeks at altitude | Go, but do not promise more haemoglobin: non-haematological gains (economy, buffering, ventilatory response) need under 3 weeks (~18 days) and can be reached up to 3100 m | REF-209 B+ |
| No altitude residence | Not passive hypoxia at rest: the review finds hypoxic training more beneficial than passive hypoxic exposure. Use heat for the blood adaptation | REF-209. In 47 elite cyclists, 5 weeks of 5 × 50-min heat sessions a week raised haemoglobin mass 4.0% (women) and 3.5% (men) and improved lactate threshold, VO2max and 15-min power in cool conditions (REF-469, A-). In 10 well-trained runners, 5 weeks of 5 × 45-min hot-water immersion at ≥40 °C: +33 g haemoglobin mass, VO2max +2.7 mL/kg/min (REF-135, B) |
| Target race in the heat | Heat acclimation by SYNTH-04, not altitude. On the day: plan drinking from a weighed sweat rate, never more than the measured loss, and let thirst override the plan downward (SYNTH-68); cool before and during a long effort | Five exposures did not raise the heat-tolerance limit and nine did, and the lower rate of core-temperature rise appeared 4-8 days after the block (REF-3489, B+, non-athletes — so do not butt the block against the start: that entry's inference). Precooling helped prolonged exercise (d = 1.91) and impaired sprints (d = −0.26) (REF-111, A-). Menthol changes thermal sensation, not core temperature (SYNTH-25, B-) — it is not permission to pace harder |
| Target race at altitude, athlete not acclimatised | Set expectations before the trip; pace by effort and heart rate, not sea-level power (the base's own practice). Not from a study; the base's own practice: arrive as early as life allows | On acute exposure VO2max fell 6.3% per 1000 m (individual range 4.6-7.5%), linearly from 300 to 2800 m and already at 800 m (REF-706, B, n=8 runners). At a simulated 3000 m the fittest lost most and lactate-threshold VO2 fell too (43.5 → 36.5 mL/kg/min) (REF-708, B, n=12) — zones shift, not only the ceiling |
| Race both high and hot | Not from a study; the base's own practice: prepare for the stressor that will be larger on the day; heat exposures by SYNTH-04 ending about a week out; altitude by early arrival. Inference: do not start two new stressors in the same week | No entry tests altitude and heat in sequence; REF-199 says sequential exposure needs further study |
| Low ferritin, heavy periods, or both | Physician first (REF-573); the base's own practice: the camp waits. Add a heavy-bleeding question to intake | Heavy menstrual bleeding was reported by 36% of London Marathon runners and 37% of elite athletes; only 22% had sought advice (REF-573, B, survey, n=1862). A combined pill cut menstrual blood loss ~44% and raised ferritin only in the two women with depleted stores (REF-577, B, n=20 non-athletes, 1992 — a physician's conversation, not a coaching prescription) |
| Signs of low energy availability | Not from a study; the base's own practice: no altitude block and no deficit during one; screen by SYNTH-54 | The IOC consensus lists a reduced response to altitude training, low iron status and reduced iron absorption among the consequences of low energy availability (REF-341, A; full-text table) |
How to progress / periodise
Iron, before and during. Not from a study; the base's own practice: aim for ferritin ≥ 40-50 ng/mL before an altitude block and re-test about 4 weeks later; REF-340 gives no threshold and says only that iron status should be measured, not assumed. If a physician prescribes oral iron, the schedule is the prescriber's.In 40 iron-depleted women (ferritin ≤25 μg/L; not athletes) 60 mg on alternate days was absorbed better than the same doses on consecutive days (21·8% versus 16·3% fractional absorption), and in 20 women splitting 120 mg into two daily doses did not improve absorption (REF-970, B+, two open-label randomised trials; absorption and hepcidin only — no ferritin, haemoglobin or performance outcome; transfer to athletes and to men is inference) — which favours a single morning dose on alternate days.The altitude figures in REF-969 are for daily doses; no entry compares the two schedules at altitude. Not from a study; the base's own practice: with vitamin C, away from tea, coffee and calcium. Inference from the hepcidin mechanism REF-340 names (no window is given there): not in the hours after a hard session. The base holds no stop threshold; the prescriber sets it.
First days high. Sea-level power targets do not apply: the −6.3% per 1000 m slope gives about −13% of VO2max for 2000 m gained and −16% for 2500 m (the linear arithmetic carried in REF-706, valid only inside its 300-2800 m range and for the unacclimatised).Not from a study; the base's own practice: easy by heart rate and RPE for the first 3-5 days, intensity rebuilt over the second week, and no power-based fitness judgement or threshold re-test from a session ridden high.
