By Jack Hough | SmartMoney – Thu, Jun 7, 2012 1:08 PM EDT

Stagnant wages and shaky investment markets are enough to make workers want to hit the gym to forget about their money troubles. They might just find that the treadmill offers better financial returns than Wall Street.

Workers who exercise regularly earn 9% higher pay on average than those who don’t, according to a study published in the June issue of the Journal of Labor Research.

Past studies have linked exercise with higher earnings, but the direction of cause and effect wasn’t clear. If gym-goers are more disciplined than their slothful coworkers, they might earn higher pay simply because they’re better workers, not because they exercise.

In an effort to cut through the confusion, Vasilios Kosteas of Cleveland State University, the study’s author, used a statistical technique called propensity-score matching. The idea is to score each study subject on whether they fit the profile of someone who exercises, based on factors like age, education level, and whether he or she played sports in high school.

By comparing subjects with similar scores, only some of whom exercise, Mr. Kosteas says his study indicates that exercise leads to higher earnings — although he also says follow-up studies are needed to know for sure.

Exercise has been shown in other studies to boost mental function and energy levels and improve mood. In that respect, it’s possible that it makes workers more valuable to employers.

If it’s any motivation for workers, the study suggests time at the gym pays for itself, and then some.

In May, the average American worker earned $23.41 an hour, according to the Labor Department.  Assuming three hours of exercise per week, enough to satisfy the minimum level used in the study, a typical worker’s time spent huffing and puffing is valued by the labor market at $70.23. His extra pay over a 40-hour work week is worth $84.28–about 20% more.

Of course, even if the study findings hold for large numbers of people, there’s no guarantee an individual’s workouts will lead to a raise. But it may bring other financial rewards, like lower healthcare costs and the ability to remain productive into old age.

Mr. Kosteas takes his own investment advice. At 5’6” and 165 pounds, he says he lifts weights regularly–even if he has put on 10 pounds since the birth of his son. Two years ago he got a promotion and a raise.