Mixed-Method Heat Acclimation Induces Heat Adaptations in International Triathletes Without Training Modification

Abstract

Purpose

Heat acclimation (HA) kinetics often necessitates that the intervention is conducted in the weeks immediately preceding athletic competitions, potentially interfering with a training taper. Therefore, we investigated the efficacy of a mixed-method HA protocol, superimposed over planned external training loads, during the 3-weeks prior to the 2022 U23 World Triathlon Championships.

Methods

Six international triathletes completed 8 pre-competition HA sessions (5 active: running/cycling, 3 passive: hot water immersion [HWI]), across 2-weeks. Outdoor high-intensity training sessions were followed by 30–60 min HWI, whilst low-intensity cycling/running sessions were completed in a hot, humid environmental chamber. To assess heat adaptations, participants completed three 25 min heat stress tests (HST) involving iso-speed treadmill running (session 1 = HST1, session 5 = HST2, and session 8 = HST3). Physiological, haematological and wellbeing monitoring were conducted throughout HA.

Results

Reduced heart rate (~ − 6 beats/min) was observed within HST3 (P = 0.01, η _p ² = 0.64), versus HST1 and HST2. No changes in core temperature were observed across HSTs (P = 0.055, η _p ² = 0.44). Sweat sodium concentration was lower by HST2 at the arm (− 23 ± 16 mmol/L, P = 0.02) and back (− 27 ± 17 mmol/L, P = 0.01). White blood cell count reduced from baseline to the end of HA (P = 0.02, η _p ² = 0.27), but no changes were found in any other haematological markers (all P > 0.05). Perceptual wellbeing measures did not change across HA (all P > 0.05).

Conclusion

By HST3, seven prior mixed-method HA sessions improved markers of heat adaptation (exercising HR and sweat concentration) within international triathletes. Mixed-method HA may be implemented without modifying training load, with no apparent detrimental effects on athlete health or training stress markers.

Keywords

Adaptation / Endurance / Performance / Thermoregulation / Triathlon

References

[1.] Akubat I, Taylor AR, Sanders D, Myers T, Abt G, Taylor C. The dose-response relationship between training load and aerobic fitness in academy rugby union players. Int J Sports Physiol Performance, 2017, 13(2): 163-169

[2.] Altman DG, Bland JM. Measurement in medicine: the analysis of method comparison studies. J R Stat Soc Ser D (The Stat), 1983, 32(3): 307-317,

[3.] Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet, 1986, 327(8476): 307-310,

[4.] Borg G, Löllgen H. Borg’s perceived exertion and pain scales. Dtsch Z Sportmed, 2001, 52(9): 252

[5.] Buono MJ, Kolding M, Leslie E, Moreno D, Norwood S, Ordille A, Weller R. Heat acclimation causes a linear decrease in sweat sodium ion concentration. J Thermal Biol, 2018, 71: 237-240,

[6.] Casadio JR, Kilding AE, Cotter JD, Laursen PB. From lab to real world: heat acclimation considerations for elite athletes. Sports Med, 2016, 47(8): 1467-1476,

[7.] Cejuela R, Esteve-Lanao J. Training load quantification in triathlon. J Hum Sport Exerc, 2011, 6(2): 218-232,

[8.] Cejuela R, Sellés-Pérez S. Road to Tokyo 2020 olympic games: training characteristics of a world class male triathlete. Front Physiol, 2022, 13(April): 1-10,

[9.] Chinevere TD, Kenefick RW, Cheuvront SN, Lukaski HC, Sawka MN. Effect of heat acclimation on sweat minerals. Med Sci Sports Exer, 2008, 40(5): 886-891,

[10.] Costello JT, Rendell RA, Furber MJW, Massey HC, Tipton MJ, Young JS, Corbett J. Effects of acute or chronic heat exposure, exercise and dehydration on plasma cortisol, IL-6 and CRP levels in trained males. Cytokine, 2018, 110: 277-283,

[11.] Daanen HAM, Racinais S, Périard JD. Heat acclimation decay and re-induction: a systematic review and meta-analysis. Sports Med, 2018, 48(2): 409-430,

