With two young kids and a limited budget, Charla knew that flashy cars and expensive holidays were out of the question. She needed something unique, something unforgettable. Something that only she could give her husband.

And that's when Charla, a Bible-reading, suburban mom from North Carolina in the US, took a deep breath and decided that she would pledge her husband sex at least once a day for 365 consecutive days.

"I wanted to do something that was very bold and memorable and this fit the bill," she says.

And so, 365 Nights -- a new book written by Charla about the Mullers' year-long sexual adventure -- was conceived (albeit with little details about the actual sex).

"This is not a book about sex," said Charla. "It's a very modest account of being married and trying to figure it all out and trying to stay connected with this person that you've vowed to love and cherish, until death do you part."

If Charla's book is low on sexy, salacious details then Just Do It, another new book about a similar erotic adventure, written by Denver Post journalist, Doug Brown, is guaranteed to make the reader blush.

As a reporter regularly assigned to the sex industry beat, Doug came upon a story about the '100 Days Club' in Denmark, where men who have not had sex in over 100 days "bond over their sad predicament".

The story tickled Doug and he told his wife, Annie, about it as they lay together in bed one night.

"Let's reverse it," said Annie, who as a teenager attended secondary school in Tullamore, County Offaly. "Let's have sex for 100 days."

And so the Browns got down to business. First, they took a long look at their bedroom, made a couple of decorative adjustments and renamed it the 'sex den'.

"We eliminated photographs of old matriarchs and children. We removed children's books and toys from the room. We added candles and incense to the room, and covered the bed with an East Indian bedspread. We also draped a tapestry over the television," said Doug. "We wanted our room to be an adult sanctuary."

Then they turned to themselves. Taking a page out of their early courtship, the couple began to indulge in new nightly rituals.

"Along those lines, we didn't have sex with bad breath," said Doug. "We tried to look good for each other. We treated our nightly engagements as if we were dating again. We would shower. Annie would wear nice lingerie and lipstick. I would not wear my ratty old sweatpants, but instead wear a nice robe or pyjamas."

Committed to making love for 101 days straight -- with no interruptions -- Annie travelled with Doug when he left town on reporting assignments. To spice things up they took weekend trips and bought sex toys and a lot of Viagra (just in case). And with each new venue there was a host of new erotic possibilities.

They did it at 9,000ft on top of a mountain overlooking Colorado. They did it in a nomadic yurt in the woods and in a fancy hotel in Las Vegas, where Doug was covering a porn convention.

They did it in a B&B, in a yoga ashram and on an easy chair. And, with impressive agility, they even did it on an exercise ball.

"We really felt these 101 days were special; we treated it as an adventure," said Doug.

"We didn't spend much money, but we did do more than we would have normally. But we wanted to really treat these 101 days with great respect, and to make them memorable for the rest of our lives".

Both the Mullers and the Browns are at pains to point out that they were extremely happy in their marriages prior to embarking on their 'sexathons'.

But each say that their sex lives had fallen foul of the exhausting regimen of normal married existence. A life with two jobs, two children, a house, long commutes and a mountain of other responsibilities.

"I was one of those spouses who was running around like a chicken with their heads cut off and at the end of the day turning to my husband, and saying, 'Ugh. That too?'" said Charla.

Doug Brown said that he and Annie had sex approximately three times a month prior to their 101-day feast. The Mullers said that their love-making also languished well below the national average of about 66 times a year.

"I knew that that was one thing that I had let fall off the list of important things, so to speak," said Charla, "and I would probably tell you that before the year of 'the gift', you know, maybe a couple of times a month at most."

Indeed, when Charla presented the bemused Brad with 'the gift' she was more than a little crestfallen when the birthday boy politely declined.

"I think he was a little suspicious at such an over-the-top idea," she said. "I think he was worried that perhaps I couldn't follow through or perhaps on one level, he wondered if he could."

But once she had convinced him that her offer was real, Brad joined in enthusiastically. And with busy work and home lives to manage, the couple -- who ended up averaging between 26 and 28 days a month during their experiment -- had to plan their sessions with precision.

"So we would sit down and say, 'I've got book club on Monday night, you've got a sales meeting on Tuesday night. So let's figure out whether morning is going to work for us or maybe right when you get home from work', and things like that," said Charla.

Some experts say that undertaking a sexual marathon for most couples may not resolve the myriad of issues that often lead to a lack of intimacy in marriage.

But the Mullers and Browns are insistent that having sex every night made them happier and closer than they've ever been before and that connecting physically meant that they had to connect first emotionally.

"Nobody needs to do it for 101 consecutive days. But committing to a period of time -- a month, 10 days, a week, a long weekend -- is extremely important for couples that aren't doing it as much as they would like," said Doug.

"Sex is what keeps us from being just pals. It's powerful, it's important and when it declines it harms relationships."

Charla, who now receives emails from women all over America thanking her for her honesty, said the experiment confirmed just how hard it is for a married couple to make their sex life a priority.

"I think I realised what an extraordinarily common experience this is, negotiating intimacy in a committed marriage," she said. "It doesn't matter whether you live in the United States or in Ireland. You're figuring it out."

Both the Mullers and the Browns claim that their sex lives have improved significantly as a result of their adventures and Charla said she and Brad now make love "well above the national average".

Doug said that he and his wife also have upped their frequency and that their experimentation resulted in a number of new positions that they still enjoy. There were also other fringe benefits: "Annie discovered the pleasures of lube and she still marvels over the stuff."

But as the year drew to a close the Mullers' 365 day experiment -- despite its value and meaning -- began to feel like a bit of a chore. By year end, Charla said her gift was becoming her "cross to bear".

"Towards the end of it I thought, 'Holy cow, what have I done? Why did I think this was a good idea?'" she said.

Doug said that although he was "no slouch" during his experiment he too found the going a little rough towards the end. His wife Annie, however, surprised him with her ruthless determination to keep going, even when he ended up in the emergency room with a bout of vertigo.

"Various drugs stopped everything from spinning, but that night after being incredibly sick all day, I did it!" he said. "It was one of the quickest of the quickies but I managed."

They eventually reached their goal of 101 days, and when they did, there was a mixture of triumph and relief.

"We did have sex on the 101st day, and I felt grateful that we had finished. I was ready to rest, though," said Doug.

They didn't have sex for another month.