Science

The research the BLOCKS assistant answers from: 1,545 studies and 96 guides, each graded for how strong the evidence is and who it was measured on, with a link to the original paper.

Three kinds of entry: a principle is how the body works, agreed across reviews; a study is what one experiment measured; a guide is what to do.

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Heat, altitude & travel ✕

47 entries in Heat, altitude & travel

Sitting 30 min in 42 °C water after each of 9 HIIT sessions over 3 weeks gave 14 male cyclists no added gain over 34 °C water: the 20-km time trial improved 1.5% vs 1.7% (between-group p = 0.99, effect size 0.0), and lactate threshold, peak power, VO2max and muscle mitochondrial markers did not change significantly in either group; from the abstractMain caveat: 7 per group; allocation method not stated; men only; training status not given.Kjertakov 2025

In trained middle-distance runners who chose their own group (12 sauna, 8 control places), about 28 min in a 101-108 °C dry sauna after mostly easy runs, three times a week for 3 weeks, lowered heart rate (11 bpm more than control), rectal and skin temperature in a fixed-pace heat run and raised VO2max (+0.27 L/min) and speed at 4 mmol/L lactate (+0.6 km/h) more than training alone; 7 weeks added only 0.1 °C, and 19 of 37 starters dropped out injuredMain caveat: Self-allocation: runners chose their group, so motivation or other differences cannot be excluded; the authors argue both groups were equally invested.Kirby 2021

Does vaping tighten the airways?In 30 smokers, 5 min of use raised airway resistance by about 0.04 kPa/(L/s), meaning for exercise unknown, and lowered exhaled NO, measured at rest straight after. No exercise tested. From the…Main caveat: Abstract only; publisher page could not be opened.Vardavas 2012

What does a nicotine vape do right away?Across 27 articles (919 people), heart rate and blood pressure rose and exhaled NO fell; no significant spirometry change. Pooled before-after data, no exercise outcome; abstract.Main caveat: Abstract only: publisher page could not be opened; no heterogeneity, risk-of-bias or subgroup data seen.Larue 2021

What does a hookah do to exercise half an hour later?In 24 young male users, VO2 fell 1.86 to 1.7 L/min and oxygen pulse dropped in a fixed test; effort felt harder. Pilot, no control group. From the abstract.Main caveat: Abstract only; no SDs or P values for individual results.Hawari 2013

Does IQOS or a vape add CO like a cigarette?In 18 smokers new to both, 10 puffs raised exhaled CO only with the cigarette; nicotine rose with all (IQOS 12.7, JUUL 9.8, cigarette 20.4 ng/mL). No exercise; heart rate unreported.Main caveat: No exercise; markers and ratings only.Maloney 2020

Does heated tobacco spare a cigarette's CO?COHb was lower after switching in 9 trials, all tobacco-funded: about half lower overall, about a fifth with 4+ weeks' follow-up (our back-calculation). A marker; no exercise tested.Main caveat: All 11 RCTs were funded by tobacco companies; no independent replication; publication bias not ruled out by the authors.Tattan-Birch 2022

Is nicotine riskier in the heat?In 10 nicotine-naive trained men, an overnight 7-mg patch raised core temperature more at 30 °C and blunted skin blood flow; 2 could not finish. No measured power effect. From the abstract.Main caveat: Abstract only; the saved source is the PubMed record.Moyen 2024

Is hookah CO gone by the next morning?In 32 students exhaled CO ran about 7.5-fold a cigarette session's level indoors and was still raised 10 h after, size not given. A marker, not performance. From the abstract.Main caveat: Abstract only; no absolute exhaled CO values, no size for the 10-h rise, no comparator named for it.Juhasz 2017

How much CO does one hookah session put in the blood?In 47 young adults, COHb rose from 2.0% to 17.6% after 30 min indoors; passive sitters 0.8% to 1.2%. A marker, no exercise tested. From the abstract.Main caveat: Abstract only; the unclear ">25%" and ">40%" figures could not be checked against the paper.Bentur 2014