Monitoring. Subjective self-report measures tracked training load with better sensitivity and consistency than resting heart rate or blood markers (REF-368, A, systematic review of 56 studies; not studied at altitude — transfer; the short daily format is the base's own practice); HRV is read as a per-athlete rolling trend, not a daily verdict (REF-361, B+).Not from a study; the base's own practice: morning resting heart rate and wearable SpO2 are trend signals only — the base holds no validated cut-off for either at altitude.
After the camp. No entry gives a post-camp performance window or the rate at which haemoglobin mass returns after descent, so any "race N weeks after coming down" rule is practice, not a finding of this base. The taper is unchanged: SYNTH-34.
Heat last when both are used. Not from a study; the base's own practice: because no entry measures how fast heat adaptations fade (SYNTH-04), the heat block sits nearer the event than the altitude block.
When NOT to use it / red flags
No iron without a blood test. Not from a study; the base's own practice: supplementing blind can miss a real deficiency or load an athlete who does not need it; anaemia, very low ferritin or heavy bleeding go to a physician (REF-573).
Not before the basics. The authors of REF-736 say heat training should probably wait until the rest of an athlete's preparation is in place; inference: the same holds for a camp when sleep, fuelling or consistency is the real limiter.
No energy deficit at altitude (REF-341; the rule against pairing restriction with hard training is the base's practice in that entry, not the consensus's).
Do not "hydrate aggressively" before or during a hot race. Drinking beyond losses is the cause of exercise-associated hyponatraemia; thirst is the default and any plan is capped by measured sweat loss (SYNTH-68, B).
Do not repeat a camp because the last one "worked" — individual repeatability is unknown (REF-736).
Not from an entry in this base; standard safety practice: at altitude a persistent headache with nausea, dizziness, unusual breathlessness at rest or a cough that worsens means stop training and seek medical advice — not a lighter session.
What the evidence does and does not show
Shows: an altitude dose that authors of a narrative review consider sufficient (REF-209); a few per cent of sea-level endurance power from natural live-high-train-low, with wide limits and placebo effects (REF-210); haemoglobin mass rising after 5 weeks of heat in elite cyclists and well-trained runners (REF-469, REF-135); no added benefit from stacking heat and altitude for a temperate sea-level race (REF-199); a linear loss of VO2max on arrival at altitude, larger in the fittest (REF-706, REF-708); iron deficiency is common (REF-340); haemoglobin mass rose more at altitude in athletes taking daily oral iron (observational, REF-969); a 4-wk camp improved a sea-level time trial only in the groups living at 2,085 and 2,454 m (REF-971); and heavy menstrual bleeding is common and mostly unmanaged (REF-573).
Does not show: any ferritin threshold, or a randomised iron dose that improves the altitude response or performance; how many days of acclimatisation restore performance at a given height; when to race after a camp; whether heat before altitude protects against anything; a head-to-head of heat versus altitude in amateurs; altitude outcomes in Tier 1-2 athletes or in women specifically (REF-469 is the one entry that reports women and men separately, for heat).
Evidence gaps
Timing of the return to sea level and decay of haemoglobin mass after a camp. No entry (REF-971 tests living altitude, not timing).
Time course of acclimatisation for competing AT altitude; altitude illness screening. No entry.
Altitude and heat in sequence, and heat acclimation's effect on performance in hypoxia. No entry.
Decay of heat adaptations (also a gap in SYNTH-04).
How this entry was checked and changed
Why this level
(altitude dose on a B+ narrative review; the sea-level gain on an A meta-analysis from 2009 with wide confidence limits; heat as a substitute on a B+ narrative review, one A- RCT in elite cyclists and one B crossover in runners; arrival losses on two small B laboratory studies; iron on a B+ narrative review that gives no thresholds, a B observational dose analysis and a B+ absorption trial in non-athlete women; living altitude also on one B+ randomised trial without a sea-level control; ferritin targets, the other iron habits, block order and camp management are house practice)
Content correction 2026-09-27
Heat gains "7-14 days of 60-90 min/day", "plasma volume +5-12%", "HR lower by 5-10 bpm" (unsourced) -> traced to REF-3491 (8 ± 4 exposures of 90 ± 36 min; plasma volume +5.6%; end-exercise HR −17 bpm) and REF-001 (+6.5%); aldosterone mechanism and sweat onset/sodium labelled inference/practice.
"Effects decay within 2-4 weeks" -> no entry measures decay (REF-002 no longer carries a decay rule); labelled practice.
