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Abstract: Some safe sound facts for exercisers and instructors in aerobic classes.

Key Words: dangerous sound, aerobics classes, sound standards, loud music, hearing damage, hearing protection, exercise environment, American Council on Exercise,

Staying fit includes exercise: lifting weights, bicycling, swimming and aerobics classes. Lifting, bicycling, and swimming are managed in pleasant healthy surroundings. Aerobic classes are another matter. The exercise is healthy but the music level is not. The rise of deafness among young persons and concern for the hearing of aerobics instructors and students led the American Council on Exercise, (ACE), the professional organization for aerobics instructors, to recommend guidelines for safe music volume in fitness settings. Aerobics classes at three fitness clubs in Northern Virginia were sampled searching for a safe level of sound. ACE's guidelines, which match standards set by the Environmental Protection Agency, are largely ignored. It is almost impossible to find a class that does not involve dangerously high sound intensity. Typically the instructor revs up the music, sets the neck mike above the music and overloads the amplifier. As a result, exercise commands are delivered with lots of high frequency static destroying the consonants. The instructor solves this problem by shouting into the neck mike making the situation worse. Sound intensity levels, I have measured in these classes, are close to that of a jackhammer, definitely unsafe. When instructing clients in lifting weights, personal trainers are very watchful insuring that a client will not sustain muscle tears but there is no way for an aerobics instructor using sound to monitor damage to the ear. That is why ACE has set acceptable sound levels for their instructors and classes to a level below ear damage standards set by EPA.

Sound intensity, the amount of energy reaching your ear each second, is measured in decibels, dB. Normal conversation is about 50-65 dB, busy traffic noise is 70 -80 dB, and a jackhammer is 90 -120 dB. Sound you can barely hear, is called the threshold of hearing and is labeled 0 dB. At 0 dB your eardrum is sensing a pressure only about 1 billionth more than atmospheric pressure. The safe level of a sound depends on how long you are exposed to it. At 85 db the EPA standard for safe sound is 45 minutes. ACE's certification guidelines for aerobics instructors and their teaching facilities state that sound levels for aerobics classes should be in the range of 70-80 db, a level, which insures the use of EPA standards in exercise classrooms.

When the barely audible sound level of 0 dB hits your ear, your eardrum vibrates with a very small motion-less than the diameter of an atom. The dB scale is logarithmic. For example, at 100 dB the sound intensity is not 100 times the threshold of hearing but 10 billion times. At 100 dB your delicate eardrum is swinging over a distance billions of times greater than at the threshold of hearing. A walkman can produce 100 dB directly into your ear canal.

The vibration of the eardrum is translated to a set of three delicate bones in the middle ear. The deepest of these bones is attached to a window (membrane) in the middle ear. This window sends the vibration to the fluid filled inner ear. (In the ear canal sounds in the range of 2-5 KHZ, the upper notes on the piano, are boosted by 10 dB). The inner ear processes loudness and frequency information to the brain via delicate hair cells. Under exposure to loud sound, hair cells can break, fuse, or disintegrate. Holes can appear in the membrane, which holds the hair cells, and information traveling to the brain is lost. Under acoustic trauma, such as an explosion, the damage can happen instantly. With regular exposure to loud recreational sound, such as aerobics classes or rock concerts, it happens more slowly. A curious fact is the division of labor among inner and outer hair cells. The outer hair cells detect soft sounds, but the majority of nerve fibers going to the brain are attached to inner hair cells. Inner hair cells control the information from loud sounds. So if outer hair cells are damaged soft sounds will be lost but loud sounds may still be heard as easily as before. Hearing aids, which amplify sound so that soft sounds can be heard, will make loud sounds too loud. The result is the wearer is very uncomfortable. The first loss in hearing is usually in the high frequencies. These are very important frequencies because they shape the consonants. Vowels are shaped by low frequencies. When measuring for hearing loss, audiologists test very carefully the ability to distinguish s, f, t, p and k. For a 30 year old a hearing loss of 15 dB at these consonant frequencies means your ears have aged 20 years. High frequency sounds such as static are more damaging than low frequency sound splayed at the same intensity, add 5 db to get the equivalent hazard level.

