Influence of moderate cycling on scrotal temperature.

Plain-language summary

It has been suggested that cycling warms the testicles as a ride goes on, and that this in turn harms semen quality. This study tested the first half of that and not the second: it measured scrotal temperature and took no semen sample at all. Twenty-five volunteers with no history of infertility and a normal examination cycled for 60 minutes on an exercise bike at 25 watts, which is a light load, in a room held at 22 degrees Celsius (72 degrees Fahrenheit), in standardized cotton clothing, with temperature sensors on both sides of the scrotum and one on the saddle. Scrotal temperature barely moved and did not climb as the hour went on. It was in fact significantly lower while they were riding than it had been while they sat still beforehand.

Key findings

• Scrotal temperature moved from 35.75 to 35.82 degrees Celsius (96.35 to 96.48 degrees Fahrenheit) on the left side over the hour, and from 35.50 to 35.59 degrees Celsius (95.90 to 96.06 degrees Fahrenheit) on the right.
• Scrotal temperature while riding was significantly lower than while sitting still beforehand, by 1.31 degrees Celsius (2.36 degrees Fahrenheit) on the left and 1.46 degrees Celsius (2.63 degrees Fahrenheit) on the right.
• Scrotal temperature did not climb as the hour went on. Every man rode the same 60 minutes, so the study says nothing about rides of other lengths.
• The saddle surface reached 35.59 degrees Celsius (96.06 degrees Fahrenheit) after the hour.
• No semen sample was taken, so this study reports nothing about semen quality either way.
• The authors conclude that moderate cycling at 25 watts is not a major source of genital heat stress.