When you exercise, your body quickly warms up. This is mainly because your muscles convert more energy during movement, generating heat. Your body needs to dissipate this heat. You usually notice this first through sweating and increased blood flow to your skin. How warm you get depends not only on the workout. External temperature, your clothing, and the duration of the exertion also play a role. Core body temperature indicates how the temperature inside your body changes during exertion. Understanding these changes can help you better assess how your body reacts to training and how exertion and recovery progress over time.
Why does temperature rise during exercise?
Body temperature rises during exercise because working muscles generate heat. Part of the energy is used for movement. Another part is released as heat. The more intense the exertion, the greater the heat production can be. This effect is barely noticeable during a leisurely walk. During interval training, a long run, or heavy strength training, it is significantly stronger. Warm and humid air can also make heat dissipation more difficult, which can further increase core body temperature during exertion.
How your body regulates heat
Your body has several mechanisms to dissipate excess heat during exercise. These kick in during exertion and adapt to factors such as training intensity and environment:
- Increased skin blood flow: Blood transports heat from the inside of the body to the skin, where it can be released into the environment.
- Sweating: Sweat cools the body primarily when it evaporates from the skin. In high humidity, evaporation may be limited.
- Changes in breathing: During physical exertion, the breathing rate increases. The body can also release heat through exhaled air, although this method contributes less to cooling compared to the skin.
- Adjustment of physical performance: When exertion is reduced or interrupted, muscles generate less additional heat. This allows the body to better adapt heat dissipation to the remaining heat production.
During longer training sessions and in high heat, fluid and electrolyte loss can increase. Therefore, it is important to drink enough and to stop the exertion and seek a cool place if symptoms such as weakness, dizziness, or unusual confusion occur.
What is a normal temperature during exercise?
The question of how high core body temperature can be during exercise cannot be answered with a fixed number. How much core body temperature can rise during exercise depends on factors such as exertion intensity and environmental conditions. A study with eight well-trained male cyclists investigated two different forms of exertion under high heat stress. At a fixed intensity, core body temperature rose faster than at a self-regulated intensity. At the end of the exertion, it was an average of 39.4 °C at fixed intensity and 39.1 °C at self-regulated intensity. The self-regulated exertion lasted slightly longer on average, as participants reduced their performance over time.[1]
Another systematic review evaluated 34 studies on various intermittent sports. In 24 studies, peak core body temperatures between 38.5 and 39.5 °C were observed, and in another six studies, peak values were at least 39.5 °C. Four studies, however, found no evidence of such overheating. The results show that significantly elevated core body temperatures can be observed particularly in intensive intermittent sports under competitive conditions.[2]
When is core body temperature highest?
Core body temperature not only follows training but also a natural daily rhythm. It is usually lower in the early morning than in the late afternoon. This is also shown in a study in which twelve healthy men trained for 30 minutes at moderate intensity at 8 AM and 6 PM. The baseline core body temperature was higher in the late afternoon, averaging 37.15 °C, than in the early morning, at 36.77 °C. At the same time, core body temperature rose less sharply during exertion in the afternoon than in the morning, although the training intensity was comparable.[3]
What influences temperature during a workout?
How much core body temperature rises during training depends on several factors.
These factors make a difference
- Training intensity: Hard intervals and intense strength training generate more heat than light exertion. As intensity increases, so does heat production.
- Training duration: The longer the exertion lasts, the longer the body produces heat. During longer training sessions, more heat can accumulate in the body as a result.
- Air temperature: At high outdoor temperatures, the temperature difference between the skin and the environment becomes smaller. This makes it more difficult for the body to dissipate heat to the environment.
- Humidity: High humidity makes it more difficult for sweat to evaporate, thereby reducing the cooling effect of sweating.
- Clothing: Breathable clothing can aid heat dissipation. Multiple or very dense layers of clothing, however, can trap heat and moisture closer to the body.
- Fluid balance: Severe fluid loss can impair the body's ability to regulate its temperature. Adequate fluid intake is therefore important, especially during longer training sessions and in heat.
The impact of these factors always depends on their interplay. Therefore, core body temperature can develop differently under similar training intensities but varying conditions.
What happens to temperature after training?
Core body temperature does not necessarily return to baseline immediately after training. This is also shown in a study with twelve healthy adults who cycled for 60 minutes and then rested passively for 60 minutes. On average, their mean body temperature had returned to baseline after about 28 minutes. However, core body temperature at this point was still slightly above baseline, averaging 37.5 °C compared to 37.3 °C. The results show that core body temperature can remain elevated even after exertion ends.[4]
How do you recognize excessive heat stress?
