Jog bra or “sports bra” is a bra that provides firm support for the breasts. It is intended for wear during vigorous exercise that might cause the breasts to bounce around. In this way, it prevents discomfort and embarrassment during exercise. Sports bras are sturdier than regular bras and offer greater support for the chest, thus increasing comfort and reducing the chance of damage to the ligaments of the chest during high-impact exercises, such as jogging and running.
The first sports bra dates from 1977. Two women cut up a pair of jockstraps and sewed them together into a bra (Jogbra). Other designs use gel and water pads, silver fibres, and air bags. A stitchless bra was made by Wacoal, molded, compressed, and shaped. Other bras are knitted in circular patterns, giving varying stretch and support. A common basis is a stretchable, absorbent fabric such as Lycra, and may be designed to draw perspiration away from the skin to reduce irritation. Sports brassieres can be classified into either encapsulation brassieres (with molded cups), or compression brassieres that restrict movement by flattening the breasts. Encapsulation is generally better for reducing discomfort; some women prefer compression designs for modesty.
A number of women, particularly those with pendulous breasts, find sports bras helpful for easing pain and discomfort or if embarrassment prevents them from participating. Some sports bras are meant to be worn as outerwear, such as for jogging. Most bra research has concentrated on sports bras, where discomfort is directly related to the degree of nipple movement. While sports bras are more effective in this regard than standard bras, they also vary considerably in their effectiveness.
About 50 percent of women report some pain or discomfort in their breasts during exercise. This varies considerably in intensity and may depend on what they are wearing. In an Australian study 3 women (17-21, cup sizes B and C) were photographed exercising bare breasted, with two models of a bra, and with a particular sports bra. As expected, breast motion was reduced by bras, and the sports bra was the most effective. The women reported less discomfort with bras and especially with the sports bra. However not all sports bras are created equal and should be properly fitted. The more effective bras tend to be the least comfortable. Although some women athletes are concerned that a sports bra may interfere with breathing, and increased pressure on the rib cage has been demonstrated, no significant effect on breathing can be shown.