LET’S say you and your spouse haven’t had sex in so long that you can’t remember the last time you did. Not the day. Not the month. Maybe not even the season. Would you look for gratification elsewhere? Would you file for divorce? Or would you turn to your mate and say, “Honey, you know, I’ve been thinking. Why don’t we do it for the next 365 days in a row?”

That’s more or less what happened to Charla and Brad Muller. And in another example of an erotic adventure supplanting married ennui, a second couple, Annie and Douglas Brown, embarked on a similar, if abbreviated journey: 101 straight days of post-nuptial sex.

Both couples document their exploits in books published this month, the latest entries in what is almost a mini-genre of books offering advice about the “sex-starved marriage.” The couples, though, are hardly similar. The Mullers are Bible-studying steak-eating Republicans from Charlotte, N.C. The Browns are backpacking multigrain northerners who moved to Boulder, Colo. The Mullers’ book, “365 Nights,” is rather modest and circumspect in its details. The Browns’ book, “Just Do It,” almost makes the reader feel part of a threesome, sharing everything they used to stimulate sexual desire (it’s hard to visualize and even harder to explain).

To many spouses, “married sex” may sound like an oxymoron. And “married-with-children sex” may sound like that elusive antimatter. Indeed, reigniting a couple’s desire for each other has fueled an entire therapeutic industry  from Kinsey to Dr. Ruth to Redbook. According to a 2004 study, “American Sexual Behavior,” by the National Opinion Research Center at the University of Chicago, married couples have intercourse about 66 times a year. But that number is skewed by young marrieds, as young as 18, who couple, on average, 109 times a year.