The human temporary threshold shift after exposure to 60 minutes' noise in an aerobics class

The potential hazard of noise to hearing is well documented. However, there are some experiences of noise-induced hearing loss (NIHL) that are not so well-known, for example the effects of leisure noise, and in particular, leisure noise experienced during an aerobics class. A preliminary study of the noise level in aerobics classes in the Manchester region was carried out and their mean noise level was found to be 89.6 dB(A) (+/-4.7 dB(A)). Pure tone thresholds in the audible frequency range were obtained from 28 young adult volunteers (mean age 21 years; standard deviation (SD) 2.3 years) and 14 subjects (the 'exposure' group) were then invited to join (but not participate in) an aerobics class (mean noise level 91.8 dB(A) (+/-1.5 dB(A)) for 60 minutes. The noise levels in the aerobics class were monitored throughout the 60 minutes and the subjects did not stray from a small marked area (2 m2). Subjects' hearing thresholds were obtained for a second time, beginning within 2 minutes of the cessation of the noise, and any temporary threshold shifts (TTS) were noted. A second group of 14 subjects (the control group) was invited for a second audiogram after at least 60 minutes, during which time subjects were not exposed to any noise. The data obtained here were analysed and of the 14 subjects in the exposure group all had significant TTS at all frequencies except 1,000 Hz. Subjects in the control group, who had not experienced any noise, showed significantly reduced hearing thresholds (all frequencies; p>0.02), showing evidence of a possible practice effect with audiometric testing.