[12.] Dill DB, Costill DL. Calculation of percentage changes in volumes of blood, plasma, and red cells in dehydration. J Appl Physiol (Bethesda, Md), 1985, 37(2): 247-248

[13.] Fox RH, Goldsmith R, Kidd DJ, Lewis HE. Acclimatization to heat in man by controlled elevation of body temperature. J Physiol, 1963, 166(3): 530-547, pmcid: 1359351,

[14.] Gagge A, Stolwijk J, Saltin B. Comfort and thermal sensations and associated physiological responses during exercise at various ambient temperatures. Environ Res, 1969, 2(3): 209-229,

[15.] Galan-Lopez N, et al.. Heat preparation and knowledge at the world athletics race walking team championships muscat. Int J Sports Physiol Performance, 2023, 18(8): 813-824,

[16.] Gibson OR, James CA, Mee JA, Willmott AGB, Turner G, Hayes M, Maxwell NS. Heat alleviation strategies for athletic performance: a review and practitioner guidelines. Temperature, 2019, 7(1): 3-36,

[17.] Gibson OR, Mee JA, Tuttle JA, Taylor L, Watt PW, Maxwell NS. Isothermic and fixed intensity heat acclimation methods induce similar heat adaptation following short and long-term timescales. J Therm Biol, 2015, 49–50: 55-65,

[18.] Gibson OR, Willmott AGB, James CA, Hayes M, Maxwell NS. Power relative to body mass best predicts change in core temperature during exercise-heat stress. J Strength Condition Res, 2017, 31(2): 403-414,

[19.] Gleeson M. Biochemical and immunological markers of overtraining. J Sports Sci Med, 2002, 1(2): 31-41, pmcid: 3963240,

[20.] Guy JH, Pyne DB, Deakin GB, Miller CM, Edwards AM. Acclimation training improves endurance cycling performance in the heat without inducing endotoxemia. Front Physiol, 2016, 7: 318, pmcid: 4965461,

[21.] Hailes WS, Slivka D, Cuddy J, Ruby BC. Human plasma inflammatory response during 5 days of exercise training in the heat. J Thermal Biol, 2011, 5(36): 277-282,

[22.] Heathcote SL, Hassmén P, Zhou S, Stevens CJ. Passive heating: reviewing practical heat acclimation strategies for endurance athletes. Front Physiol, 2018, 9: 1851, pmcid: 6306444,

[23.] Henderson MJ, Chrismas BCR, Stevens CJ, Novak A, Fransen J, Coutts AJ, Taylor L. Additional clothing increases heat load in elite female Rugby sevens players. Int J Sports Physiol Perform, 2021, 16(10): 1424-1431,

[24.] Horn PL, Pyne DB, Hopkins WG, Barnes CJ. Lower white blood cell counts in elite athletes training for highly aerobic sports. Eur J Appl Physiol, 2010, 110(5): 925-932,

[25.] Impellizzeri FM, Marcora SM, Coutts AJ. Internal and external training load: 15 years on. Int J Sports Physiol Perform, 2019, 14(2): 270-273,

[26.] James CA, Dhawan A, Jones T, Pok C, Yeo V, Girard O. Minimal agreement between internal and external training load metrics across a 2-wk training microcycle in elite squash. J Sports Sci Med, 2021, 20(1): 101-109, pmcid: 7919364,

[27.] James CA, Hayes M, Willmott AGB, Gibson OR, Flouris AD, Schlader ZJ, Maxwell NS. Defining the determinants of endurance running performance in the heat. Temperature, 2017, 4(3): 314-329,

[28.] James CA, Richardson AJ, Watt PW, Maxwell NS. Reliability and validity of skin temperature measurement by telemetry thermistors and a thermal camera during exercise in the heat. J Thermal Biol, 2014, 45: 141-149,

[29.] James CA, Richardson AJ, Watt PW. Physiological responses to incremental exercise in the heat following internal and external precooling. Scand J Med Sci Sports, 2015, 25(s1): 190-199,

[30.] James CA, Richardson AJ, Watt PW, Willmott AGB, Gibson OR, Maxwell NS. Short-term heat acclimation and precooling, independently and combined, improve 5-km time trial performance in the heat. J Strength Condition Res, 2018, 32(5): 1366-1375,

