Female Thermoregulation: Why Individualized Thermal Data Is So Important

As Meg Smith, Doctoral Researcher and Performance Physiologist at Loughborough University and Performance Physiologist at AG Insurance-Soudal Team, explains: "At AG Insurance-Soudal, we recognise that every rider is different. Menstrual cycle tracking provides valuable context, but it is only one piece of the puzzle and is most meaningful when considered alongside other physiological, performance and wellbeing measures used to support athlete health and performance."   

A similar approach is used at FDJ-SUEZ. Lieselot Decroix, PhD, Performance Manager at FDJ-SUEZ, notes: "Cycle tracking is both an important health marker to follow, but also equally important in following and analyzing performance, training load and subjective feelings."  

Together, menstrual cycle information and CORE thermal data can provide valuable context for understanding why two athletes may respond very differently to the same training session or race conditions.  

Both men and women maintain a core body temperature around 37°C, but hormonal fluctuations mean thermoregulation is often more variable in women.  

Estrogen and progesterone directly influence the hypothalamus, the brain's temperature control center. As progesterone rises during the luteal phase, resting core temperature increases and the threshold for activating cooling responses such as sweating shifts upward.  

Research has shown that women generally rely more on increased skin blood flow and less on sweat production than men during heat exposure. Combined with menstrual cycle-related hormonal changes, this can alter heat tolerance, thermal strain, and recovery demands throughout the month.  

As a result, a female athlete may effectively become a different "thermal athlete" at different points in her cycle.  

The menstrual cycle is commonly divided into two primary phases:  

• Follicular phase: From menstruation through ovulation  
• Luteal phase: From ovulation until the next menstrual cycle  

As progesterone rises during the luteal phase, resting core temperature typically increases by ~0.3-0.5°C and the threshold for activating cooling responses such as sweating shifts upward. Research suggests that thermal strain is generally greater during the luteal phase, even when performance differences across the cycle are relatively small.   

For athletes training or racing in the heat, this can influence:  

• Perceived exertion  
• Hydration requirements  
• Cardiovascular strain  
• Recovery demands  
• Heat tolerance during key sessions  

However, the practical impact differs substantially between athletes. As Decroix explains: "How riders react, not only to heat, during different phases of their cycle is very individual. Some riders subjectively report having a harder time dealing with the heat in the luteal phase, while others don't feel anything."  

This variability highlights why individualized monitoring is often more useful than relying solely on population averages.  

Research suggests that, on average, women tend to produce less sweat per gland and rely more on increased skin blood flow to dissipate heat, whereas men generally rely more heavily on evaporative cooling through sweating.  

Women also experience greater variability in thermoregulatory responses across the menstrual cycle. Changes in estrogen and progesterone can alter resting core temperature, sweating thresholds, perceived heat stress, and recovery demands.  

As a result, two athletes completing the same workout under identical environmental conditions may experience very different levels of thermal strain, even when pace, power, and heart rate appear similar.  

This variability is exactly why monitoring core temperature can be valuable.  

Traditional training metrics such as pace, power, and heart rate only tell part of the story. Core temperature provides additional insight into how the body is responding to heat stress, making it particularly valuable for female athletes, whose thermal responses can shift throughout the menstrual cycle.  

As Meg Smith explains: "By tracking the menstrual cycle, we can start to understand how it links to other aspects of performance. Without that tracking, things can appear much more random and it's harder to connect the dots."  

At the same time, monitoring should come before conclusions. As Lieselot Decroix notes: "It remains our priority to monitor these changes before drawing conclusions."  

Combining menstrual cycle tracking with thermal monitoring may help identify:  

• Higher thermal strain during the luteal phase  
• Changes in heat tolerance during racing or travel  
• Differences in hydration and recovery needs  
• Early signs of accumulated fatigue  

Thermal data is also increasingly being used to inform practical performance decisions. As Decroix explains: "In defining pace plans for time trials or long climbing efforts in 35-40°C conditions, we consider the heat load that we would expect to build up during the effort using data from previous weeks."  

Rather than relying solely on external workload metrics, coaches can use thermal data to better understand each athlete's physiological response and individualize training, cooling, recovery, and race strategies.  

Heat adaptation remains one of the most effective tools for improving endurance performance and resilience in challenging conditions.  

Decroix emphasizes that heat acclimation can be particularly valuable for female athletes: "We certainly saw some riders struggle more with the heat than others. It was a good sign for some riders to invest more in heat training, as for females it might be even more important to take the time to adapt to the heat compared to males."  

