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I've heard that riding a bicycle, especially for extended periods of time reduces sperm count/fertility. HERE's an example of such a discussion in a bike forum going back and forth about whether it's true or not.

I realize that two of the questions above discuss the link between either tight fitting clothes and temperature increase, but I'm unsure about whether such conditions apply when bicycling or not.

Questions

  • Is this just folklore, or are the conditions created when riding a bicycle sufficient that one might actually experience a reduction in fertility?
  • If the previous answer is "Yes," is the effect severe, and what is the duration of the effect (in other words, is it even worth worrying about)?
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About as much as is causes cancer. –  Alain Jun 24 '11 at 18:58
    
Some bicycle seats are cushion-padded and more comfortable for longer rides; would these at least be safer for want-to-be fathers? –  Randolf Richardson Jun 25 '11 at 7:12
    
@Randolf: I'd heard that the skinny seats were actually better for longer rides, but don't recall why. I think they target having your weight rest on your two "butt bones" instead of cushioning everything. The problem with the cushy seats is friction over time as your legs rub past that big seat. –  Hendy Jun 25 '11 at 13:44
    
Wider seats also cause chafing in your thighs for longer rides, another reason many (but far from all) cyclists avoid them. –  neilfein Jun 27 '11 at 15:35
2  
I ride a lot and lose feeling in my groin area on longer ride. If you sit incorrectly, you can numb the area by closing off the blood supply. –  Hairy Jun 28 '11 at 10:58

2 Answers 2

This pubmed abstract: http://www.ncbi.nlm.nih.gov/pubmed/20102446 seems to indicate that there is a relationship between bicycle riding and erectile dysfunction through perineal compression. This abstract is from a literature review and indicates more research is needed.

This study indicates that all seats lead to a decrease in penile oxygen pressure: http://www.ncbi.nlm.nih.gov/pubmed/12074400 but that the wider the seat the better.

None of the studies talked about sperm count. Their main concern seemed to be erectile dysfunction through decreased blood flow, oxygen availability and perineal compression.

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It seems legit.

LiveStrong and the BBC both reference a 2009 Cordoba study.

I believe those are talking about "Sperm morphology normalcy is inversely correlated to cycling kilometers in elite triathletes" which concludes:

The main finding of the present study is that cycling training volume inversely correlates to sperm morphology. That is, athletes with the highest weekly training volume (greatest distance covered in km) had the lowest percentage of normal sperm.

You have to cycle more than 100km a week for there to be a measurable effect.

De Souza and colleagues established that, in order to observe alterations in semen parameters, a minimum effective volume of a 100 km/week had to be attained

...

Moreover, it seems that those systematically covering distances over 300 km per week would have values so low that they would be included in the p-group (poor prognosis) with regards to pregnancy outcome according to Kruger's newest categorization.

Quite a few regular riders will do 100km over a sunny weekend but few do 300km/wk unless they also commute by bike during the week.

The cause does seem to be compression and heating and possibly damage to the testes.

This condition may be further aggravated in cycling where subjects are clearly exposed to mechanical compression and irritation, even sometimes producing a microtrauma, of the testes, epididymis, and vas deferens during cycling27,28. Due to such compression, a reduction in blood flow may occur; this aspect is of special importance since nutrition of the sperm cell line-ages may be impaired.

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