I appreciate the many thoughtful and enlightening comments to my earlier post. Many of the issues raised are matters I am writing about in this post or in subsequent ones.
Advocates of integration of women into combat forces often downplay the sex difference in physical capacity, correctly pointing out that some women are stronger than some men. In fact, however, there is little overlap between the sexes in terms of strength.
Women, on average, have only one-half to two-thirds the upper-body strength of men. The probability that a randomly selected man will have greater upper-body strength than a randomly selected woman is generally between 95 and 99 percent, depending upon the measure and the sample. Most of this difference is due to differences in the quantity of muscle tissue, a difference attributable primarily to sex hormones.
Although most discussion of physical sex differences focuses on strength, the sexes also differ on a host of other performance measures, such as running speed, aerobic and anaerobic capacity, endurance, and throwing speed and accuracy. These abilities are all potentially important in combat.
Some assert that these large physical differences can be overcome through training. In fact, however, training often increases the sex difference. Both sexes benefit from strength training, and in samples of out-of-shape individuals, women may initially gain more from training than men. Nonetheless, the overlap between the sexes decreases, because training not only increases the strength of both groups, it also decreases the variability within the groups. When males and females both start out in good physical condition, women gain less from further conditioning than men do, so the gap between the sexes actually increases.
Related to differences in strength and bone mass is the high rate of injuries, especially stress fractures, suffered by women in physical training. An extensive study of physical capacity by the British Ministry of Defence concluded that only about 0.1 percent of female recruits and 1 percent of trained female soldiers could satisfy the required physical standards for infantry and armor without sustaining substantially higher rates of injuries than men.
Much of the momentum for sexual integration of the combat arms rests on the assumption that the substantial sex differences in physical capacity, while real, are no longer significant, because battlefield prowess is now