This article focuses on studies that relate running performance and physical duress in tropical climates, specifically: running in humidity. Just like in Singapore, Hong Kong, Shanghai or New York in the summertime.
What is humidity and why does it matter?
Absolute humidity measures of the amount of water vapour in the air (moisture), regardless of the air's temperature. This is usually measured in grams per cubic meter.
Relative humidity compares the amount of water vapour present in the air relative to the amount of water vapour the air can hold at a given temperature. This is expressed as a percentage and indicates how close the air is to being saturated with moisture.
High relative humidity can make it feel hotter because our bodies rely on sweat evaporation to cool down. When the air is saturated with moisture, sweat doesn't evaporate as efficiently. Exercising in hot and humid conditions makes workouts feel more challenging, increases heart rate, the risk of dehydration and decreases performance.
In these conditions it is prudent to stay hydrated without over-hydrating, modify exercise intensity as needed and to recover properly.
Click on the links in the studies below to be taken to the relevant papers. If you have other studies to share, let us have them in the Comments at bottom of page. Include the citation and/or PMID if possible. Hyponatremia, exertional heat stress, thermoregulation and heat acclimation we will focus on elsewhere, although these issues are described in some of the studies we share.
Please note, these resources are shared for information purposes only. Always seek appropriate assistance for heat related medical situations, they can be life threatening. If you are considering changing your diet, exercise or lifestyle practices, discuss plans with your primary medical practitioner before making any changes; especially if you are under treatment.
Hydrate, Sweat, Repeat
Alastair
The following articles might also be of value...
Performance in Humid Conditions
Jenkins EJ, Campbell HA, Lee JKW, Mündel T, Cotter JD. Delineating the impacts of air temperature and humidity for endurance exercise. Exp Physiol. 2023 Feb;108(2):207-220. doi: 10.1113/EP090969. Epub 2022 Dec 20. PMID: 36537856; PMCID: PMC10103870.
Alkemade P, DE Korte JQ, Bongers CCWG, Daanen HAM, Hopman MTE, Janssen TWJ, Eijsvogels TMH. Humid Heat Equally Impairs Maximal Exercise Performance in Elite Para-Athletes and Able-Bodied Athletes. Med Sci Sports Exerc. 2023 Oct 1;55(10):1835-1844. doi: 10.1249/MSS.0000000000003222. Epub 2023 May 22. PMID: 37227231; PMCID: PMC10487364.
Mantzios K, Ioannou LG, Panagiotaki Z, Ziaka S, Périard JD, Racinais S, Nybo L, Flouris AD. Effects of Weather Parameters on Endurance Running Performance: Discipline-specific Analysis of 1258 Races. Med Sci Sports Exerc. 2022 Jan 1;54(1):153-161. doi: 10.1249/MSS.0000000000002769. PMID: 34652333; PMCID: PMC8677617.
Weiss, K., Valero, D., Villiger, E. et al. Relationship between running performance and weather in elite marathoners competing in the New York City Marathon. Sci Rep 12, 21264 (2022). https://doi.org/10.1038/s41598-022-25901-z
Weiss K, Valero D, Villiger E, Scheer V, Thuany M, Cuk I, Rosemann T, Knechtle B. The Influence of Environmental Conditions on Pacing in Age Group Marathoners Competing in the "New York City Marathon". Front Physiol. 2022 Jun 14;13:842935. doi: 10.3389/fphys.2022.842935. PMID: 35774288; PMCID: PMC9237513.
Xu Y, Zhao Y, Gao B. Effects of hot and humid environments on thermoregulation and aerobic endurance capacity of Laser sailors. J Exerc Sci Fit. 2022 Oct;20(4):283-290. doi: 10.1016/j.jesf.2022.06.003. Epub 2022 Jun 23. PMID: 35812826; PMCID: PMC9256823.
