Anal sex can hurt, that much seems clear. But a new study of British teenagers also reveals a few aspects of this sexual activity that are perhaps more surprising.

The researchers interviewed 130 teens ages 16 to 18 from diverse backgrounds, and asked them about their perceptions of different sexual practices, as well as their own experiences. The results showed that most teens' anal sex experiences occurred in a relationship setting, but first experiences with anal sex were rarely under circumstances of mutual exploration of sexual pleasure.

Instead, it was mainly men who pushed the women to try anal sex, and men said they felt expected to take this role. Moreover, the teens expected men to find pleasure in anal sex, whereas women were mostly expected to endure the negative aspects of anal sex, such as pain or a damaged reputation. [Hot Stuff: 10 Unusual Sexual Fixations]

Young women in the study reported anal sex as painful, but at the same time, the majority of teens saw women's experience of pain as due to women being "naïve or flawed," and unable to relax, the researchers said in their findings published today today (Aug. 13) in the journal BMJ.

The results also revealed somewhat surprising, and in some cases concerning, aspects of anal sex. However, the findings may not be generalizable to all populations, because they are based on a small study of heterosexual teenagers.

Men compete with each other to have anal sex

Young men in the study appeared to perceive having anal sex as a feat in competition. Even though not all the young men in the study said they wanted to have anal sex, many of them said men encourage one another to try the practice. In a group discussion as part of the study, young men said anal sex was something they do for competition.

But both men and women said anal sex could damage women's reputations.

A lot of guys didn't really like it

Young men in the study were often keen on the idea of anal sex, but were sometimes unenthusiastic about the physical reality, the researchers said. For example, one interviewee said: "I thought it was going to be a lot better to be honest."

Only one young woman in the study stated slightly positive feelings about having had anal sex. Although she said she was persuaded by her partner to engage in anal sex, she also told the researcher that she was curious about trying it, and had enjoyed her experience.

Normalization of coercion?

The researchers found that the teenagers thought women would generally be reluctant to have anal sex, and would participate only if persuaded, or even coerced into it, and that the act might hurt them.

The researchers wrote that it seemed women commonly saw their role as accepting or declining their partner's request for anal sex, rather than being an equal decision-maker about this sexual activity.

"It seemed that men were expected to persuade or coerce reluctant partners," the researchers said.

However, the researchers noted that some young men in the study did say they avoided anal sex because they believed it might hurt their partners.

'It slipped'

In some cases, teens reported that anal penetration happened accidentally, because they "slipped." But in one case, a male teenager corrected himself in a second interview, and said that what he had initially referred to as an accident was in fact no accident after all.

"It is difficult to assess the extent to which events described as 'slips' were genuinely unintentional," the researchers said.

The researchers said describing events as "slips" may enable men and women to avoid confronting the possibility that a non-consensual penetration was deliberate.

Teens don't know they can get STDs from unprotected anal sex

The researchers found that many interviewed teenagers didn't know it is possible to get a sexually transmitted disease (STD) from unprotected anal sex. Some actually said that getting an STD via anal sex was impossible, or less likely than for vaginal intercourse, according to the study.

The researchers also found that condoms don't seem to be a frequent element in anal sex, and when they were used, it was for hygiene purposes not STD prevention. [Quiz: Test Your STD Smarts]

Porn is only one factor behind anal sex

Participants often mentioned that young men want to have anal sex with women because they want to copy what they saw in pornography. But the researchers said pornography appears to be only one factor in why teens may have anal sex, and the new findings suggest there are also other explanations and motivations involved.

"Current debates about young people's sex lives often seem to focus narrowly on the impact of porn," said lead author Cicely Marston, senior lecturer in social science at the London School of Hygiene & Tropical Medicine. "But our study suggests we need to think more widely about the lack of importance society places on women's rights, desires and concerns."

Email Bahar Gholipour. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.