Marriages tend to go flat. Doing something exciting together helps.

The wedding gets a year of planning. The marriage after it usually gets whatever time is left over.

That would be fine if marriages held their shape on their own. A long study suggests they tend not to.

The slide

Jody VanLaningham, David Johnson and Paul Amato followed a national sample of married Americans for 17 years, checking in five times. Earlier studies had suggested marital happiness dips in the middle years and rises again later. Following the same people over time, they found something less comforting: happiness tended to decline at every length of marriage, with no reliable rebound later on. The steepest drops came early and late.

That is an average, and plenty of marriages buck it. But it means the default direction is down, and holding steady takes some kind of effort.

What kind of effort

Arthur Aron and colleagues had a specific idea about why the early glow fades. In the first months, a partner is new, and being with them keeps expanding your world. Once that novelty settles, time together can turn into routine. Their prediction was that doing new and exciting things together could bring some of that feeling back.

They tested it in the lab. Couples were randomly assigned to a short task. Half did something new and a little ridiculous together: strapped to each other at the wrist and ankle, they crawled down a row of gym mats and over a barrier, carrying a pillow between them without using their hands, against the clock. The other half did a slow, ordinary task on the same mats, taking turns rolling a ball. In three experiments, the couples given the new and exciting task reported a bigger rise in how they felt about their relationship. In one of the experiments, all the couples were married. One short lab session was enough to see it.

Aron's group later described an earlier field study that ran longer. In it, married couples spent an hour and a half a week for 10 weeks on activities from a list. Couples assigned activities they both found exciting, like concerts, hiking or dancing, gained more in marital satisfaction than couples assigned activities they found pleasant, like dinner out or a movie.

Exciting activities, not just pleasant ones, are what moved satisfaction.

A later trial tested it on a larger scale. Kimberley Coulter and John Malouff randomly assigned 101 couples either to a four-week online program or to a waiting list. The program gave couples ideas and asked them to spend 90 minutes a week on shared exciting activities. Coulter and Malouff report that those couples afterward had more excitement in the relationship and higher satisfaction than the couples who were waiting, and four months later they were still above where they started.

Choosing the next thing

The line these studies draw is between pleasant and exciting. Your usual restaurant is pleasant. So is the show you always watch. Neither is a problem, and neither is what these studies found moving satisfaction.

Exciting does not have to mean expensive or extreme. In the field study, it meant things like concerts, lectures, hiking and dancing, picked from a list both partners had rated as exciting, and the online trial also asked couples for shared exciting activities. Only the lab experiments tested novelty directly, with a task that was new and a little arousing: a silly race on a gym mat.

So when the calendar opens up, try trading one usual evening for something you would both find exciting. If it is also new to both of you, like a class you would both be bad at or a place you have to find your way around, it is closer still to what the lab tested. It helps if you each name a few ideas and pick the overlap, the way the field study built its lists.

This is a different lever from how your partner responds to good news, which is about the conversations you already have. This one is about adding something to talk about.

What this does not show

The lab experiments measured how couples felt right after one short lab session, not months later. The field study was small, and the online trial followed couples for only four months. The field study also drew on upper-middle-class, middle-aged married couples in one California city. The 17-year study shows an average trend in US marriages, not what will happen in yours. None of this tests whether new activities can repair a marriage that is already in serious trouble.