An elevated temperature alone does not constitute an emergency. The situation becomes critical if other symptoms occur. These include dizziness, nausea, severe weakness, headache, or confusion. An unusually rapid pulse and severe exhaustion can also indicate problematic heat stress. If you experience heat stress during exercise, you should not try to "train through" the symptoms. Stop the exertion and move to a cool place.
Take warning signs seriously
The body usually gives several clues before a situation becomes dangerous. You should be especially attentive if your condition does not improve despite a break. Pay attention to these signals:
- Severe dizziness
- Nausea and weakness
- Confusion
Heavy sweating in high heat can also lead to significant fluid and electrolyte loss. If the condition worsens, do not wait.
How can you effectively monitor your temperature during exercise?
If you want to understand how your core body temperature changes during exercise, you should first pay attention to what temperature a sensor actually measures. Conventional wearables often measure skin temperature or detect temperature changes using other metrics. For direct measurement of core body temperature, methods such as rectal, esophageal, or gastrointestinal procedures are used in sports science and medicine. However, these methods are only partially practical for everyday use.
This is precisely where the Speediance Strap comes in. The screenless smartband uses greenteg's Calera® technology to continuously measure your core body temperature. The temperature data is combined with other body signals to better assess your physical exertion and recovery. This aims to generate practical recommendations for training and recovery that can help you better adapt your exertion to your individual situation.
For a more comprehensive picture, however, you should not view core body temperature in isolation. Heart rate, training duration, training intensity, ambient temperature, and your personal perception also provide important information about how your body reacts to exertion. Only when these factors are considered together can you better assess how your body copes with a specific training session and the respective external conditions.
Conclusion: Properly assessing core body temperature during exercise
Core body temperature rises during exercise because active muscles generate heat. How much it rises depends on training intensity, duration, environment, and fluid balance, among other things. Understanding how core body temperature changes during and after training can help you better assess your exertion, adapt your training to the given conditions, and more effectively support your performance.
Especially in high temperatures and during longer or intense training sessions, the body's heat stress can increase. Keeping an eye on your body's signals and relevant temperature changes can help you adjust your exertion in time and reduce the risk of heat-related overload. If you experience dizziness, nausea, severe weakness, or confusion, you should stop training immediately and cool down.
Frequently Asked Questions
When is core body temperature highest?
Core temperature is typically highest in the late afternoon or early evening. It is lower in the early morning. Exercise can further increase this value. However, the time of day alone says little about individual resilience.
Why does body temperature rise with exertion?
Active muscles require energy and produce heat in the process. The higher the exertion, the greater the heat production can be. The body increases skin blood flow and begins sweat production, among other things.
How long does temperature remain elevated after exercise?
This depends on the duration and intensity of the exertion. The ambient temperature also influences recovery. After prolonged exertion, the temperature can remain above baseline for some time. Studies describe a return towards baseline within approximately 30 to 120 minutes after prolonged exertion, with individual reactions varying.
Is sweating during exercise a good sign?
Sweating during exercise indicates that the body wants to release heat. However, it does not automatically mean that a workout is particularly effective. In high humidity, sweat evaporates less effectively. Very heavy sweating can also lead to fluid and electrolyte loss.
Sources:
[1] Schlader, Z. J., Raman, A., Morton, R. H., Stannard, S. R., Mündel, T.: Exercise modality modulates body temperature regulation during exercise in uncompensable heat stress. In: European Journal of Applied Physiology, 111(5), 2011, pp. 757–766. Retrieved on September 11, 2026.
[2] Core Body Temperatures in Intermittent Sports: A Systematic Review. In: Sports Medicine, 53(11), 2023, pp. 2147–2170. Retrieved on September 11, 2026.
[3] Aldemir, H., Atkinson, G., Cable, T., Edwards, B., Waterhouse, J., Reilly, T.: A comparison of the immediate effects of moderate exercise in the late morning and late afternoon on core temperature and cutaneous thermoregulatory mechanisms. In: Chronobiology International, 17(2), 2000, pp. 197–207. doi: 10.1081/cbi-100101043. Retrieved on September 11, 2026.
[4] Vargas, N. T., Chapman, C. L., Sackett, J. R., Abdul-Rashed, J., McBryde, M., Johnson, B. D., Gathercole, R., Schlader, Z. J.: Thermal behavior remains engaged following exercise despite autonomic thermoeffector withdrawal. In: Physiology & Behavior, 188, 2018, pp. 94–102. Retrieved on September 11, 2026.