Vecellio DJ, Wolf ST, Cottle RM, Kenney WL. Evaluating the 35°C wet-bulb temperature adaptability threshold for young, healthy subjects (PSU HEAT Project). J Appl Physiol (1985). 2022 Feb 1;132(2):340-345. doi: 10.1152/japplphysiol.00738.2021. Epub 2021 Dec 16. PMID: 34913738; PMCID: PMC8799385.
Tan XR, Low ICC, Byrne C, Wang R, Lee JKW. Assessment of dehydration using body mass changes of elite marathoners in the tropics. J Sci Med Sport. 2021 Aug;24(8):806-810. doi: 10.1016/j.jsams.2021.01.008. Epub 2021 Jan 31. PMID: 33573872.
Baillot M, Hue O, Tran TT, Antoine-Jonville S. Neuromuscular Activity during Cycling Performance in Hot/Dry and Hot/Humid Conditions. Life (Basel). 2021 Oct 28;11(11):1149. doi: 10.3390/life11111149. PMID: 34833025; PMCID: PMC8623245.
Lei TH, Wang F. Looking ahead of 2021 Tokyo Summer Olympic Games: How Does Humid Heat Affect Endurance Performance? Insight into physiological mechanism and heat-related illness prevention strategies. J Therm Biol. 2021 Jul;99:102975. doi: 10.1016/j.jtherbio.2021.102975. Epub 2021 Apr 22. PMID: 34420619.
Rivera-Brown AM, Quiñones-González JR. Normative Data for Sweat Rate and Whole-Body Sodium Concentration in Athletes Indigenous to Tropical Climate. Int J Sport Nutr Exerc Metab. 2020 Jul 1;30(4):264-271. doi: 10.1123/ijsnem.2019-0299. Epub 2020 May 25. PMID: 32454460.
Rodrigues Júnior JFC, Mckenna Z, Amorim FT, Da Costa Sena AF, Mendes TT, Veneroso CE, Torres Cabido CE, Sevilio De Oliveira Júnior MN. Thermoregulatory and metabolic responses to a half-marathon run in hot, humid conditions. J Therm Biol. 2020 Oct;93:102734. doi: 10.1016/j.jtherbio.2020.102734. Epub 2020 Sep 15. PMID: 33077145.
Hermand E, Chabert C, Hue O. Ultra-endurance events in tropical environments and countermeasures to optimize performances and health. Int J Hyperthermia. 2019;36(1):753-760. doi: 10.1080/02656736.2019.1635718. PMID: 31429600.
Notley SR, Poirier MP, Hardcastle SG, Flouris AD, Boulay P, Sigal RJ, Kenny GP. Aging Impairs Whole-Body Heat Loss in Women under Both Dry and Humid Heat Stress. Med Sci Sports Exerc. 2017 Nov;49(11):2324-2332. doi: 10.1249/MSS.0000000000001342. PMID: 29045327.
Che Muhamed AM, Atkins K, Stannard SR, Mündel T, Thompson MW. The effects of a systematic increase in relative humidity on thermoregulatory and circulatory responses during prolonged running exercise in the heat. Temperature (Austin). 2016 May 18;3(3):455-464. doi: 10.1080/23328940.2016.1182669. PMID: 28349085; PMCID: PMC5079215.
Cooper ER, Ferrara MS, Casa DJ, Powell JW, Broglio SP, Resch JE, Courson RW. Exertional Heat Illness in American Football Players: When Is the Risk Greatest? J Athl Train. 2016 Aug;51(8):593-600. doi: 10.4085/1062-6050-51.8.08. Epub 2016 Aug 9. PMID: 27505271; PMCID: PMC5094838.
Maughan RJ, Otani H, Watson P. Influence of relative humidity on prolonged exercise capacity in a warm environment. Eur J Appl Physiol. 2012 Jun;112(6):2313-21. doi: 10.1007/s00421-011-2206-7. Epub 2011 Oct 20. PMID: 22012542.
