Why heat hits different for female athletes

When it comes to training or racing in the elements, heat management can separate a strong finish from a struggle to the line or, worse, a DNF. While both male and female athletes face physiological challenges when exercising in hot and humid conditions, the way our bodies respond to heat stress is distinctly different.

For women, understanding these sex-specific differences in thermoregulation isn’t just a matter of comfort; it can support better performance and make the experience more enjoyable, no matter the conditions.

Skewed Understanding

With climate change driving record-setting heatwaves across the globe, training and racing in summer is becoming more complicated for all athletes.

The problem is that general guidelines related to hydration and heat acclimation are often based on studies performed predominantly on men.

Audits and reviews conducted on sports and exercise science research have consistently shown a substantial under-representation of women as study participants.

Female-only studies have historically accounted for a very small percentage of all research in these fields, leading to guidelines primarily underpinned by research conducted on male athletes. 

This is an important realisation because, as with many physiological processes, a woman’s body handles heat much differently to a man’s, which means they often need a different approach.

The Science of Staying Cool

Thermoregulation is your body’s ability to maintain a stable core temperature despite changing external conditions.

During exercise, your heart rate rises to supply oxygen to your working muscles, skin (for cooling), and vital organs.

When exercising outdoors in hot and humid conditions, muscle contractions generate heat. To prevent overheating, the body increases blood flow to the skin and activates sweat glands to help cool through evaporation.

In the heat, your body prioritises those demands by decreasing blood flow to your gut and liver, which can spell trouble for both men and women as there are fewer resources to support digestion and nutrient absorption, especially as temperatures creep past 24°C. 

However, that’s where the similarities between our thermoregulatory responses typically end.

Sex-specific Differences

Due to sex-specific differences in thermoregulation, female athletes might find that they get more fatigued or experience more severe gut issues than their male counterparts in the same conditions, even though their hydration and fuelling strategies tick all the recommended boxes.

For starters, women generally produce less sweat than men at the same relative intensity. That doesn’t mean they’re less efficient at cooling, though. It means they rely more on blood flow redistribution and heat dissipation through the skin, rather than purely on sweat evaporation.

A study¹ conducted by Japanese researchers affirmed this difference. Findings showed that while physical training increases sweat rates in both men and women, the degree of increase is greater in men.

This difference relates to a higher sweat output per gland in men compared to women, even when matched for aerobic capacity or training status. Furthermore, men sweated more as exercise intensity increased.

Studies² also indicate that women exhibit a greater overall exercise vasodilation response in active muscles compared to men, which is crucial for maintaining a stable core body temperature during physical activity, which generates considerable metabolic heat.

Hormones and Heat

Hormones play a significant role in how women regulate temperature. Oestrogen and progesterone, which fluctuate across the menstrual cycle, influence both core temperature and sweat response³.

• Oestrogen: Peaks just before ovulation in the follicular phase, tends to promote heat loss by improving blood flow to the skin.
• Progesterone: Slightly raises resting core temperature and delays the onset of sweating.

This phenomenon means that in the luteal phase – the second half of the cycle (about 5 to 7 days after ovulation), when progesterone is higher – women may feel warmer, sweat later, and find it harder to offload heat during hard efforts, especially in warm weather or high humidity. It’s subtle but noticeable in endurance scenarios, where small inefficiencies accumulate over hours.

Previous studies⁴ have also shown that men have a higher sweat output than women, in part because testosterone is believed to enhance the sweat response.

Sex hormones also control fluid balance, water and sodium in the body⁵, as progesterone competes with aldosterone, a hormone that retains sodium.

The outcome, especially in the high-hormone phase of the menstrual cycle or oral contraceptive use, is a greater amount of water retention, contributing to lower sodium levels, which can increase the risk of Exercise-Associated Hyponatremia (EAH).

Body Composition and Heat

Differences in body composition are another key factor in these sex-specific differences in how men and women heat up and cool down.

A woman’s typically smaller body size and lower relative muscle mass, compared to men, significantly influence her ability to regulate body temperature. 

The lower relative muscle mass in women directly impacts heat production by lowering a woman’s Basal Metabolic Rate (BMR), because muscle tissue is more metabolically active than fat, producing more heat even at rest. As such, a woman’s lower muscle mass means she produces less total metabolic heat during a fixed workload exercise than a man.

Women also typically have a higher body fat percentage relative to men. Fat acts as insulation, which is helpful in the cold, but counterproductive in the heat.

The result is that women may heat up more slowly, but also tend to cool down less efficiently once overheated, particularly when environmental conditions reduce the effectiveness of sweating.

Additionally, a woman’s smaller body size and higher surface area-to-mass ratio can sometimes offer an advantage in milder heat, allowing for faster heat exchange. However, as temperatures rise and humidity spikes, this benefit diminishes.

