Diligently dragging yourself to the gym multiple times a week is supposed to have a positive effect on your overall health. According to an investigative report by Vox’s Julia Belluz, however, your choice of exercise might wind up doing more harm than good.

Indoor cycling, also known as spin class, has become a fitness staple in recent years, with people congregating indoors to ride stationary bikes at a tempo and pace set by an instructor. These sessions are often scored by music to help motivate participants. As Belluz found out, that music is sometimes so loud that it threatens to induce early-onset hearing loss in both trainers and trainees.

Belluz measured noise levels at her own fitness studio and found the volume to be in excess of 100 decibels (dB), a dangerously high register that exceeds Department of Labor standards and can be harmful to hearing if exposure lasts longer than 15 minutes. Her finding was in line with a 2016 study that took 17 audio measurements in the Boston area—including major fitness chains—and found that classes regularly rose to the 100 dB level.

Repeated exposure to loud noise can damage the hair cells in the ear that transmit sound to the brain, an injury analogous to grass being bent as it’s being continually walked on. Eventually, the hair cells—like the grass—fail to spring back, leading to hearing loss.

Currently, no workplace safety authority (OSHA, National Institute for Occupational Safety and Health) has made any specific spin class-related mandates, though individual sites may face a fine if they’re reported. The best way to mitigate a chance of damage to your hearing is to take sound measurements with a smart phone app and confirm your class isn’t in the 100 dB level. If you’re concerned about the volume, talking to management or wearing earplugs can help buffer the noise pollution.

[h/t Vox]