Altitude "Hb mass ~3-6%", "20-30% non-responders", "2200-2800 m" -> +3-5% at 2000-2500 m over 3-4 weeks (REF-209, REF-210); non-responder share labelled practice; day-by-day timeline labelled inference.
"Cross-protection (REF Chapman 2014; Lorenzo 2010)" -> Chapman is not in the base and REF-001 measures no altitude outcome; rewritten as inference via plasma volume, with REF-210's unquantified cross-tolerance note.
Scenario A "adaptations peak ~2 weeks post-altitude" -> REF-210 puts the window 1-3 weeks post-camp and Hb mass back to baseline 2-3 weeks after descent; the tension with a camp ending 5 weeks out is now stated.
"see REF-176 if in base" for cooling -> REF-176 is a METs-classification paper; replaced with REF-111 / REF-113 (pre-cooling).
Iron "40-80 mg elemental Fe", "≥ 40-50 ng/mL", "re-test at 4 weeks", "discontinue ≥ 70-80" -> REF-340 carries 65-200 mg alternate-day, ≥ 35-50 adequate (some advocate ≥ 50), re-test q3 months; house targets labelled practice.
HRV "(REF-361) expect 5-15% decline in first week, recover by week 2" -> REF-361 now says HRV is a per-athlete rolling trend with equivocal direction in elites; the numbers are labelled practice.
Wellness "(REF-368) flag if any item drops > 1 point for 3+ days" -> REF-368's rule (2+ points on one item or 1+ on the 3-day mean) is the base's practice, labelled so.
Taurine: sweat "+12-15%" -> +12.7% acute and +8-15% local sweat with multi-day loading (REF-497); "≤ 3 mg/kg caffeine compatible" labelled inference (untested).
Scope "Section 8 (heat), Section 13 (altitude)" -> Section 1 and Section 14, where those entries live.
(sync 2026-09-27, after the full-base pass) REF-209 "Hb mass +3-5% over 3-4 weeks, +1-3% VO2max, >12 h/day at ≥2100 m for ≥3 weeks", "block 4-6 weeks before a mountain race", "lists heat as a partial substitute" -> corrected entry (now B+): 2200-2500 m, ~4 weeks, ≥12 h/day (20-22 h/day sufficient, >16 h/day adds), non-haematological gains in <3 weeks; no percentages; no race-timing rule; heat alternative is a base-practice line. Restated in the timeline, Scenario A and C.
REF-210 "performance window 1-3 weeks post-camp, Hb mass back to baseline 2-3 weeks after descent", "notes cross-tolerance" -> not in the current entry (a 2009 meta-analysis: natural LHTL +4.2% subelite, possible +4.0% elite, placebo/camp effects); claims removed, its actual estimates added. (REF-210 was not in this sync's change list; fixed because the SYNTH contradicted the current entry.)
REF-337 "sets ferritin ≥ 35 ng/mL" -> REF-337 is now a C+ methodology review with no ferritin target; citation removed.
REF-3491 "8-10 exposures of 60-90 min" -> that is the base's working prescription; the pooled mean is 8 ± 4 exposures of 90 ± 36 min; the 10-14-day kinetics labelled full text. REF-334b "passive heat alone is trivial" -> restated as post-exercise heat added to training (ratio 1.04, CI 0.94-1.15, low certainty). REF-3489 population (non-athletes) and the inference label added.
REF-497 multi-day ~3 g/day loading, +8-15% local sweat and the caffeine + taurine null -> from cited studies not checked against their abstracts; labelled. Level parenthetical "A-level primaries" -> REF-001, REF-209, REF-340 are B+; REF-3491 A-.
Resync 2026-09-28: REF-340 numbers no longer in the corrected entry -> "hepcidin spike 3-6 h", "menstrual losses 5-15 mg/cycle", "iron demand ↑ 2-3× at altitude", "≥ 35-50 ng/mL adequate", "65-200 mg elemental Fe, alternate-day superior" and "re-test every 3 months" removed or relabelled base practice/inference; REF-340 now carries only prevalence (~15-35% female, ~5-11% male cohorts), the hepcidin mechanism without a window, and altitude as a named factor.The earlier note in this section that REF-340 carries 65-200 mg, ≥ 35-50 and q3-month re-tests is superseded.
Resync 2026-09-28: "3-11% of males" -> 5-11% of male athlete cohorts (REF-340).
2026-09-28: the 10-14-day kinetics line re-read against the open-access full text of McDonald 2025 (REF-3491, PMC12122934): confirmed, location added.
