Do you work out hard and then party hard as well? Join the club.

People tend to exercise more than usual on the same days they drink more alcohol than usual, according to a new study published this month in Health Psychology and funded by the National Institute on Aging.

Researchers had 150 participants between 18 to 89 log their daily physical activity and alcohol consumption over a span of 21 days. The group did this at three different periods during the year.

Whereas previous studies had participants try to think back on their habits over a 30-day time span, or concluded that people who exercise more also drink more, this study zeroed in on individual, day-to-day behaviors. Participants were considered "low-risk" folks, who typically had a couple of drinks every few days.

"Something is happening on those days that's leading people to drink more," said David Conroy, the study's lead author and a professor at Northwestern University's Feinberg School of Medicine.

So what gives? Conroy said a number things could be at play. Perhaps people who like to work out also like to drink with the same people with whom they've exercised. Or maybe people are rewarding themselves for hitting the gym. Or maybe they've used up all the willpower they can muster to just get themselves to the gym, and they've got none left to refuse a drink later in the day.

Most of the alcohol consumption recorded by the study's participants came in the form of beer.

The "why" behind this exercise-drinking link will be the subject of future research, which could have an impact on how we go about encouraging exercise, Conroy said. "If we're going to promote physical activity,. . . we would be wise to think about whether there are any unintended consequences that could occur," he said.

The finding is unusual because healthy behaviors tend to cluster, and this is one of the few instances in which diametrically opposed behaviors (working out and drinking) are linked, Conroy said. For example, people who tend to exercise also tend to eat well and not smoke.

The link held for people whether they were younger or older adults. Researchers also attempted to adjust for the day of the week and the well-known "social weekend" effect which results in people drinking more Thursday through Sunday because their calendars allow for it. "It's not just that both are peaking at the same time," Conroy said -- but rather there is a link between the two behaviors.

Could it be that people are just trying to mitigate the calories they consumed from drinking the night before? Nope. Researchers found the link between exercising and drinking occurred on the same day, which they assume happened in that order. Given the effects of alcohol, "it seems unlikely that people would knock back a six-pack and then hop on a treadmill," Conroy said.