When Nisha* landed a job as a part-time spinning instructor at a major franchise, she was excited to earn some extra cash.

She grew to love the community at her studio and the camaraderie with her colleagues. But there was one aspect of her new job that took her by surprise. “When I started training, I was shocked by how loud it was,” she says. The operators of the indoor cycling studio told Nisha “the louder the music is, the bigger the emotional impact in the room,” she recalls.

So she started cranking up the volume on the music in the classes she teaches every week. Now a couple of years into teaching, she’s not only grown accustomed to music at that level, she can’t hear music at lower levels as well as she used to. “I tend to max out my volume now both on the speakers and on my computer, which I did not used to have to do,” she told me. While she hasn’t yet had her hearing checked by an audiologist, she says she’s experienced some hearing loss from the noise at her job.

I spoke to five longtime exercise instructors — four who lead cycling classes and one who works at a gym — about their auditory health. Most of them did not want to reveal their identities because they feared they’d lose their jobs or because they signed agreements that they wouldn't speak with the media without permission. But they told a similar story: The noise levels they’ve been exposed to at work were high enough to make them concerned about hearing loss.

“There were days when I could come out of the studio after teaching a triple and my ears would be more sore than my muscles were,” one of the cycling instructors told Vox.

Dennis,* an instructor at a major spinning franchise who’s in his early 30s, became concerned about his hearing and went to an audiologist, who diagnosed him with early onset hearing loss. While the results of his hearing tests suggested genetics were mostly to blame, the audiologist said the five to 15 classes Dennis taught every week were certainly making things worse.

She also told Dennis to get custom earplugs, which cost several hundred dollars, to prevent further damage during his classes. When Dennis asked the management at his studio to cover the cost of the earplugs, they refused.

It’s not just the instructors who are at risk: Indoor cycling and gym clientele are exposed to the same dangerous noise levels — including me. I take classes at a major indoor cycling studio, Flywheel, so I decided to test the sound levels over the past several months. I consistently found noise levels that hovered over 100 decibels. That’s enough to violate the US Department of Labor standards for a safe noise environment, and to cause noise-induced hearing loss over the long term, which is why health authorities recommend no more than 15 minutes of exposure at that level.

When I told Flywheel about my findings, they said, “Flywheel is aware of its obligations to both its customers and its employees concerning appropriate sound levels in its studios and ensures that appropriate protective hearing measures are made available.” They declined to answer any further questions. SoulCycle also declined to comment for this story.

While noise levels can vary studio to studio, my readings squared with the findings from a 2016 study by otolaryngologists: In a random sampling of 17 classes at a variety of major spinning studios in the Boston area, the majority of class time registered over 100 decibels. The study authors did not specify which companies they included (for fear of any legal repercussions) but told Vox they covered six major US chains with locations throughout the US.

Check the noise levels at your exercise studio and submit them to us: Download a decibel-reading app like the NIOSH Sound Level Meter, SoundPrint, or Decibel X Pro and take a screengrab of the decibel reading in your exercise class. Submit them to us via email at julia.belluz@vox.com or tweet them using the hashtag #VoxNoisePollution.

Public health authorities are increasingly worried about noise exposure everywhere: The World Health Organization calls environmental noise an “underestimated threat,” and hearing loss (from all causes) is now the third most common chronic health condition in America, just after diabetes and cancer. One in four adults in America show signs of noise-induced hearing loss.

Yet many of us ignore the threat of noise — and are exposed to dangerous levels as we exercise and elsewhere in our lives — without protecting our ears. When I asked Nisha if she’s complained about the noise at her studio and the damage she believes it has done, she told me she hadn’t. Regulators and business owners also react with indifference.

This has to change. The case of loud cycling studios shows why.

A single 45-minute indoor cycling class was nine times the recommended noise exposure for an eight-hour workday

Since I started reporting a series on noise pollution, I’ve received hundreds of emails about all the places people feel their hearing is assaulting on a daily basis: in restaurants, in clothing and grocery stores, at the movies.

But many readers told me that exercise studios, and especially indoor cycling studios, are an increasingly common menace, perhaps because the the sector is booming and studios have popped up throughout the US.

