Last fall, on the heels of the latest studies, the Journal of Sexual Medicine delivered a grim message to male cyclists: Ride enough and you may go permanently limp. Reactions from riders ranged from shock to denial. My bike mechanic's take: "Dude, it's total bullshit!"

If only it were. Many bike seats don't properly meet the "sit bones" under the buttocks; they force the rider to sit directly on the perineum, the zone between the sit bones, squeezing the penile arteries and blocking the flow of blood to the penis. (Well-cushioned seats can be even worse: The comfy softness creeps up between your legs and puts pressure on the arteries there.) Thus begins a disastrous cycle: Loss of oxygen in the penis causes the release of a chemical that triggers the formation of scar tissue, which replaces muscle in the penis. The process is repeated every time you ride until, after years of cycling, you can't get it up.

An avid cyclist myself, I decided to put a number of bike seats -- and my penis -- to the test. I met with an authority on the subject, German surgeon Alexander Kroekel, who wired my member to an oxygen monitor and observed as I rode my bike on a stationary mount. The penis's level of oxygen corresponds to blood flow; the less oxygen, the less blood flowing in, and the greater the chance of impotence.

I first tested the saddle I've had for years, a Trico Sports Memoflex that's dome-shaped and as comfortable as an old sofa. As I pedaled and watched the machine's display, the numbers were clear: In the first minute my seat, a common type, caused a jaw-dropping 85 percent loss in blood flow to my penis.

Next I tried Specialized's Body Geometry Avatar. It was hard and shaped to meet the sit bones, with a cutout where it would hit the perineum. This time my blood flow dropped only 12 percent, not much more than you'd experience sitting in a desk chair.

"If you ride, you're at risk," says Dr. Roger Minkow, an ergonomics consultant for Specialized. But if you ride right, he says, you can minimize that risk.