"Athletic underwear" may be a generic term that refers to certain types of close fitting underwear suitable for athletic activities, or it may refer to sport-specific performance underwear designed with comfort and safety in mind. Very often, athletic underwear is made from synthetic materials that wick moisture away from the skin to keep the skin dry and comfortable; the underwear may also be made from a combination of synthetic materials and natural fibers. This type of underwear may be full-length underwear, or it may be cut for short sleeves and short legs.
The design of the athletic underwear will vary by gender as well as the sport for which the underwear was intended to be used. Athletes who play baseball, for example, may choose to wear sliding shorts, which are a type of athletic underwear designed to protect the thighs from abrasions when sliding into a base. For male baseball players, the shorts may also feature a pouch in which a protective cup can be placed. The design will differ for women, as the common body shape between the two genders will vary, though many of the same features will exist for both genders.
Long underwear is commonly used for skiing and other cold weather sports. This type of athletic underwear will be tight fitting to prevent movement restriction, and to encourage moisture-wicking. This means moisture is moved away from the surface of the skin, preventing chafing and rashes from developing. Keeping moisture off the skin will also help the person stay warm during inclement weather. Long underwear is also commonly used by hikers, backpackers, mountaineers, ice climbers, campers, and so on.
Cyclists can sometimes wear athletic underwear as well, though many cyclists wear Lycra® shorts that prevent the need for underwear altogether. When a cyclist does wear underwear, that underwear is usually tight fitting and it very often features a chamois pad in the seat to make sitting on a bike saddle more comfortable. Base layer shirts are very common among cyclists, as such shirts can help wick moisture, keep the cyclist warm in cooler weather, and help protect from the wind. Windproof base layers tend to be a bit thicker than other types of athletic underwear, but these layers are still thin enough to be worn underneath other layers of clothing. They are also usually moisture-wicking like other types of performance underwear.