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Scrotal temperature change during running in naked humans
Yasuho Takii1, Makoto Fukuda2, Kazuyuki Kanosue3,4
1Institute of Sport Science, ASICS Corporation, Kobe, 651-2271, Hyogo, Japan. yasuho.takii@asics.com.
Scientific Reports
|October 30, 2025
Summary
Running temporarily increases scrotal temperature in male runners, despite overall body cooling. This suggests rapid thermoregulation adjustments in the scrotum, possibly involving muscle contractions and blood flow changes.
Area of Science:
- Physiology
- Exercise Science
- Reproductive Biology
Background:
- High body temperature negatively impacts male reproductive organ function.
- Understanding scrotal thermoregulation is crucial for male reproductive health, especially during physical activity.
Purpose of the Study:
- To investigate the thermoregulation mechanisms of the human scrotum during running.
- To analyze temperature changes in the whole body and scrotum during exercise.
Main Methods:
- Eleven male long-distance runners participated in treadmill running at 60% VO2max for 60 minutes.
- Environmental conditions were controlled at 27°C and 40% relative humidity.
- Skin temperatures of various body parts, including the scrotum, were monitored.
Main Results:
- Scrotal temperature increased immediately upon starting the run, while other skin temperatures decreased.
- Post-run, scrotal temperature decreased, and other skin temperatures increased.
- The initial scrotal temperature rise occurred independently of thigh contact, suggesting active physiological responses.
Conclusions:
- Running induces a rapid, initial increase in scrotal temperature, distinct from general body cooling.
- This phenomenon may be mediated by dartos and cremaster muscle contraction due to sympathetic nervous system activity.
- Specific vasodilation mechanisms might also contribute to scrotal temperature regulation during exercise.
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