Elliott Kozin, one of the authors on the Boston study of spinning studios and the chief resident in the department of otolaryngology at Harvard Medical School, said he was inspired to analyze the noise in spinning studios after he met two family members for lunch one day and they complained to him that their ears were ringing.

“I asked what they did, and they said they went to [an indoor cycling class], so I asked them how loud it was. They said it was deafening.”

So Kozin and his co-authors dispatched researchers to a random sample of 17 cycling studios in the Boston area. The researchers had high-quality decibel meters and made sure they attended classes at different times of the day and sat in different spots during each class.

Shockingly, they found that the average noise exposure for a 45-minute class was nearly nine times the recommended noise exposure for an eight-hour workday. And while you can find studies dating back to the ’90s in which researchers point out the paradox that fitness classes are probably also deafening their patrons, these noise levels were even louder than what’s been documented in previous studies, Kozin said.

The official government stance on safe noise levels comes from the National Institute for Occupational Safety and Health, which sets the standard for noise at work. It recommends limits of 85 decibels — a bit more than the loudness of a freight train 100 feet away — for eight hours a day, and that people exposed to anything louder use hearing protection.

Indoor cyclers who attend a single 45-minute class vastly exceeded their recommended dose for noise for an entire day, according to the study. “More importantly for the instructors, who may be doing two or three hour-long classes throughout the day,” Kozin said, “they are going to have considerable doses and be at risk for hearing loss.”

Federal health agencies are aware of the problem and planned to send out noise guidelines to exercise studios, but the project was halted

While Flywheel defended the loudness of its studios by saying it offers earplugs, most of the instructors I spoke to told me they didn’t wear them because it makes teaching to the beat of the music very difficult. Flywheel’s employee manual also says nothing about hearing damage. So the instructors are currently working in environments that are probably deafening them — and potentially their students too.

According to the Occupational Safety and Health Administration, which regulates workplace noise at the Department of Labor, “Workers have a right to a safe workplace,” and labor law “prohibits employers from retaliating against employees for exercising their rights under the law (including the right to raise a health and safety concern or report an injury).” OSHA handles workplace safety complaints on a case-by-case basis, and depending on the circumstances, employers can face fines for violating standards.

The National Institute for Occupational Safety and Health, part of the Centers for Disease Control and Prevention, is aware of the loud exercise class music problem. Its researchers were working with the authors of the study to come up with recommendations for how to prevent hearing loss that were to be sent to cycling and exercise studios — part of a “workplace solutions series” that offers public health guidance on safe workplaces. But in 2016, NIOSH decided to stop the project because of a reshuffling of research priorities.

“We expect to go to exercise classes to make ourselves healthier,” Kozin said. “What people don't quite think about is the fact that they might be hurting their health — hearing health — while they are exercising.”

He then used a secondhand smoke analogy. “It’s not that dissimilar to people who were bartending or being a waiter at a restaurant getting secondhand smoke — but instead, [these instructors are] having hearing damage.” What makes it worse, he continued, is that fitness instructors may think they’re working in a healthy environment.

How loud exercise classes can make us more vulnerable to noise-induced hearing loss

It is difficult to pinpoint the exact cause of noise-induced hearing loss since the effects of loud sounds on the ears are cumulative and can take years to show up in hearing tests. When and how quickly noise-induced hearing loss manifests in any person has a lot to do with their individual susceptibility. But the loud noises we’re exposed to can contribute to the wear and tear that degrades our hearing.

To understand how, we need to understand the machinery of the ear. We’re born with about 16,000 little hair cells in our ears that act as sound detectors. When sound waves pass into our ears, the hair cells send a signal to the brain, and then our brain decodes the sound, whether it comes from a barking dog or a truck that’s passing by. But “the brain’s interpretation is only as good as the signal it receives from the ear,” said Ellen Pfeffer Lafargue, an audiologist with the Center for Hearing and Communication in New York. “When the [hair cells in the] ear have been damaged, the sound that the brain gets is distorted or the ear can’t detect sound.”

Lafargue offered the analogy of a grassy meadow to help her patients understand how noise degrades hearing. “Imagine a field, walking through the grass. When you walk through one time and look back, you can’t tell anybody walked on the grass.” The blades recover and bounce up again. But “if you’ve walked through it enough times, it becomes a permanent path.”

