It's all so intense in the beginning of a relationship.

Sex is priority number one—who cares about sleep? Or work? Or really anything that doesn't involve getting naked? But over time, the urgency to tear off each other's clothes gives way to more mundane activities, such as eating breakfast and showering. Nobody plans for the heat to dissipate. It just does.

The first signs of a slump from your once super sex often appear around the two-year mark, when you've settled into a comfortable long-term romance. "As your relationship gets better and more secure, the sexual excitement may fade," cautions couples and sex therapist Jane Greer, Ph.D., author of What About Me? "Since you know he's not going anywhere, there's little motivation to pull out all the stops in bed to impress him like you did when you first started dating, and vice versa. So sex starts to become routine."

To make matters worse, the hormones that are responsible for boosting your bedroom bliss pull a disappearing act right when you need them most. "In the beginning of a relationship, the sex hormones estrogen and testosterone, dopamine (the pleasure neurotransmitter), and oxytocin (the bonding hormone) spike," says Barbara Bartlik, M.D., a sex therapist in New York. "But they can decline back to base levels at about 24 months."

Scientists aren't exactly sure why things fizzle, but they suspect it has something to do with evolution. "In the human species, newborns have the best chance of survival when they have two parents during their first couple of years of life," says biological anthropologist Helen Fisher, Ph.D., author of Why Him? Why Her? "So whether or not you decide to have kids, you're hardwired to form a strong two-year sexual bond, which acts as superglue to ensure neither parent leaves for another mate while the child is still developing."

That's not to say you can't tinker with that wiring. In fact, simply switching up the types of sex you have can completely reinvigorate your relationship in ways you've never imagined. "Mixing up erotic styles keeps your sex life in shape, just like mixing up your workouts keeps your body fit and challenged," says Miro Guldelsky, D.H.S., a sex therapist in New York City. Not only that, but "continuing to play around with novel types of sex allows you to uncover your sexual preferences—ones you may not have even known you had," says Greer. "And as a couple evolves, adding different dimensions to their sex life will strengthen the relationship overall."

Behold the four types of sex that experts say you should add to your repertoire.

Maintenance Sex

"Think of this as meat-and-potatoes sex—it happens at the end of the day, during the week, when a run-of-the-mill romp is all you have energy for," says Pepper Schwartz, Ph.D., a professor of sociology at the University of Washington and author of Prime: Adventures and Advice on Sex, Love, and the Sensual Years.

Having sex while Jay Leno blares in the background doesn't sound particularly erotic (nothing against you, Jay), but it's a necessary part of every couple's sex life. "This is the kind of sex that connects you and reaffirms your bond as a couple," says Gina Ogden, Ph.D., a researcher and sex therapist in Cambridge, Massachusetts, and author of The Return of Desire.

On the nights you're too drained for long, drawn-out foreplay, boil it down to a couple of well-placed caresses that you can count on to expedite arousal. When you're both riled up enough for intercourse, the goal is to orgasm—fast. To that end, choose O-friendly positions that lend themselves to clitoral contact. Woman on top is your best bet because it lets you control the pace, but don't count out positions that allow for manual stimulation (side by side, from behind).

You probably won't break the bed or wake the neighbors with this kind of sex, but you'll fall asleep satisfied, which is all that matters. "You don't want this to be the only way you have sex, but you should have it a lot," says Schwartz. "So if you're having sex four times a week, maintenance sex should account for two or three of those times."



Spontaneous Sex

When you're in a new relationship, every surface becomes a potential place to get horizontal. The result? Primal, breathless, passionate sex. Too bad it's the first type to go when hormone levels start to dip. Without those frisky chemicals buzzing around—urging you to jump him anytime, anywhere—sex moves to your brain's back burner. To recapture the animal attraction that leads to spontaneous sex, you need to act like you did when you first got together and were having sex all the time. In other words, keep up with the bikini waxes, wear your pretty underwear (or no underwear at all—your call), get a spray tan, hit the gym. Basically, do whatever it is that makes you feel confident and sexy. "Feeling attractive and desired by your partner promotes arousal," says sex therapist Sandor Gardos, Ph.D., founder of MyPleasure.com. "It helps prime you for sex."

Seize opportunities when they present themselves and whenever you feel inspired. Join him in the shower before work. Pull over on the side of the road on the way home from a party. Put your hand in his lap while you're sitting on the couch watching TV together. The beauty of sex is that once you put in a little effort, it quickly starts to pay off: An Emory University study found that your body can become aroused physically before you start mentally desiring sex.

Unlike maintenance sex, spontaneous sex doesn't need to happen all the time. "Your sex life isn't a movie," says Schwartz. "Aim for once a week or so."

Rediscovery Sex

Having a big argument (he blew your vacation fund during a friendly game of poker), hitting a major life milestone together (it's a girl!), or weathering a rocky period in your relationship (someone cheated) aren't the kind of events that you'd expect to put you in the mood, but they can inspire sex that's intense, urgent, soulful, and tender.

"Sex that's born from an emotional place has an edge over other types of intimacy," says Gardos. "Because it involves a degree of looking at your partner in a new light, this sex feels like an expression of renewed love." But you don't need to experience a major event to tap into deeper emotions. It just requires a new way of looking at sex—one in which the orgasm isn't the most important thing. "It's about rediscovering and pleasing each other. Think sensual, not sexual," says Greer.

Here, foreplay takes center stage. Give each other head-to-toe massages; kiss each other's cheeks, ears, and necks; and pleasure each other orally. "The idea is to make your partner feel important, cherished, and valued," says Greer. Choose positions that allow for eye contact and a slow buildup to orgasm, such as sitting and facing each other or missionary. (For more ideas on this position, see page 104.)

"Inspire rediscovery sex every few months by making it a point to think about what made you fall in love and being open to learning something new about him," says Ogden. "Your partner can always surprise you—sometimes you just have to look for it."

Experimental Sex

Daring and boundary pushing, it's the kind of sex that benefits from familiarity and trust. You can break out the sex toys and indulge your fantasies without the fear of being judged. "At the core of experimental sex is novelty, and that's a huge arousal booster," says Gardos. "The more blood that rushes to your genitals, the better your orgasms will be." What's more, allowing your partner to see a secret side of you that no one else has access to builds intimacy.

So how do you suddenly start busting out sexual fantasies? You first have to have them. While you're lying in bed, standing in line at the grocery store, or walking to work, let your mind wander to whatever turns you on. It doesn't necessarily have to be stuff you want to act out; studies show that people who simply imagine sexy scenarios are more likely to experiment in bed.

When you want to make your fantasy a reality, broach it by saying something like "I had a dream you were doing A, B, and C to me" or "I read about this crazy move in a magazine. Want to hear it?" You can also shoot him an e-mail outlining what you want to do to him later. "Writing acts as foreplay for both of you. It forces you to think about what you're saying, which can increase arousal. And he'll be able to read and reread your message, which keeps sex on his mind," says Greer. But there's no better time to introduce something wild than in the heat of the moment; research conducted by M.I.T. and Carnegie Mellon University found that men are more likely to behave boldly when they're erect. (Shocker!)

"This type of sex is best saved for the weekends, particularly Saturday night," says Gardos. "You've left the stress of the week behind and you have the whole night ahead of you." Break out a spicy move once a month to keep things from getting stale.