Female athletes can absolutely benefit from heat training. The key is understanding that heat adaptation may not feel identical throughout the cycle.  

According to Meg Smith, sometimes, the most noticeable effects often occur away from the training session itself: "What we tend to notice isn't always during the heat session itself. Sometimes, it’s afterwards. Some riders report feeling hotter throughout the day and experiencing more disrupted sleep after heat training during the luteal phase."  

During the luteal phase, athletes may notice:  

• Higher starting core temperatures  
• Faster cardiovascular drift  
• Earlier perception of fatigue  
• Greater difficulty dissipating heat  

This does not mean heat training should be avoided. Instead, the goal is to individualize the approach. As Smith explains: "For some riders, we'll replace active heat sessions with passive heat exposure in the week before their period. The goal is to maintain heat exposure without adding unnecessary physiological and thermal stress." Some teams may also shift training earlier in the day to allow more time for thermal load to dissipate before sleep. " For some riders, we may shift training earlier in the day during the luteal phase. The aim is to support recovery and sleep by giving the body more time to dissipate heat before bedtime, although responses vary considerably between individuals."  

Importantly, menstrual cycle phase is rarely considered in isolation. As Decroix notes: "We haven't modified heat-training sessions just based on menstrual cycle, as we have many factors to consider, including race planning, training periodization, subjective feelings, recovery and sleep."  

This reflects the reality of elite sport, where menstrual cycle information is combined with thermal data, training load, recovery metrics, and athlete feedback to guide individualized heat-training and race-preparation strategies.  

Hormonal contraception can influence thermoregulation by altering hormone levels throughout the month. Depending on the contraceptive type, this may result in a chronically elevated resting core temperature similar to that observed during the luteal phase.  

However, responses vary considerably between athletes, highlighting the importance of individualized monitoring. As Smith notes: " In our experience, riders who use hormonal contraception often show more stable RHR and HRV metrics overtime. However, there is considerable variation between individuals, which reinforces the importance of interpreting these metrics within the context of each rider."  

While the physiological effects depend on contraceptive type and individual responses, this observation suggests that hormonal status may influence both thermoregulation and recovery during heat adaptation.  

Low energy availability can also disrupt thermoregulation. Conditions such as Relative Energy Deficiency in Sport (REDs) and Functional Hypothalamic Amenorrhea (FHA) alter reproductive hormone function and can impair multiple physiological systems involved in heat regulation.  

Athletes experiencing REDs may experience:  

• Altered sweating responses  
• Impaired recovery  
• Increased physiological strain during exercise  
• Reduced tolerance to repeated heat stress  

Although research on heat adaptation in athletes with low energy availability remains limited, observations from elite cycling teams suggest that menstrual status may influence recovery from heat training.   

Smith explains: "One observation we’ve made is that the riders that don't have a cycle tend to show a more progressive drop in HRV throughout a heat block, whereas riders with a cycle generally show a better day-to-day rebound." Based on these observations, AG Insurance-Soudal has adjusted some heat-acclimation strategies, with athletes experiencing amenorrhea often completing larger heat blocks further from key competitions and maintaining adaptations with shorter top-up sessions.  

While these observations should not be interpreted as evidence of cause and effect, they reinforce the importance of considering menstrual status, hormonal health, and energy availability when planning heat-training interventions.  

Female athletes are not simply smaller versions of male athletes. Their physiological responses to heat are more variable and more influenced by hormonal changes throughout the month. That variability is not a limitation. It is a reality of human physiology that deserves better measurement and better understanding.  

As Smith emphasizes: " It's very easy to overstate the influence of the menstrual cycle. At AG, we don't view it as an explanation for everything. Rather, we view it as one piece of a much bigger performance puzzle."  

As elite sport continues moving toward individualized performance strategies, thermal data provides an opportunity to better understand how female athletes respond to training, racing, heat, travel, and recovery in real-world environments.  

The goal is not to make assumptions based on menstrual cycle phase alone, but to understand each athlete's unique physiological response. The future of heat training is not built around generalized averages. It is built around individualized physiology.  

Expert Contributors  

Meg Smith  Doctoral Researcher and Performance Physiologist, Loughborough University; Performance Physiologist, AG Insurance-Soudal Team  

Lieselot Decroix, PhD  Performance Manager, FDJ-SUEZ