By IHRSA's figures, of the 62.1 million Americans who used a health club last year, 9.2 million weren't members. Taking advantage of free trials and low-cost passes can keep costs low, and offer the ability to switch up exercise routines and work in more fun free summer activities like running or hiking.
For $85, the American Health and Fitness Alliance sells books of passes for fitness clubs in New York, Chicago, Houston and Los Angeles. And daily deal websites offer multiclass packages and one-month gym trials for as much as 85 percent off the going rate.
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Hopping around to try different gyms can also be helpful when it comes to picking the right one to commit to, said Mayor. Attendance rates tend to drop if a gym is more than 10 minutes from where a member lives. (See charts above for some of the most popular gym features and programs.)
Trial visits can also help you figure out how well a gym's value matches its price—Are you using all it its pricey amenities? Do crowds shut you out of popular classes? How often is the equipment out of order? "Make sure it's a gym that you're actually going to use," he said.
—By CNBC's Kelli B. Grant.