They're not always on the friendliest of term.

Let's face it: a woman's breasts were not made with running and jumping in mind. That's not to say that women weren't meant to exercise, but that our breasts need a little extra protection when we do.

A recent study found that 56 percent of women experience breast discomfort while exercising. Certain sports also present the risk of injury: The breasts' rich vascular supply makes them particularly vulnerable to internal bleeding from impact with a ball or another person.

Fortunately proper care can prevent or alleviate many problems. Especially important is wearing the kind of sports bra that's right for you.

A woman's breasts are chiefly composed of hormone-sensitive mammary glands, fatty tissue and connective tissue. The pectoralis major and minor muscles lie underneath the breasts, but the breasts themselves have no true supporting ligaments or muscle tissue. Therefore, excessive motion during sporting activities may cause pain and aggravate sagging or stretch marks.

Excessive breast motion and discomfort can be controlled by wearing either a supportive or compressive bra. A compressive bra, which functions like a binder; is better for a woman with small breasts (A or B cup size). A woman with large breasts (C cup size and larger) needs a firmer, supportive bra that encapsulates the breasts individually. An Ace-type elastic bandage wrapped around the chest over the bra, to compress the breasts, may also be helpful.

There are many athletic bras on the market, but not all of them meet the needs of an active woman. The best way to judge a bra is to try it on and jump and jog in front of the changing-room mirror, watching for excessive breast motion. You may feel a little silly but you'll be less likely to end up with an uncomfortable, ill-fitting bra.

What determines your breast size?

What determines breast size

After puberty all women have essentially the same amount of glandular tissue in their breasts. Differences in breast size are due mainly to fatty tissue and the response of the glandular tissue to hormones.

Lean athletes usually have smaller breasts because of their overall lower percentage of body fat. Increasing body weight may increase the fat in the breasts. Most athletes do not want large breasts, however.

Contrary to many popular advertisements, you cannot enlarge your breasts with topical creams or "breast development" exercise devices. Exercise can only develop the underlying pectoral muscles, not the breasts themselves.

Any woman who does want larger breasts should be aware of certain drawbacks associated with surgical breast augmentation, especially if she's athletic. The implants are either silicone or saline filled bags, which can rupture with a direct blow. They can leak silicone, or the tissue around them may become infected. Also, large breasts can adversely affect performance, especially for swimmers who will have extra drag in the water.

The mammary glands are very sensitive to female hormones. A woman may experience an increase in breast size premenstrually or with certain oral contraceptives. During pregnancy and lactation, all women's breasts enlarge. Use of androgens and anabolic steroids will decrease breast size.

Am I normal?

Women concerned about breast size should be aware that size does not affect sexual arousal or the ability to nurse children. Since all women have the same amount of glandular tissue, the breasts will respond appropriately for lactation no matter what their size.

Is it normal for one breast to be larger than the other?

It is very common - and completely normal - for one breast to be slightly larger than the other. Normal nipples may be inverted, everted or flat and have a few hairs. However, if you are not pregnant or lactating, any breast discharge is abnormal and should be brought to the attention of your physician.

Common breast injuries

Nipple burn, caused by abrasion of clothing, can result in painful blisters and bleeding. It occurs in men as well as women.

To prevent abrasion, apply a lubricant, such as Vaseline, and cover the nipple with a Band-Aid or gauze pad anchored with porous paper tape. Commercial products such as Second Skin or Nu Skin are also effective.

Bicyclists can get a painful cold-induced nipple injury resulting from the combination of perspiration and wind chill. This can be prevented by wearing evaporative materials in bras and clothing, plus layers of insulation and a windbreaking jacket.

Cotton and cotton/polyester bras may aggravate nipple burn. Cotton/polypropylene seamless bras work best to facilitate sweat evaporation and limit chafing.

Any nipple injury can easily become infected and should be treated with a soothing antibiotic cream.

Internal bleeding is another common breast injury. It is usually caused by a direct blow in contact or racquet sports or by impact with the ball in games like softball and soccer.

Discontinue play if you suspect internal bleeding in the breast. Promptly apply an ice pack and compressive dressing (such as an Ace bandage wrapped around the chest). Carefully clean any break in the skin with an antibiotic solution such as Betadine.

What should you do if you think your injury needs stitches?

See a physician immediately if there is any question of needing stitches (sutures should be in place within 12 hours). If you have a deep wound, you may need to have the blood removed by aspiration, and your physician may prescribe antibiotics to prevent abcess formation.

This type of injury is very painful. You may need analgesics and supportive dressings or bras for several days. To decrease the pain and swelling from a bruise, use ice packs tucked in a supportive bra for 10 to 15 minutes every few hours over the next few days. You might also find it more comfortable to sleep wearing a support bra or compressive wrap.

Don't return to action until you are almost pain free and there is no sign of infection. If you have had stitches, wait until they are removed before you resume exercise. Excessive motion of the breast will delay healing and lead to larger scar formation.

Contrary to some beliefs in both the medical and lay community there is no relationship between injuries and breast cancer. In fact, retrospective surveys have found that collegiate women athletes have a lower incidence of breast cancer and cancers of the reproductive system regardless of injury than non-athletic women.

For your own peace of mind, every woman should know how to do breast self-examination and perform it regularly just after her period ends.

About the authors: Carol L. Otis, M.D., is Chief Medical Advisor to the Sanex WTA and UCLA student health physician. Roger Goldingay is a former professional soccer player. They are married and the co-authors of The Athletic Woman's Survival Guide.