Performance Benefits of Heat Acclimation for Athletes

Written By Alyson Freitag

Summers in Missoula continue to get warmer & for many that means setting the alarm earlier for their workouts. However, research shows that heat training can be very beneficial in preparation for races & overall exercise performance. Perhaps hitting snooze & moving your exercise plans to a warmer time of day isn’t such a bad idea! Learn more about what heat training is, its benefits, & how to get started below. 


What Is Heat Acclimation Training?


Heat acclimation is “a biological adaptation that reduces physiological strain (e.g. heart rate & body temperature), improves comfort, improves exercise capacities & reduces the risk of serious heat illness during exposure to heat stress” (1). Acclimation training involves a gradual increase in repeated heat exposure to induce thermoregulatory adaptation to improve exercise function & efficiency in warm conditions. The combination of heat stress & physical activity interact synergistically to increase the strain on physiological systems (2). 


There are three classic signs that heat acclimation has been achieved: lower heart rate, lower core temperature, and a higher sweat rate during exercise heat stress (1). For many athletes these are fairly easy signs to monitor during training. Once heat acclimation has been achieved you can expect your skin temperature to be lower & to begin sweating earlier in your workout with a greater sweat volume throughout. The increase in sweat excretion demonstrates your body’s efficiency with evaporative cooling. Lower skin temperature requires less demand for blood flow to maintain heat balance & allows a more efficient blood volume distribution to the central circulation redistributed from the peripheral circulation, reducing cardiovascular strain & improving exercise-heat performance (4). 

Kilian Journet at The RUT

Performance Benefits from Heat Acclimation Training:

  • Fluid balance improvements: 

    • Acclimated athlete’s sweat glands conserve sodium by secreting sweat with sodium concentrate as low as 10 mmolL-1, compared to unacclimated at around 60 mmolL-1 (1). Thus, an acclimated athlete would have less sodium replenishment during long duration activity. 

  • Acquired thermal tolerance

    • Molecular adaptations provide protection & expedite repair from heat stress, ischemia, monocyte toxicity, & UV radiation (3)

  • 23% improvement in time-to exhaustion (3)

  • Studies show overall improvements in: heart rate, core temperature, skin temperature, power output at lactate threshold, increase in plasma volume, greater max cardiac output (1, 2, 3)   

Ways to Achieve Heat Acclimation: 

  • 3 main approaches: constant metabolic rate, self-paced training, controlled hyperthermia

    • Sustained HR during exercise heat exposure optimizes greatest adaptations (3) 

  • Research says that 90 minutes of aerobic exercise in the heat shows the greatest benefits, although being in a heat environment for 90 minutes does have some benefit as well 

  • While there is some variation in training techniques, overall studies agree that gradual increases in exercise intensity & duration in the heat is the best way to induce adaptations. It is best to replicate exercise duration & intensity of your sport during training.

  • 7-14 days of exposure are needed to induce heat acclimation. Physiological strain will be greatest on day 1 of heat training & decrease subsequently as acclimation continues. The greatest responses in heart rate, skin & core temperature, & sweat rate are seen in first 7 days & plateau by day 10-14 (1).

  • Passive modalities including hot water immersion (30 minutes at 40* C) or sauna (10-15 min, 90* C) can help to prolong benefits directly following activity

  • Acclimating in a cooler environment?

    • Layer up to stimulate a warmer environment

    • Perform cardio training first to sustain greater HR & sweat production throughout workout

    • Utilize passive modalities (ie: sauna, hot tub, steam room)

  • In order to maintain heat acclimation adaptations: intersperse a heat training day every 3rd training day 

Precautions:

  • Monitor sweat loss to avoid dehydration

    • Total sweat loss= (pre-exercise BM - post-exercise BM) + fluid intake

      • >2% body water (.6* BW) loss leads to decreased performance

  • Inadequate nutrition

    • Muscle glycogen depletion is accelerated in heat. Recommended to intake 30-60 g of carbohydrates for each hour of activity 

    • Consider sodium intake during exercise

    • Water intake. Take a sip of water every 10-15 minutes of exercise, drink water before you feel thirsty

  • Warning signs of heat exhaustion: dizziness, thirst, heavy sweating, nausea, weakness

  • Warning signs of heat stroke: confusion, dizziness, loss of consciousness




Is Training in Heat > Altitude Training?

  • Greater changes in physiological strain index found following heat training compared to hypoxic environment

  • Heat acclimation improved time trial performance to a magnitude similar to that achieved by hypoxic acclimation (altitude training). It also improved cellular & systemic physiological tolerance to exercise at altitude (5).

  • Pros & cons to both

    • Altitude: 

      • Pros: increase RBC count, capillary density, improved oxygenation to the muscles

      • Cons: decreased ability to recover, speed of training typically slows at higher altitude

    • Heat

      • Pros: decreased HR, increased blood plasma volume, increased max cardiac output, decreased core temperature, body adapts quicker than to altitude training, & more accessible than altitude training

      • Cons: greatest effects occur in outdoor heat training & is not accessible year round

Written by: Adison Cook, SPT


References: 

(1) Heat acclimatization to improve athletic performance in warm-hot environments. (n.d.). Retrieved August 10, 2022, from https://www.gssiweb.org/sports-science-exchange/article/sse-153-heat-acclimatization-to-improve-athletic-performance-in-warm-hot-environments

(2) Lorenzo, S., Halliwill, J. R., Sawka, M. N., & Minson, C. T. (2010). Heat acclimation improves exercise performance. Journal of Applied Physiology, 109(4), 1140-1147.

(3) Pryor, J. (n.d.). Application of evidence-based recommendations for heat acclimation: Individual and team sport perspectives. Retrieved August 10, 2022, from https://www.tandfonline.com/doi/full/10.1080/23328940.2018.1516537?scroll=top&needAccess=true

(4) Sawka, M. N., Leon, L. R., Montain, S. J., Sonna, L. A., & Army Research Inst Of Environmental Medicine Natick Ma Thermal And Mountain Medicine Division. (2011, October). Integrated physiological mechanisms of exercise performance, adaptation, and Maladaptation to heat stress. DTIC. Retrieved August 19, 2022, from https://apps.dtic.mil/sti/citations/ADA559128 

(5) Lee, B. J., Miller, A., James, R. S., & Thake, C. D. (1AD, January 1). Cross acclimation between heat and hypoxia: Heat acclimation improves cellular tolerance and exercise performance in acute normobaric hypoxia. Frontiers. Retrieved August 19, 2022, from https://www.frontiersin.org/articles/10.3389/fphys.2016.00078/full 






Alyson Freitag
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