Hearing loss is not the only problem. ACE has also documented that fitness instructors are damaging their voices from shouting over music levels.

At the start of the quest for a safe aerobics class I brought a sound level meter, called a dB meter to my favorite aerobics activity, spinning classes. I found the sound intensity level in classes typically registered 100-110 dB, 30 -40 dB above ACE guidelines. I quizzed fitness and membership staff about sound safety guidelines. At one national club the membership staff looked blank and were unable to find any guidelines for sound levels. Worse was the attitude at another club whose sales staff politely walked me out the door when I asked what the maximum sound level in class would be. Finally, a friend persuaded me to join his club where he was a staff member. He promised safe sound measured with the club meter. I believed him, signed up and made a financial commitment. At my first spinning class I realized that sound was unsafe, and asked the instructor to lower it. She rudely invited me to leave. I asked for a meter. The truth was the club did not own a meter. However the head aerobics coordinator produced the club's national guidelines for sound levels. I found I'd joined a club where instructors were allowed to teach with the sound at 110 dB. I protested to both the aerobics coordinator and individual instructors. Most instructors resented the intrusion of a safety consideration into their routine and when asked to turn the sound down to the ACE guidelines suggested that an aerobics class was not for me. The excuses ranged from 'other students demand high levels of sound' to 'it's impossible to exercise at a high level without high level sound'. In reality, I felt it was the instructor who wanted to exercise to music at this level. A pow-wow between our local aerobics coordinator and the national aerobics coordinator about safe sound levels almost became contentious. Neither woman was interested in safety but only in forbidding me to measure levels in my classes. According to ACE guidelines all clubs are required to measure sound levels and suggests each room have a sound level meter for continual monitoring. Knowing that the club was in violation of ACE guidelines, I wrote the club's national headquarters. I never received a reply but a month later new sound guidelines were issued lowering the intensity to 90 dB, closer to ACE standards. Regrettably the new guidelines did not insist on furnishing the classroom with a dB meter. Teaching aerobics at high sound levels is a learned behavior and most instructors are unwilling to change. Most instructors cannot distinguish dangerous sound levels without a meter. Hoping that education would persuade, I distributed a safe sound hearing guide to all instructors. This was generally useless, as one instructor explained 'I believe you but I'm a young person', others jokingly? admitted that their hearing was already damaged. Only one instructor understood the danger of unsafe sound; one of his best friends teaches at a school for the deaf. I'm still a member at this club but I've learned either to bring in my own sound level meter or ask the staff to monitor the intensity.

How to improve your exercise environment? What to watch for: symptoms of dangerously loud sound. If, after class, your ears are ringing it's a sign the music was too loud. Tinnitus, ringing or buzzing in the ears is usually a symptom of acoustic trauma. Another symptom identified by health professionals is threshold shift. It's easy to recognize. If you listen to your car radio after an evening aerobics class and then are surprised the next morning at how loud the volume is, this is a sign that after class you suffered from a temporary threshold shift, TTS, and you are on the road to permanent threshold shift, permanent damage. Certain anticancer drugs and antibiotics can cause hearing loss and these drugs combined with loud sound can enhance the hearing loss.

How can you protect yourself? You can wear earplugs, the cheapest, foam cylinders, are sold in drug stores. Their manufacturers claim they will reduce the sound energy level at your ear by 30 dB. However, they must be compressed by rolling very tightly so that when inserted they expand to fill the ear canal. Molded plugs worn by entertainers and sound technicians contain active elements and are advertised as providing musical fidelity and reducing sound intensity by 30 dB. But the most effective way is to buy a dB meter, carry it to class and insist on sound levels no higher than 85 dB. dB meters are available from half a dozen professional equipment firms, the cheapest being about $59.00. Buying a dB meter is a small investment compared to the cost of hearing aids. Good hearing aids, cost thousands of dollars, are not covered by most health insurance or Medicare and can never come close to replicating your ears.

