The type of exercise did not seem to matter. Some happy people walked or jogged. Others practiced yoga-style posing and stretching.

And the amount of exercise needed to influence happiness was slight, Dr. Chen says. In several studies, people who worked out only once or twice a week said they felt much happier than those who never exercised. In other studies, 10 minutes a day of physical activity was linked with buoyant moods.

But more movement generally contributed to greater happiness. If people exercised for at least 30 minutes on most days, which is the standard American and European recommendation for good health, Dr. Chen says, they were about 30 percent more likely to consider themselves happy than people who did not meet the guidelines.

“I think the indications are strong that exercise can contribute to happiness and, while anything helps, a bit more is probably better,” she says.

But because most of the studies in this review were observational, she says, it is not possible yet to establish whether exercise directly causes changes in happiness or if the two just happen to occur together often. It could be that happy people are more likely to take up exercise and continue with it than people who feel sad. In that case, exercise would not have helped to make people happy; rather, their happiness would have helped to make them exercisers.

Happiness also is an inherently subjective, squishy concept. The studies analyzed in the review asked people how happy they felt. But one person’s happiness could be another’s relative gloom, making it difficult to generalize about how any of us might react, emotionally, to starting an exercise routine.

And, of course, the review did not delve into how exercise could be influencing happiness.

“There are indications that social factors could mediate the effects of exercise on happiness for some people,” Dr. Chen says. In other words, the social interactions that occur during an exercise class or trip to the gym might help to elevate people’s moods.