Heidi said: "I know a lot of people talk about Seal's bicycle shorts, but it is the truth! That is what he was wearing the first time I met him and I was overwhelmed.
"He still wears them now, when he does all of his bicycling stuff or when he runs. He is quite athletic."
The Victoria's Secret model, who made the revelations when she and Seal appeared on Oprah Winfrey's talk show, claims Oprah casts a spell on guests to make them talk freely.
Heidi told People magazine: "I was very happy with how things went on Oprah. It is very strange, you trust her so much that you talk sometimes without realizing what you are saying.
"She has a spell in her eyeballs that when she looks at you, you are like, 'Yes.' "
The couple - who married in May 2005 - have two sons, two-year-old Henry and 11-month-old Johan. Heidi also has a three-year-old daughter, Leni, from a previous relationship with Formula One racing team boss Flavio Briatore.