Along with many other businesses, gyms across America were forced to close amid the Covid-19 pandemic. Now, as some start to reopen, they may struggle with getting members to come back, according to a new survey. 

In a survey published Thursday, online broker TD Ameritrade found that 59% of Americans say they don't plan on renewing their gym memberships once the pandemic is over.

The top reason? More than 56% of those surveyed say that the pandemic helped them find "more affordable" ways to get exercise and live a healthier lifestyle. 

TD Ameritrade surveyed 2,009 adults ages 24 and older with at least $10,000 in investable assets from March 4 -12 and April 24 - May 4. Of that group, 776 respondents said they lead a healthy lifestyle and exercise on a regular basis.

In the survey, respondents said they spent around $177 a month (or about $2,124 a year) on things like gym memberships, fitness classes and personal training.

Molly Passantino, senior retirement specialist at TD Ameritrade, says she believes Americans turning to cheaper fitness apps, outdoors activities like runs and walks and buying their own home workout equipment during quarantine likely caused the shift.

"There's also an element of uncertainty. Americans are likely questioning how gyms would work in the post-pandemic world. Will it be safe, will it be feasible to go?" Passantino says.

Despite the survey, Crunch Fitness CEO Jim Rowley, Crunch Fitness Worldwide CEO says the brand's gyms that have reopened are doing fine. (Crunch has 304 locations in the U.S., 169 of which have reopened.)

"Our workout volume [number of members coming in to workout each day] has been lower than last year, but our sales volume [number of memberships sold] has been higher and our cancels [cancelled memberships] have been relatively steady," compared to last year, Rowley tells CNBC Make It.

"So we're very encouraged by what we see as we've been able to reopen."

Rowley says he is discouraged that certain states like New York and New Jersey have not yet allowed gyms to fully reopen.

On June 26, New York Gov. Andrew Cuomo said gyms, malls and movie theaters will remain closed until the state Health Department determines whether air-filtering causes Covid-19 to circulate. While New Jersey Gov. Phil Murphy has not fully alllowed gyms to open, he has allowed individualized indoor instruction by appointment only and outdoor classes.

Rowley says Crunch conducted its own survey with 1,551 members in late April and found that 47% were dissatisfied with their at home workouts but 83% said they were likely to return to the gym when it re-opened. 

This story has been updated to include New York Gov. Andrew Cuomo and New Jersey Gov. Phil Murphy's comments on gyms reopening.

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