How often must I heat-train to keep acclimation?Twice a week, in one small RCT of 24 trained men: after 8 weeks, heart rate in the heat was 151 vs 174 bpm with no heat training. Once a week: no clear difference from none.Main caveat: Abstract only: group sizes, how acclimatisation and acclimation were done, acclimated heart rate and rectal temperature, the training groups'…Benjamin 2022

Will I lose my heat acclimation in the taper?Some: about 2.5% of the heart-rate and core-temperature gain per day without heat, and re-exposure brings it back fast. From 12 small studies, mostly in fit young men.Main caveat: Small, old, heterogeneous studies. The analysed studies had 6 to about 24 participants, the review includes six early studies, and the protocols used walking…Daanen 2018

Policy statement — Climatic heat stress and exercising children and adolescents (American Academy of Pediatrics): contrary to previous thinking, youth do not thermoregulate worse, have less cardiovascular capacity or tolerate exertion less than adults in the heat when adequately hydrated; the main risks are poor hydration, undue exertion, too little recovery between bouts or same-day sessions, and heat-retaining clothing and equipment — all modifiable, so exertional heat illness is usually preventableMain caveat: Policy statement; the abstract does not describe how the evidence was searched or graded.Bergeron 2011

Rain at 5 °C makes even hard running colder and costlier: rectal temperature was lower from 10 minutes, and oxygen uptake and perceived exertion were higher by 50–60 minutesMain caveat: Small, young fit men, 5 °C only; performance was not measured. Abstract only was read.Ito 2019

In a thin full-body race suit with a 5 m/s wind, hard running was best at −4 to +1 °C and already impaired at +10 °CThe best temperature depends on what is wornMain caveat: N = 9 trained men, short treadmill protocol, one garment. Abstract only was read.Sandsund 2012

At about 70% VO2max in still air, cycling time to exhaustion was longest at 10.5 °C (93.5 min) and shortest at 30.5 °C (51.6 min)An inverted U with temperatureMain caveat: N = 8, time to exhaustion rather than a time trial, clothing not stated in the abstract. Abstract only was read.Galloway & Maughan 1997

Marathon performance slows progressively as WBGT rises from 5 to 25 °CTop men were 1.7% off the course record in the 5–10 °C band and 4.5% off at 20–25 °C — and slower runners lose moreMain caveat: WBGT, not air temperature; nothing below 5 °C; the differences for top women were not significant. Abstract only was read.Ely 2007

Across 1.79 million marathon performances the air temperature for the fastest running was 3.8–9.9 °C depending on level; performance fell on both sides, and withdrawals rose with heatMain caveat: Race-level temperature against the speed distribution, with modest fits (r² 0.24–0.27 in the examples shown); wind was not analysed.El Helou 2012

Defining the "dose" of altitude training: how high to live for optimal sea level performance enhancementMain caveat: No sea-level control group: a training-camp effect cannot be separated from the altitude effect.Chapman 2014

Pre-Altitude Serum Ferritin Levels and Daily Oral Iron Supplement Dose Mediate Iron Parameter and Hemoglobin Mass Responses to Altitude ExposureMain caveat: Retrospective and observational: iron dose was not randomised, so athletes given more iron may have differed in iron status or in other ways.Govus 2015

One hour of internal precooling with cold water/menthol enhances cycling performance in a heat/wet stress environment: A pilot studyMain caveat: A pilot with n=7, men only, all heat-acclimated; randomisation and blinding not stated in the abstract.Rinaldi 2023

Physical and Perceptual Cooling with Beverages to Increase Cycle Performance in a Tropical ClimateMain caveat: n=12, men only; randomisation and blinding not stated in the abstract (drink temperature and a menthol aroma cannot be hidden from the rider).Riera 2014

Perceptual, Thermoregulatory, and Performance Effects of Menthol Gel Application in Trained Triathletes Exercising in Hot ConditionsMain caveat: n=8; sex not stated; no blinding possible with gel vs no gel, and no placebo gel.Barwood 2025

Enhancement of Exercise Capacity in the Heat With Repeated Menthol-Spray ApplicationMain caveat: n=8; sex not stated; randomisation and blinding not stated in the abstract (a menthol spray is hard to blind).Barwood 2019

Effects of different menthol administration routes on endurance performance and physiological responses in the heat: a network meta-analysisMain caveat: Most pairwise comparisons were not significant; SUCRA values rank the routes without showing that any differs from another or from control.Zhu 2026