Hydration and Nutrition Studies
Pałka, T.; Rydzik, Ł.; Koteja, P.M.; Piotrowska, A.; Bagińska, M.; Ambroży, T.; Angelova-Igova, B.; Javdaneh, N.; Wiecha, S.; Filip-Stachnik, A.; et al. Effect of Various Hydration Strategies on Work Intensity and Selected Physiological Indices in Young Male Athletes during Prolonged Physical Exercise at High Ambient Temperatures. J. Clin. Med. 2024, 13, 982. https://doi.org/10.3390/jcm13040982
Choo HC, Choo DHW, Tan I, Chang J, Chow KM, Lee JKW, Burns SF, Ihsan M. Effect of ice slurry ingestion on thermoregulatory responses during fixed-intensity cycling in humid and dry heat. Eur J Appl Physiol. 2023 Oct;123(10):2225-2237. doi: 10.1007/s00421-023-05235-y. Epub 2023 May 31. PMID: 37256293.
Wijering LAJ, Cotter JD, Rehrer NJ. A randomized, cross-over trial assessing effects of beverage sodium concentration on plasma sodium concentration and plasma volume during prolonged exercise in the heat. Eur J Appl Physiol. 2023 Jan;123(1):81-89. doi: 10.1007/s00421-022-05025-y. Epub 2022 Sep 29. PMID: 36173481; PMCID: PMC9813217.
Jardine WT, Aisbett B, Kelly MK, Burke LM, Ross ML, Condo D, Périard JD, Carr AJ. The Effect of Pre-Exercise Hyperhydration on Exercise Performance, Physiological Outcomes and Gastrointestinal Symptoms: A Systematic Review. Sports Med. 2023 Nov;53(11):2111-2134. doi: 10.1007/s40279-023-01885-2. Epub 2023 Jul 25. PMID: 37490269; PMCID: PMC10587316.
Alhadad SB, Chua MCY, Lee JKW, Low ICC. The effects of low and normal dose ice slurry ingestion on endurance capacity and intestinal epithelial injury in the heat. J Sci Med Sport. 2023 Jun;26(6):278-284. doi: 10.1016/j.jsams.2023.04.008. Epub 2023 Apr 29. PMID: 37179242.
Ly NQ, Hamstra-Wright KL, Horswill CA. Post-Exercise Rehydration in Athletes: Effects of Sodium and Carbohydrate in Commercial Hydration Beverages. Nutrients. 2023 Nov 12;15(22):4759. doi: 10.3390/nu15224759. PMID: 38004153; PMCID: PMC10674530.
Choo HC, Choo DHW, Tan I, Chang J, Chow KM, Lee JKW, Burns SF, Ihsan M. Effect of ice slurry ingestion on thermoregulatory responses during fixed-intensity cycling in humid and dry heat. Eur J Appl Physiol. 2023 Oct;123(10):2225-2237. doi: 10.1007/s00421-023-05235-y. Epub 2023 May 31. PMID: 37256293.
Veniamakis E, Kaplanis G, Voulgaris P, Nikolaidis PT. Effects of Sodium Intake on Health and Performance in Endurance and Ultra-Endurance Sports. Int J Environ Res Public Health. 2022 Mar 19;19(6):3651. doi: 10.3390/ijerph19063651. PMID: 35329337; PMCID: PMC8955583.
Surapongchai J, Saengsirisuwan V, Rollo I, Randell RK, Nithitsuttibuta K, Sainiyom P, Leow CHW, Lee JKW. Hydration Status, Fluid Intake, Sweat Rate, and Sweat Sodium Concentration in Recreational Tropical Native Runners. Nutrients. 2021 Apr 20;13(4):1374. doi: 10.3390/nu13041374. PMID: 33923890; PMCID: PMC8072971.
Alhadad SB, Low ICC, Lee JKW. Thermoregulatory responses to ice slurry ingestion during low and moderate intensity exercises with restrictive heat loss. J Sci Med Sport. 2021 Jan;24(1):105-109. doi: 10.1016/j.jsams.2020.07.002. Epub 2020 Jul 15. PMID: 32711957.
