Unlike the U.S. Army, the British decided that lower levels of physical fitness for women soldiers was not acceptable and, since 1998, the women have had to meet the same high standards for physical fitness as the men. Since then, the army has learned the same thing the coaches of the increasingly popular women's sports program have; women are more prone to "overuse" injury. In some sports (like basketball) women have ten times the number of certain types of injuries (knees) as men. In the British army, even before the more vigorous training program for women, the percentage of male recruits lost because of "overuse injury" was 1.5 percent, versus 4.6 percent for women. The new training program, which does get the women in shape, also puts 11.1 percent of the recruits out of the service because of injuries. The basic problem is that less muscle mass and lower bone density puts 39 percent more stress on women during vigorous physical training. The army found that some of these injuries could be greatly reduced if the physical training for women was done over a six month period, rather than the current three month course men and women are using. But the injury rates will probably always be higher because of the fundamental gender differences.