Above: 3 Star CrossFit in Mt. Juliet, Tenn., cut class sizes in half for social distancing and keeps garage bay doors open for air circulation since reopening in May.?

Owners try to balance state and medical guidance on face masks in the fitness studio; some let customers decide. ?The most frustrating thing is that there are no strict guidelines?

Gravity Fitness?in downtown Atlanta reopened May 11. Following new state protocols, a staffer at the gym?s entrance takes everyone?s temperature, and 6-foot spacing marks the gym floor, among other measures aimed at reducing the risk of spreading the novel coronavirus.

It didn?t take long, however, for gym owner Aaron Pols to realize Georgia?s regulations were insufficient. For starters, they seemed to require face masks for gym employees, but left them optional for customers.

?We have a lot of older members in their 50s and up, and they really didn?t feel comfortable without everybody wearing a mask,? Mr. Pols says. A few members who work for the nearby Centers for Disease Control and Prevention also voiced concerns, he said. ?Enough people spoke up that we needed to do something.?

So he made a new rule on the fly: Starting today, the gym will set aside a four-hour period, weekdays from 8 a.m. to 12 p.m., when face masks will be required for everyone. ?So people know what to expect,? he says. In its first week back in action, Gravity?s daily traffic was about half its usual 200 visitors a day.

New company safety protocols require instructors to wear a mask and goggles at Orangetheory Fitness Bearden in Knoxville, Tenn., since it reopened.

Several states?began easing some restrictions?in recent weeks to boost local economies?or at least slow their decline?amid the Covid-19 pandemic. Georgia, Oklahoma and Tennessee were among a handful of states to include gyms in the first wave of business reopenings. Safety protocols are set at the state and local level, creating a patchwork of regulations and uncertainty.

?The most frustrating thing is that there are no strict guidelines,? Mr. Pols says. ?They?re basically leaving it to the business owners, and unless you have a public health degree you don?t know what to do.?

The CDC has five local fitness centers for employees, and all remain closed. The agency follows federal rather than state guidelines, a spokesman said.

Gym-goers should be cautious about huffing and puffing in proximity to others indoors, says David Thomas, director of infectious diseases at Johns Hopkins Medicine. ?I would want the person working out next to me to be wearing a mask,? he said. ?We now understand that the degree of expiration, which is how hard you?re forcing air out of your mouth?to sing or shout or exhale?is a major factor in the amount of particles that get forced out of your lungs.?

Dr. Thomas suggests people weigh the risks before going to a gym. ?If you?re someone who has to touch every machine in the place, that?s a much bigger risk than the person who wipes down the one machine that they use, stays away from other people and gets in and out with minimal exposure,? he says.

Despite the?virus?s continued spread, some people are eager to get back to the gym. Denise Rowe, who runs a carpet-cleaning business with her husband in Knoxville, Tenn., used to visit Orangetheory Fitness Bearden five days a week until the gym closed in mid-March. Since its reopening on May 7, the 47-year-old has gone every other day. ?You might want to ask my husband, but I can tell you that my mood is 100% better since I?ve been going back,? Ms. Rowe says.

The state recommends?customers undergo a temperature check and a series of wellness questions. The studio cut class sizes in half, to 14 people, which allows for two empty rowing machines or treadmills between students, and changed class format so no one shares equipment, says Kelsey Forsythe, Orangetheory Bearden?s studio manager. Staff members do a deep clean of all equipment before and after classes. Lockers and showers are closed. The touchless water fountain is open; members need to bring their own water bottle.

A staffer does a temperature check, right, as a gym member takes a spray bottle of disinfectant, left, before a workout session at Gravity Fitness in Atlanta.

Orangetheory?s corporate guidelines for face coverings are more strict than Tennessee?s. Customers must bring their own face mask and wear it at all times, while instructors have to wear a face mask and safety goggles. ?We call our coaches little Minions because that?s what they look like,? Ms. Forsythe says, referring to the goggled characters from the ?Despicable Me? movies. ?We make the best of it and try to keep it fun.? Weekend classes have been fully booked, while weekday attendance has been mixed. Eight new members joined in the first week, a good number for this time of year, she says.

3 Star CrossFit in Mt. Juliet, Tenn., reopened on May 4, and while it has cut class sizes in half and mapped out 10-foot by 12-foot squares for social distancing, it is not requiring face masks. ?We?re doing everything that we have to do and leaving that decision up to members,? says trainer Emily Gillis. ?We?re in a big warehouse space and we?re keeping our two garage bay doors open to keep the air circulating, and we have an endless supply of approved cleaners.? They have also tweaked the CrossFit sessions so there is no partner work or equipment sharing. Showers and water fountains are closed.

?Our main demographic is soccer moms trying to stay healthy to play with her kids, and dads trying to defeat the dad-bod,? she says. The gym switched to an online reservation system, Ms. Gillis says, and average attendance last week was higher than normal.

Some large fitness chains, like Equinox and SoulCycle, have delayed opening locations nationwide, taking a wait-and-see approach. Gold?s Gym and Crunch Fitness, on the other hand, have reopened dozens of locations.

Class gets underway at 3 Star CrossFit in Mt. Juliet, Tenn. in May. State guidelines require disinfecting products be within easy reach for customers to clean equipment.

Crunch Fitness in Norman, Okla., reopened on May 4. Personal training director Troy Hail spent the prior weeks cleaning the facility, which was only a year old. ?We used industrial-strength sanitizer on every weight, took apart every machine, re-oiled or reupholstered, and we have a big section of turf that I cleaned with an electrochemical spray and vacuumed four times,? he says. The 27-year-old personal trainer says all five of his private clients have come back in the last week.

Oklahoma state guidelines?call for a temperature and wellness check at the door, but are less specific on face masks. Crunch corporate requires staff wear masks and gloves, Mr. Hail says. Though the gym recommends masks for customers, and even provides disposable ones, only about 10% of members are using them, he says, adding that gym traffic has been light, at less than 40% of capacity.

Every other cardio machine is roped off, all strength equipment is available, but there are no group classes. Showers are open; saunas, too, but limited to three people at a time, Mr. Hail says. For Dr. Thomas, though, saunas cross a line: they are tiny, closed spaces with little air movement.

Shauna Mazak is one of Mr. Hail?s clients. The 38-year-old respiratory therapist works nights in emergency and intensive care at Oklahoma?s OU Medical Center, and says the gym helps her keep her sanity. ?When you?re in the heart of it working 12- to 16-hour shifts, you just want a release?you need a place to go where you can burn off that energy you don?t think you have,? she says.

She didn?t know what to expect. ?This is a completely gray area that no one?s ever experienced before,? she said. ?But they have hand sanitizer everywhere, people are always cleaning. I?m very pleased with how they?re doing everything.?

By?Hilary Potkewitz for The Wall Street Journal

Click here for full podcast playlist.