It's no longer enough to wake up on a Saturday morning and "run for fun." For event planning businesses to athletic apparel companies to hotels, this has become a great business opportunity.

Not only are running events booming across the country, themed road races are attracting droves of serious and not-so-serious runners looking for a new way to mix exercise with play.

The creativity is all over the map when it comes to these races. Some of the most popular include the Tough Mudder, a boot-camp like slog through muck and mud; the Color Run, a 5K race where runners throw colored powers on each other post-race; and the Rock 'n' Roll Marathon, a race where the course is lined with bands and cheerleading squads.

The growth of these races has been staggering. San Diego-based Competitor Group, the company in charge of the Rock 'n' Roll Marathon series, told U.S. News & World Report last year that the company has gone from five races in 2007 to 30 in 2013.

Each one of these races is a jolt to a host city's economy. According to the Washington Business Journal, 25,000 people were expected to participate in D.C.'s 2014 Rock 'n' Roll Marathon, with 80% of participants coming from out of town and will fill 18,000 of the city's hotel rooms. According to a study from San Diego State University, the 2013 version meant $22.8 million for the city.

D.C. is actually on the low end of the economic impact these races have for host cities. According to a study from George Washington University, the Rock 'n' Roll Marathon has had impacts of $183 million in Las Vegas, $39 million in Phoenix, $72 million in San Diego, and $45 million in Nashville.

The growth in themed races mirrors the growth in running over the past 20 to 25 years. According to a survey from Runners USA, the number of road race participants have tripled since 1990, with numbers of women growing more than sixfold over that period.

Large corporations have noticed.  Athletic apparel maker Reebok, subsidiary of Adidas AG (NASDAQ: ADDYY), has been trying to hone in on this market with slick ads that cater to a young demographic:

"We are really striving to show that fitness isn't something boring you do on a treadmill, or something solitary, like running alone," Yan Martin, Reebok's VP of global marketing, told MarketingDaily. "It's something that is very challenging, and involves a larger community."  

Walt Disney Corp. (NYSE: DIS) has followed that community ethos, holding a number of themed runs at its theme parks in Orlando, Fla. According to Esquire magazine, the company now organizes a weekend full of themed runs, with one marathon, five half marathons, a 10-miler, and two 10Ks. The event, with entry fees of up to $190, or $380 to run multiple events in one weekend, attracted 60,000 people in 2013.  

So while competitive marathons will never die out, a growing population of runners are looking for something different. Be it running through the Magic Kingdom or racing while rocking out, the numbers are clear that "running for fun" is a lifestyle trend that is becoming big business faster than you can lace up your sneakers.