[31.] James CA, Richardson AJ, Willmott AGB, Watt PW, Gibson OR, Maxwell NS. Short-term heat acclimation improves the determinants of endurance performance and 5-km running performance in the heat. Appl Physiol Nutrit Metab, 2017, 42(3): 285-294,

[32.] James CA, Willmott AGB, Dhawan A, Stewart C, Gibson OR. Increased air temperature decreases high-speed, but not total distance, in international field hockey. Temperature, 2021, 9(4): 357-372,

[33.] Kanikowska D, Sato M, Sugenoya J, Iwase S, Shimizu Y, Nishimura N, Inukai Y. No effects of acclimation to heat on immune and hormonal responses to passive heating in healthy volunteers. Int J Biometeorol, 2012, 56(1): 107-112,

[34.] Kirby NV, Lucas SJE, Armstrong OJ, Weaver SR, Lucas RAI. Intermittent post-exercise sauna bathing improves markers of exercise capacity in hot and temperate conditions in trained middle-distance runners. Eur J Appl Physiol, 2021, 121(2): 621-635,

[35.] Kirby NV, Lucas SJE, Lucas RAI. Nine-, but not four-days heat acclimation improves self-paced endurance performance in females. Front Physiol, 2019, 10: 1-12,

[36.] Klous L, De Ruiter R, Alkemade P, Daanen H, Gerrett N. Sweat rate and sweat composition during heat acclimation. J Thermal Biol, 2020, 93,

[37.] Lorenzo S, Halliwill JR, Sawka MN, Minson CT. Heat acclimation improves exercise performance. J Appl Physiol (1985), 2010, 109(4): 1140-1147,

[38.] Lundby C, Hamarsland H, Hansen J, Bjørndal H, Berge SN, Hammarström D, Rønnestad BR. Hematological, skeletal muscle fiber and exercise performance adaptations to heat training in elite female and male cyclists. J Appl Physiol, 2023, 135(1): 217-226,

[39.] Mackinnon LT. Special feature for the Olympics: effects of exercise on the immune system: overtraining effects on immunity and performance in athletes. Immunol Cell Biol, 2000, 78(5): 502-509,

[40.] McIntyre RD, Zurawlew MJ, Mee JA, Walsh NP, Oliver SJ. A comparison of medium-term heat acclimation by post-exercise hot water immersion or exercise in the heat: Adaptations, overreaching, and thyroid hormones. Am J Physiol Regul Integr Comp Physiol, 2022, 323(5): R601-R615, pmcid: 9602919,

[41.] McKay AKA, Stellingwerff T, Smith ES, Martin DT, Mujika I, Goosey-Tolfrey VL, Sheppard J, Burke LM. Defining training and performance caliber: a participant classification framework. Int J Sports Physiol Perform, 2022, 17(2): 317-331,

[42.] Mitchell JB, Dugas JP, McFarlin BK, Nelson MJ. Effect of exercise, heat stress, and hydration on immune cell number and function. Med Sci Sports Exerc, 2002, 34(12): 1941-1950,

[43.] Mujika I. Tapering for triathlon competition. J Hum Sport Exerc, 2011, 6(2): 264-270,

[44.] Mujika I. Olympic preparation of a world-class female triathlete. Int J Sports Physiol Perform, 2014, 9(4): 727-731,

[45.] Mujika I, Halson S, Burke LM, Balagué G, Farrow D. An integrated, multifactorial approach to periodization for optimal performance in individual and team sports. Int J Sports Physiol Perform, 2018, 13(5): 538-561,

[46.] Murray NB, Gabbett TJ, Townshend AD, Blanch P. Calculating acute:chronic workload ratios using exponentially weighted moving averages provides a more sensitive indicator of injury likelihood than rolling averages. Br J Sports Med, 2017, 51(9): 749-754,

[47.] National Oceanic and Atmospheric Administration. Integrated Surface Database – Ipoh, Perak, Malaysia historical data. 2023. https://www.wunderground.com/. Accessed 20 Oct 2023.

