About a quarter of the estimated 300,000 women infected with HIV in the United States suffer from muscle wasting related to infection with the virus. Testosterone replacement therapy has long been standard treatment for HIV-positive men, and now a new study finds that "replacing testosterone, the male hormone, improves muscle function in female patients" too, said lead researcher Dr. Steven Grinspoon of Massachusetts General Hospital.

A survey of teens found that males interested in physical intimacy push to have sex earlier, and females more interested in the emotional side want to postpone things.

"We see from these findings that this happens pretty early in life," said Nadine Kaslow, chief psychologist at Emory School of Medicine, who is familiar with the study findings. "If you think of [an adult] couple who has a fight, she'll often say, 'Until we're doing better, I don't want to have sex,' and he says, 'If we have sex, we'll be doing better.' Kids are showing you the exact same thing."

Researchers also found that teens treat casual sex differently than sex with potential partners, just like adults. And, in a phenomenon that may sound familiar to their elders, teens also promise themselves that they'll wait longer to have sex next time.

Perhaps surprisingly, sexuality researchers haven't spent much time studying how adolescents make sexual decisions.