The same thing happens with the ears’ hair cells. Like grass responding to a person’s feet, the hair cells bend when they’re exposed to loud sounds. They can bounce back during a recovery period — but when loud sounds have passed through the ears enough times, or at a high enough intensity, the hair cells get permanently destroyed. Along with them goes our ability to detect sound and send noise signals to the brain.

One symptom of noise-induced hearing loss is tinnitus, or ringing in your ears. The condition can be extremely bothersome, and while there are coping strategies, there’s currently no cure. (You can listen to sample tinnitus sounds here.) (One Pittsburgh-based exercise instructor I spoke to, Dana Sabo, and one regular indoor cyclist, Jane Langille, both said they think loud exercise classes contributed to the chronic tinnitus they now experience.)

What’s more, while being around loud sounds every day can certainly diminish your hearing over time, you don’t need sustained exposure to experience permanent damage. A single pop of thundering noise, like a gunshot or an explosion greater than 120 decibels, is enough to do permanent damage. So exposure to sounds at that level takes even less time to diminish hearing.

That’s why the World Health Organization and National Institutes of Health suggest people shouldn’t be exposed to noise at or above 100 decibels — where many exercise studios seem to operate at — for any more than 15 minutes. For noise at or above 110 decibels, these health authorities recommend no more than one minute.

Even more worrisome, Aaron Remenschneider, Kozin's co-author on the study and a researcher at Massachusetts Eye and Ear, said researchers are finding intense exercise can actually reduce the threshold at which noise can cause permanent damage. “While many people feel loud sounds and loud music may be motivational, we found there’s good data to suggest it can make people feel more apprehensive and reduce the threshold that patients ultimately have for their hearing loss.”

When I asked Remenschneider what he thinks studios should do, given the findings of his study, he said, “It’s fairly simple from our perspective: We’d just like for them to turn the volume down. That’s not a complicated algorithm for reducing the incidence of hearing loss in patients and instructors.”

How to protect your hearing

To protect your hearing, you need to understand how loud the environments you frequent really are. And to do that, there are now decibel readers you can download to your phone for free that let you measure the loudness around you.

Remember: Sound is made by waves of air pressure, and decibels are the unit by which sound intensity is measured. They fall on a logarithmic, or nonlinear, scale, meaning the marks on the scale are based on orders of magnitude. Every six decibels is perceived by the ears as about a doubling of loudness. So 96 decibels feels a whole lot louder than 90.

If you work at an exercise studio, you should speak to your management about the federal guidelines or file a complaint with OSHA. (To reach your regional or area OSHA office, go to the OSHA Offices by State webpage or call 1-800-321-6742.)

Or simply consider turning down the volume. A DC-based instructor, Dru Ryan, said he has noticed riders stick their fingers in their ears when he plays loud music, so he takes that as a cue that he needs to play the music a little quieter.

Students who frequent loud exercise studios should consider reporting the noise to the managers and making sure to wear earplugs, since they can attenuate noise up to 30 decibels. (Wirecutter recommends Mack’s slim-fit soft foam earplugs for their fit and ability to cut out noise, and the CDC has some advice about how to best insert them.) If your ears feel dull or they are ringing after the class, the plugs may not be strong enough and you may be damaging your hearing.

One of the audiologists I spoke to for this story, Leisa Lyles-DeLeon, told me she has at least one patient a week coming into her studio with noise-induced hearing loss who brings up exercise studios as a potential culprit. Which is why, at the Zumba classes she attends, she always wears earplugs and brings a pocket full of them, hoping that other students will ask her for a pair.

“The safest thing to do is to wear hearing protection and not depend on the studio to make the level it is for what they need to,” she said. But is also time for studios to acknowledge that they are contributing to the epidemic of hearing loss — and to do something about it.

Check the noise levels at your favorite exercise studio and submit them to us!

Download a decibel-reading app like the NIOSH Sound Level Meter, SoundPrint, or Decibel X Pro and take a screengrab of the decibel reading in your exercise class. Submit them to us via email at julia.belluz@vox.com or tweet them using the hashtag #VoxNoisePollution.