[48.] Périard JD, Racinais S, Timpka T, Dahlström Ö, Spreco A, Jacobsson J, Bargoria V, Halje K, Alonso JM. Strategies and factors associated with preparing for competing in the heat: a cohort study at the 2015 IAAF World Athletics Championships. Br J Sports Med, 2017, 51(4): 264-270,

[49.] Périard JD, Eijsvogels TMH, Daanen HAM. Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies. Physiol Rev, 2021, 101(4): 1873-1979,

[50.] Pryor JL, Johnson EC, Roberts WO, andPryor, R.R. . Application of evidence-based recommendations for heat acclimation: Individual and team sport perspectives. Temperature, 2019, 6(1): 37-49,

[51.] Ramos JAP, Brade CJ, Ducker KJ, Landers GJ, Girard O. The internal-to-external load ratio: a tool to determine the efficacy of heat acclimation/acclimatization using self-paced exercise. Front Sports Active Living, 2022, 3: 2021-2023,

[52.] Ruddock AD, Thompson SW, Hudson SA, James CA, Gibson OR, Mee JA. Combined active and passive heat exposure induced heat acclimation in a soccer referee before 2014 FIFA World Cup. Springerplus, 2016, 5(1): 617, pmcid: 4870546,

[53.] Sawka MN, Leon LR, Montain SJ, Sonna LA. Integrated physiological mechanisms of exercise performance, adaptation, and maladaptation to heat stress. Comprehensive Physiol, 2011, 1(4): 1883-1928,

[54.] Stanley J, Halliday A, D’Auria S, Buchheit M, Leicht AS. Effect of sauna-based heat acclimation on plasma volume and heart rate variability. Eur J Appl Physiol, 2015, 115(4): 785-794,

[55.] Stephenson BT, Tolfrey K, Goosey-Tolfrey VL. Mixed active and passive heart rate-controlled heat acclimation is effective for paralympic and able-bodied triathletes. Front Physiol, 2019, 10: 1214, pmcid: 6763681,

[56.] 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, 46(11): 1699-1724,

[57.] Wilkinson DM, Carter JM, Richmond VL, Blacker SD, Rayson MP. The effect of cool water ingestion on gastrointestinal pill temperature. Med Sci Sports Exerc, 2008, 40(3): 523-528,

[58.] Willmott AGB, et al.. Short-term heat acclimation prior to a multi-day desert ultra-marathon improves physiological and psychological responses without compromising immune status. J Sports Sci, 2017, 35(22): 2249-2256,

[59.] Willmott AGB, Gibson OR, Hayes M, Maxwell NS. The effects of single versus twice daily short term heat acclimation on heat strain and 3000m running performance in hot, humid conditions. J Thermal Biol, 2016, 56: 59-67,

[60.] Willmott AGB, Gibson OR, James CA, Hayes M, Maxwell NS. Physiological and perceptual responses to exercising in restrictive heat loss attire with use of an upper-body sauna suit in temperate and hot conditions. Temperature, 2018, 5(2): 162-174,

[61.] Willmott AGB, Hayes M, Dekerle J, Maxwell NS. The reliability of a heat acclimation state test prescribed from metabolic heat production intensities. J Thermal Biol, 2015, 53: 38-45,

[62.] Willmott AGB, Hayes M, James CA, Dekerle J, Gibson OR, Maxwell NS. Once- and twice-daily heat acclimation confer similar heat adaptations, inflammatory responses and exercise tolerance improvements. Physiol Rep, 2018, 6(24), pmcid: 6302546,

[63.] Willmott AGB, Holliss R, Saynor Z, Corbett J, Causer AJ, Maxwell NS. Heat acclimation improves sweat gland function and lowers sweat sodium concentration in an adult with cystic fibrosis. J Cystic Fibrosis, 2021, 20(3): 485-488,

[64.] Willmott AGB, James CA, Hayes M, Maxwell NS, Roberts J, Gibson OR. The reliability of a portable steam sauna pod for the whole-body passive heating of humans. J Thermal Biol, 2023, 118,

[65.] Winter EM, Maughan RJ. Requirements for ethics approvals. J Sports Sci, 2009, 27(10): 985-985,

[66.] World Triathlon. 2022 World Triathlon Championship Finals Abu Dhabi. 2022. https://www.triathlon.org/events/event/2022_world_triathlon_championship_finals_abu_dhabi. Accessed 9 Dec 2023.

Funding

Hong Kong Baptist University