McCubbin AJ, Allanson BA, Caldwell Odgers JN, Cort MM, Costa RJS, Cox GR, Crawshay ST, Desbrow B, Freney EG, Gaskell SK, Hughes D, Irwin C, Jay O, Lalor BJ, Ross MLR, Shaw G, Périard JD, Burke LM. Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments. Int J Sport Nutr Exerc Metab. 2020 Jan 1;30(1):83-98. doi: 10.1123/ijsnem.2019-0300. PMID: 31891914.
Che Muhamed AM, Yusof HA, Stannard SR, Mündel T, Thompson MW. The Efficacy of Ingesting Water on Thermoregulatory Responses and Running Performance in a Warm-Humid Condition. Front Physiol. 2019 May 7;10:507. doi: 10.3389/fphys.2019.00507. PMID: 31133869; PMCID: PMC6514147.
Hanson NJ, Martinez SC, Byl EN, Maceri RM, Miller MG. Increased Rate of Heat Storage, and No Performance Benefits, With Caffeine Ingestion Before a 10-km Run in Hot, Humid Conditions. Int J Sports Physiol Perform. 2019 Feb 1;14(2):196-202. doi: 10.1123/ijspp.2018-0263. Epub 2019 Jan 3. PMID: 30039995.
Kenefick RW. Drinking Strategies: Planned Drinking Versus Drinking to Thirst. Sports Med. 2018 Mar;48(Suppl 1):31-37. doi: 10.1007/s40279-017-0844-6. PMID: 29368181; PMCID: PMC5790864.
McDermott BP, Anderson SA, Armstrong LE, Casa DJ, Cheuvront SN, Cooper L, Kenney WL, O'Connor FG, Roberts WO. National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active. J Athl Train. 2017 Sep;52(9):877-895. doi: 10.4085/1062-6050-52.9.02. PMID: 28985128; PMCID: PMC5634236.
Nolte HW, Nolte K, van der Meulen J. Total Body Water, Electrolyte, and Thermoregulatory Responses to Ad Libitum Water Replacement Using Two Different Water Delivery Systems During a 19-km Route March. J Strength Cond Res. 2015 Nov;29 Suppl 11:S88-93. doi: 10.1519/JSC.0000000000001028. PMID: 26506205.
Johannsen NM, Lind E, King DS, Sharp RL. Effect of preexercise electrolyte ingestion on fluid balance in men and women. Med Sci Sports Exerc. 2009 Nov;41(11):2017-25. doi: 10.1249/MSS.0b013e3181a82940. PMID: 19812516.
Other
Tan XR, Low ICC, Byrne C, Wang R, Lee JKW. Assessment of dehydration using body mass changes of elite marathoners in the tropics. J Sci Med Sport. 2021 Aug;24(8):806-810. doi: 10.1016/j.jsams.2021.01.008. Epub 2021 Jan 31. PMID: 33573872.
Tyler CJ, Reeve T, Hodges GJ, Cheung SS. The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis. Sports Med. 2016 Nov;46(11):1699-1724. doi: 10.1007/s40279-016-0538-5. Erratum in: Sports Med. 2016 Nov;46(11):1771. PMID: 27106556.
Resources
Weather and Heat Stress. Singapore provides live heat stress information, stay up-to-date here.
Learn about Singapore's Heat Resilience and Performance Centre (HRPC) at the Yong Loo Lin School of Medicine, NUS Medicine.
From the USA, The Warrior Heat- and Exertion-Related Events Collaborative (WHEC) Heat Illness Resources WHEC is a multidisciplinary advisory group focused on developing and implementing procedures to help providers, service members and civilians prevent and treat heat-related illnesses and injuries. WHEC works in collaboration with the Army Heat Center (Fort Moore, GA) and the Uniformed Services University's Multidisciplinary Case Review Committee.
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