Researchers at Brigham found about one in five teenagers now have some degree of hearing damage. The researchers did not say why hearing loss has risen, but other experts have strong suspicions. One likely culprit, they say, is MP3 players.

An MP3 player can be dangerous to hearing when its decibel level is turned up too high. High-decibel sounds can damage nerve endings, called hair cells. If a sound is loud enough, the damage can be permanent. A loud sound can shake the membrane (薄膜) on which the hair cells sit- “like an earthquake”. That shake can break or even uproot hair cells. When that happens, the hair cells are finished. Human ears cannot regrow hair cells. Therefore, when listening to an MP3 player, set a volume limit and avoid exposure to loud sounds.

On the other hand, the loudness of today’s music may not be totally under your control. Music companies have been purposely turning up the volume. It’s a trend called the fight for loudness.

Play a CD from the 1990s. Then play a newly released tune. Don’t touch the volume control. You’ll probably notice that the new CD sounds louder than the old one. Why? Sound engineers who create CDs are using dynamic range compression (压缩), a technology that makes the quiet parts of a song louder and the loud parts quieter. The overall effect of compression is a louder recording.

Many musicians and sound engineers aren’t pleased. They say that compression is driving down the quality of today, s music, making it sound flat and blaring. Gray Hobish, a sound engineer, explains that music should be a combination of loudness and softness. But music companies want to make music louder so it will stand out. That’s important in the competition among recording companies.

What about listeners? Many teenagers listen to music on the go in noisy places and through headphones, all of which reduce sound quality. So young listeners may not notice the poorer quality of modem recordings. “To their ears,” says Hobish, “the music sounds fine. And they are not aware of the hidden threat of the music they are enjoying.”

Some experts say muscle loss begins around age 50. But others say it can start as early as age 30. Although muscle loss may be a natural part of aging , you can do some things to slow it down. Lost muscles are not gone forever. It is better to start building muscles when you are younger and in good health. Experts may not know exactly when muscle loss starts , but it is never too late to start strength training.

Simply put , strength training is what makes one's muscles stronger, Let us talk about some of the health benefits of strength training. This information comes from Harvard Medical School and the Mayo Clinic, a nonprofit health and research organization in the United States.

Harvard University researchers say that strength training puts pressure on your bones. This pressure can aggrandize the thickness or density of bones. This can reduce your risk of developing osteoporosis — a disease that weakens bones, making them easy to break, usually when people get older or because they do not have enough calcium or Vitamin D. And experts say strength training can reduce the problems of many long-term disorders, such as back pain, heart disease, diabetes and depression.

Considering it's easy for people to run to fat when getting older, strength training can help you take control of your weight. Muscle weighs more than fat. But muscle increases your metabolism （新陈代谢），and a higher metabolism helps you burn more calories.

Strength training can improve your ability to take activities. For example, having stronger muscles makes it easier to lift and move things. So, your risk of falling or getting injured may be lessened. As we age, this can greatly add to our quality of life. And some research shows that regular strength training, when combined with other kinds of exercise, may help older adults think and learn better.

The aging process affects the human body in many ways. It is believed that strength training can have a major effect on a person's life, so consider motivating others to join you in the many physical and emotional benefits of strength training.

We all know what a brain is. A doctor will tell you that the brain is the organ of the body in the head. It controls our body’s functions, movements, emotions and thoughts. But a brain can mean so much more.

A brain can also simply be a smart person. If a person is called brainy, she is smart and intelligent. If a family has many children but one of them is super smart, you could say, “She’s the brains in the family.” And if you are the brains behind something you are responsible for developing or organizing something. For example, Bill Gates is the brains behind Microsoft. Brain trust is a group of experts who give advice. Word experts say the phrase “brain trust” became popular when Franklin D. Roosevelt first ran for president in 1932, Several professors gave him advice on social and political issues facing the U. S.

These professors were called his “brain trust.” These ways we use the word “brain” all make sense. But other ways we use the word are not so easy to understand. For example, to understand the next brain expression, you first need to know the word “drain.” As a verb to drain means to, remove something by letting it flow away. So a brain drain may sound like a disease where the brain flows out the ears. But brain drain is when a country’s most educated people leave their countries to live in another. The brains are, sort of, draining out of the country.

However, if people are responsible for a great idea, you could say they brainstormed it. Here, brainstorm is not an act of weather. It is a process of thinking creatively about a complex topic. For example, business leaders may use brainstorming to create new products, and government leaders may brainstorm to solve problems. If people are brainwashed, it does not mean their brains are nice and clean. To brainwash means to make someone accept new beliefs by using repeated pressure in a forceful or tricky way. Keep in mind that brainwash is never used in a positive way.