Resync 2026-09-29: REF-341's caloric-restriction line is now labelled the base's practice, not a consensus finding; the 'What NOT to do' bullet attributed that rule to REF-341, so it is relabelled as practice, and the unsourced 'LEA risk amplified' is replaced by what REF-341 does carry (full-text Table 2: reduced response to altitude training, low iron status, reduced iron absorption); cross-reference gloss reworded to match.
2026-10-01: rewritten in the decision-framework format; the default changed from a 12-week iron → altitude → heat sequence to "measure iron first, pick ONE environmental block (altitude 2200-2500 m, ≥12 h/day, ~4 weeks per REF-209, or heat per SYNTH-04), expect a few per cent with a large individual spread".Contradictions resolved: "hydrate aggressively day-of-race" removed and replaced by SYNTH-68 (thirst, never more than losses); the heat mechanism, dose and maintenance numbers replaced by a pointer to SYNTH-04, and the "gains fade within 2-4 weeks" assumption dropped (SYNTH-04: no entry measures decay); the taurine section reduced to a pointer to SYNTH-67; taper pointer SYNTH-05 -> SYNTH-34.Folded in: REF-736, REF-199, REF-469, REF-135, REF-464, REF-706, REF-708, REF-573, REF-577.Unsourced camp numbers removed (intensity −20% for 3-5 days, SpO2 88-90%, resting HR +3-5 / +10 bpm, HRV dip, non-responder share, wellness-item thresholds, iron stop at 70-80 ng/mL); the house ferritin target ≥ 40-50 ng/mL is kept and labelled in its own sentence (REF-340 points here for it). Level B+ -> B; Type -> Decision framework.
Verification 2026-10-01: all 19 cited REF entries opened in KB.md; every number in the Default and Decision table (2200-2500 m, 4 wk, 12/16/20-22 h, +4.2±2.9 / +4.0±3.7 / +0.9±3.4, Hbmass 4.0/3.5 %, +33 g, +2.7 mL/kg/min, d 1.91/−0.26, 6.3 %/1000 m, 4.6-7.5 %, 43.5→36.5, 36/37/22 %, ~44 %, 1 g≈4 mL/min, +1.9 g [0.6,3.2], taurine 50 mg/kg/10 %/35 °C/n=11) matches the entry. Levels and designs next to refIds match the head blocks. No NUMBER, LEVEL or SOURCE findings.
Verification 2026-10-01: Level B is honest (narrative reviews B+, one 2009 A meta with wide limits, small B lab studies; practice lines are labelled). No LEVEL-OVERALL.
Verification 2026-10-01: outside this SYNTH but pointing at it — REF-210 Practical Application says 'the race-timing window after descent [is] set out in SYNTH-06', while SYNTH-06 states 'No entry gives a post-camp performance window'. The dangling pointer is in REF-210, not here. REF-736 Limitations calls REF-199 'the systematic review with meta-analysis'; REF-199's own head block says narrative review, B+ (SYNTH-06 cites it correctly).
Verification 2026-10-01: REF-340's second source (Pedlar 2018 DOI) did not resolve per the entry's own Limitations; nothing in SYNTH-06 rests on it.
Verification 2026-10-01: the altitude-illness red flag and the Drake-style external lines are correctly labelled 'Not from an entry in this base'.
2026-10-01: hot-race row aligned with SYNTH-68: in heat a plan from a weighed sweat rate capped at the measured loss, not thirst alone.
2026-10-01: level tags next to cited frameworks updated to their current levels after the independent audit.
2026-10-01: title no longer says "drink to thirst" for a hot race — in heat the body text plans drinking from a weighed sweat rate, capped at measured loss (SYNTH-68).
Revision 2026-10-01: folded REF-969 (Govus 2015, B, observational, 178 athletes) into Default 1 and 'Shows'; REF-971 (Chapman 2014, B+) into Default 3 — it supports the existing 2200-2500 m default (improvement only at 2,085 and 2,454 m, not 1,780 or 2,800 m); default unchanged.
Revision 2026-10-01: the oral-iron schedule line lost its practice label only for 'one morning dose on alternate days', which REF-970 (Stoffel 2017, B+) states — in iron-depleted non-athlete women, absorption outcome only, transfer labelled; vitamin C / tea / coffee / calcium stay practice.Tension stated in the text: REF-969's altitude figures are for DAILY doses (105/210 mg), REF-970 favours alternate days; no entry compares them at altitude; the schedule stays the prescriber's.
Revision 2026-10-01: Evidence gaps narrowed — the Govus/Stoffel candidate line replaced by what is still missing (randomised dose, ferritin cut-off, athletes); the 'Chapman 2014' timing line kept as a gap: REF-971 is the living-altitude paper, not a return-timing study. Level B unchanged; the Level parenthetical and lead now name the new sources.