If you feel underpaid, you may want to hit the gym. You'll feel better immediately, and over the long term you'll get better pay.

That is the implication of a new study in the June issue of the Journal of Labor Research, according to SmartMoney. The study found that workers that exercise on a regular basis earn 9 percent more than inactive workers.

Vasilios Kosteas, economics professor at Cleveland State University and the study's author, told SmartMoney that his study shows that exercise leads to higher pay, since the study compares workers with a similar propensity to exercise.

Attractiveness is associated with higher pay, according to several studies. For women, obesity is associated with an 18 percent wage reduction, one study found.

Some workers may really need the exercise. Fourty-four percent of workers have gained weight in their current job, according to a recent study by CareerBuilder. Jobs that make people gain weight include law, social work, teaching, and public relations.

Exercise makes us happier, healthier, more attractive, and even smarter, according to several studies.