Middle market firms have remained resilient throughout the down economy, according to a study by Ohio State University's Fisher College of Business and GE Capital.

"As the U.S. struggles through the worst economic crisis in recent history, middle market firms are keeping local economies viable and represent the country's strongest engine for growth and long-term success," says Mike Neal, chairman and CEO of GE Capital.

The study also finds that middle market firms create $3.84 trillion in the U.S. private sector GDP, despite the stagnant growth. This is the equivalent of the world's fourth largest economy. In the next 12 months, 80 percent of middle market firms anticipate growth, and more one-third of U.S. employees work for the middle market.