Acute topical menthol application and exercise performance: A systematic review and meta-analysis of perceptual and physiological responsesMain caveat: Sixteen studies and 191 participants in total — small trials; several subgroup results were sensitive to influential observations.Wang 2026

How Cool is That? The Effects of Menthol Mouth Rinsing on Exercise Capacity and Performance: A Systematic Review and Meta-analysisMain caveat: Ten studies; participant numbers and trial designs are not in the abstract.Gavel 2024

The effects of menthol on exercise performance and thermal sensation: A meta-analysisMain caveat: Thirteen articles; participant numbers, trial designs and conditions are not in the abstract, and all routes and test types are pooled.Jeffries & Waldron 2019

Five days of heat acclimation is not enough to raise the critical environmental limitNine are; and the drop in core-temperature rise appears only after 4-8 days of recovery, not during the blockMain caveat: Population is occupational, not athletic: non-acclimatized participants in a study designed for occupational safety guidelines.van den Bogaard 2025

Chronic pill use impairs the sweating response in the heatThe sudomotor threshold and thermosensitivity are both blunted versus naturally cycling athletes, so an athlete on the pill is not simply "a cycle that got standardised"Main caveat: n = 10, combined monophasic pills only, well-trained women. Small, and one class of drug among many.Lei 2019

Sex differences in sweating appear only above a high heat-loss requirement, come from sweat gland OUTPUT rather than gland recruitmentAnd there is no sex difference in skin blood flowMain caveat: n=16 (8 per sex), acute laboratory exposure. Small. Training status and age are not given in the abstract.Gagnon & Kenny 2012

In well-trained women, cycle phase did NOT affect performance in the heatHumidity did, costing 7% of work doneMain caveat: n=10. A null result in a sample this small is weak evidence of no effect; it cannot exclude a small phase effect.Lei 2017

Menstrual cycle phase cost endurance performance in hot, humid conditions but not in temperate onesThe environment decides whether the cycle shows up at allMain caveat: Small (12 tested per condition, n = 8 in each analysis) and recreationally active.Janse de Jonge 2012

The luteal phase raises core temperature before and throughout exercise in the heatBut sweat rate, skin temperature and exercise heart rate do not differ between cycle phasesMain caveat: Only 9 studies and 83 participants pooled. The authors themselves call the data limited.Giersch 2020

The spread in altitude losses is not random: the higher the sea-level VO₂max and lactate threshold, the LARGER the decline at a simulated 3000 mThe fittest athletes lose the mostMain caveat: n=12, published 1995, mixed sample (ice-hockey players plus skiers, men and women pooled). Very small.Koistinen 1995

Aerobic performance declines LINEARLY with altitudeAbout −6.3% VO₂max per 1000 m — and the loss is already statistically significant at 800 m: there is no threshold below which altitude is freeMain caveat: n=8, running, acute exposure, single laboratory, 2006. There was no acclimatization at all — the slope describes a first encounter with altitude, not the state…Wehrlin & Hallén 2006

Daytime napping in athletes — systematic review of 37 studies: naps may benefit physical and cognitive performance, perception, psychological state and night sleep; 20-90 min between 13:00 and 16:00, with 30 min to clear sleep inertia before trainingMain caveat: SR without meta-analysis of 37 mostly small, heterogeneous studies of moderate quality; most did not report nap frequency, duration or timing consistently.Lastella 2021

Physical & cognitive performance vary with time of day AND chronotype"night owls" are impaired in the morning on every measure vs early typesMain caveat: Healthy volunteers not elites; lab tasks not competition; only three test times; effect sizes vary by task/chronotype extremity.Facer-Childs 2018

Managing travel fatigue and jet lag in athletes: review & consensus statement (26-expert panel)Main caveat: Consensus statement; the panel explicitly notes that the lack of evidence restricts the strength of its recommendations.Janse van Rensburg 2021

The Effects of Palmar Cooling on Repeated Sprinting Ability: A Randomized Controlled Clinical TrialMain caveat: Small sample (n=15, two groups of ~7-8) — the authors call for a larger sample before generalisingBrown M 2025