Pick up the nearest book of 123 pages or more.
Ha ha. It is Yoga: The Path to Holistic Health - the anniversary edition that celebrates Iyengar's 90th birthday. Yes, I have it just lying around at my desk.
Find Page 123.
Find the first 5 sentences.
They list the benefits of Paschimottanasana, among which is the treatment for impotence. I kid you not.
Post the next 3 sentences.
THE GURU'S ADVICE
"Stretch from the seat of the buttocks and feel the lightness in your buttock. This is the heart of the perfect pose."