Hydration and Electrolytes

Because women tend to sweat less, they typically lose smaller absolute volumes of fluid and sodium, but that doesn’t mean hydration is less important to female athletes.

As men and women differ in their hydration needs at rest and during prolonged exercise, an individualised strategy is vital.

An important consideration is hydration status at the start of a race, as women tend to have lower total body water levels.

Coupled with lower sweat gland output, losing the same percentage of body mass through sweat may represent a larger proportion of total body water loss in women.

While drinking more may seem like an appropriate approach, over-drinking can be just as risky because hyponatraemia (low blood sodium) is more common among smaller, lighter athletes who consume large amounts of water without adequate electrolytes.

Some studies show that female athletes have a higher incidence of EAH, typically due to their lower body weight and smaller fluid compartments compared to men, as well as a potential tendency to overhydrate based on general hydration advice.

As such, women need a measured hydration plan that uses thirst cues and body weight changes between the start and end of sessions and races as guidelines, rather than relying on rigid fluid intake schedules.

However, drinking plain water won’t cut it. It absorbs slowly and can pull sodium and water into your gut, which hinders, rather than helps, hydration and energy levels. And relying solely on electrolyte-infused drinks isn’t the answer either.

Women should also include a mix of high-carb drinks for energy, and hypotonic energy drinks formulated with glucose and sucrose to enhance fluid absorption from the gut into the body and keep osmolality below that of blood.

Too many hypertonic drinks, like high-carb mixes, can slow down fluid absorption and often cause bloating, cramping, or diarrhoea.

The right approach is a strategy that includes the right balance of electrolytes and hypotonic and hypertonic energy drinks to ensure your gut absorbs fluid efficiently and maintains blood volume without compromising on your carb intake.

An additional research-backed recommendation⁶ is to supplement with L-glutamine for seven days before any race that will take place in hot conditions. This supplement strategy may help gut function and reduce the effects of heat.

Acclimation and Adaptation

Interestingly, while men generally sweat more, women’s thermoregulatory systems tend to adapt faster to heat training⁷.

If you know you’ll be racing in hot and humid conditions, repeated exposure through a structured heat-acclimation block – typically 10-14 days – or training during warm times of day can improve sweat response and cardiovascular efficiency.

This suggests that women who train smartly in the heat can close much of the performance gap, especially if they tailor recovery, hydration, and intensity around their cycle.

Ultimately, women aren’t less capable in the heat; female bodies just respond differently. Understanding those physiological nuances allows female endurance athletes to plan smarter, race stronger, and recover faster.

References:

1. Ichinose-Kuwahara, T., Inoue, Y., Iseki, Y., Hara, S., Ogura, Y., & Kondo, N. (2010). Sex differences in the effects of physical training on sweat gland responses during a graded exercise. Experimental Physiology, 96(3), 263–272. https://doi.org/10.1113/expphysiol.2010.053710.
2. Kellawan JM, Johansson RE, Harrell JW, Sebranek JJ, Walker BJ, Eldridge MW, Schrage WG. Exercise vasodilation is greater in women: contributions of nitric oxide synthase and cyclooxygenase. Eur J Appl Physiol. 2015 Aug;115(8):1735-46. doi: 10.1007/s00421-015-3160-6. Epub 2015 Mar 28. PMID: 25820143; PMCID: PMC4506238.
3. Greenfield AM, Charkoudian N, Alba BK. Influences of ovarian hormones on physiological responses to cold in women. Temperature (Austin). 2021 Sep 14;9(1):23-45. doi: 10.1080/23328940.2021.1953688. PMID: 35655670; PMCID: PMC9154773.
4. Inoue Y, Ichinose-Kuwahara T, Funaki C, Ueda H, Tochihara Y, Kondo N. Sex differences in acetylcholine-induced sweating responses due to physical training. J Physiol Anthropol. 2014 May 29;33(1):13. doi: 10.1186/1880-6805-33-13. PMID: 24887294; PMCID: PMC4050411.
5. Rowlands, D. S., Bonetti, D. L., & Hopkins, W. G. (2011). Unilateral Fluid Absorption and Effects on Peak Power After Ingestion of Commercially Available Hypotonic, Isotonic, and Hypertonic Sports Drinks. International Journal of Sport Nutrition and Exercise Metabolism, 21(6), 480-491. Retrieved Nov 4, 2025, from https://doi.org/10.1123/ijsnem.21.6.480.
6. Pugh, J.N., Sage, S., Hutson, M. et al.Glutamine supplementation reduces markers of intestinal permeability during running in the heat in a dose-dependent manner. Eur J Appl Physiol 117, 2569–2577 (2017). https://doi.org/10.1007/s00421-017-3744-4.
7. Kobayashi Y, Ando Y, Okuda N, Takaba S, Ohara K. Effects of endurance training on thermoregulation in females. Med Sci Sports Exerc. 1980;12(5):361-4. PMID: 7453515.