How to insure a good relationship with your instructor while protecting your ears? Get to class a few minutes early, ask the instructor to set the neck mike so that commands can be understood and set the music level under this. Finally measure the level with your dB meter. Some fellow students might object and pressure the instructor to raise the level. This has happened to me. It's like being a non-smoker in a room of smokers. At this point the responsible instructor will inform the class about hearing safety. You can also ask your local governing body about legal restrictions. Sound ordinances in Fairfax County, Virginia, restrict the sound level in public settings to 90 dB and in residential settings to 55 dB. Places of public entertainment and assembly which exceed 90 dB are required to post a warning sign outside stating: that the sound environment may cause hearing damage. Last summer while I was attending a performance at The Wolf Trap Center for the Performing Arts, in Vienna, Virginia, the performer requested his sound engineer to up the sound to a level at which we could feel facial pressure. But the ushers were prepared for such a situation. As many of us fled the venue, they offered us earplugs. If a warning sign had been posted at the entrance we would have asked for our money back. Unfortunately a couple with a baby seated in the front row remained, unaware of the danger to the infant.

People engage in all sorts of unhealthy practices, smoking, exposure to the sun without sunscreen, not using sunglasses to cut down exposure to cataract causing ultraviolet radiation, and listening to loud music. Some religious sects even stare at the sun claiming it energizes them. There is no reason to encourage any one of these practices. Your ears are your own, incredibly delicate and sensitive detectors. If you were asked to exercise or attend a concert in a setting where the level of radioactivity was hundreds of times higher than the allowable doses set by the National Radiation Protection board, I'm sure clients would be demanding the facility be shut down Yet this same situation exists in group exercise settings, the only difference is: in the aerobics class the radiation is of the acoustic variety and the affected organ is very specific, your ear. There can be no reason, which entitles clients at a fitness club to exercise at the same sound levels they insist on in rock concerts. It is reasonable that the safe standard to adopt would be based on the information from EPA. We have learned to keep our lungs healthy, we can learn to treasure our ears.

Sound Facts and Resources:

According to The National Health Interview Survey hearing problems of Americans between the ages of 45 and 64 increased 26 percent between 1971 and 1990. Amongst younger persons, 18-44, hearing loss increased 17 percent. These facts have initiated the passage of local ordinances, which govern sound levels in recreational settings for many American communities.
At 85 db the EPA standard for safe sound is 45 minutes. At 88 db the EPA standard for safe sound is 23 minutes. EPA regards 91 db as unsafe for any length of time over 11 minutes. The European Union has set the maximum legal limit for recreational sound in its member countries as 85 dB with a suggested level of 80 dB.
Acoustic trauma occurs at 180 dB, which is equivalent to a pressure of about 2-3 lbs per square inch on the drum. At 120 db the bones of the middle ear vibrates so strongly they strike the middle ear wall. These bones amplify the force on the window into the cochlea to 15 times the force on the eardrum. No medical intervention is possible to correct hearing loss due to loud sound or acoustic trauma.

Web site resources:

American Speech-Language-Hearing Association Information on preventing hearing loss and tinnitus
Noise Pollution Clearing House Lists the standards set by EPA
National Institute on Deafness and other Communication Disorders NIH website with important links for parents and musicians
Hearing Education and Awareness for Rockers H.E.A.R. A non-profit hearing information source for musicians and music lovers
Deafness Research Foundation A non-profit foundation sponsoring education and research in hearing science .
American Council on Exercise A non-profit fitness certification and education provider
Test Equipment Depot A source describing dB meters.

Paper Resources:

The Noise Manual, E.H.Berger, L.H.Royster, J.D.Royster. D.P.Driscoll, M.Layne Eds (2000) AIHA PRESS Physics (3rd ed.) J.W.Kane, M.M.Sternheim (1988) John Wiley Physics with Applications in Life Sciences G.K.Strother (1977) Houghton Mifflin

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