People have a tendency to drink more on those days when they've indulged in some physical activity -- they drink alcohol, that is.

In a study from Northwestern University, almost 200 people aged 18 to 89 used a smartphone app and kept a diary daily to record their level of physical activity and alcohol consumption.

They kept track of both for 21 days during three study periods over a year, the researchers said. Their records showed they had a tendency to be more physically active and also drink more between Thursday and Sunday.

"Monday through Wednesday people batten down the hatches and they cut back on alcohol consumption," study author David Conroy said. "But once that 'social weekend' kicks off on Thursdays, physical activity increases and so does alcohol consumption."

It's not that active people consume more than inactive people, Conroy said; rather, "on days when people are more active, they tend to drink more than on days they are less active."

"This finding was uniform across study participants of all levels of physical activity and ages," he said.

Why people would drink more alcohol on days when they're more physically active is a question requiring more research, he said.

The researchers hypothesize that people feel accomplished after working out and celebrate by having more to drink. Physical activity could also occur in social settings where drinking alcohol is the norm.

He also raised the possibility that people who've used all their cognitive resources and willpower to push themselves to engage in physical activity are short of the willpower to resist the temptation of a celebratory drink at the end of an active day.

Beer appeared to be the favorite beverage after a workout or other form of elevated physical activity, the study found.

Insufficient physical exercise and alcohol consumption have been linked to a variety of health problems, but finding a way to enjoy the benefits of physical activity -- without experiencing the adverse effects of alcohol intake -- still requires further study, Conroy concluded.

The study was published online in Health Psychology, a journal of the American Psychological Association.

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