Traditionally, the American male was measured against the stoic hero who shook off all doubts, vanquished all foes and offered women a muscular shoulder to cry on.
But that was before feminism, gay-rights activism, metrosexuals. Husbands took on a greater share of housework and child care. The military welcomed women and gays. A romantic movie about gay cowboys, "Brokeback Mountain," won three Oscars. And last week, the ground shifted under the hyper-masculine realm of America's most popular pro sport - the NFL, it seems, will soon have its first openly gay player.
Off the playing field, in their daily lives, countless American men are trying to navigate these changes. For some, it's a source of confusion and anxiety.
"Men are conflicted, ambivalent," said James O'Neil, a psychology professor at the University of Connecticut who has written extensively on men's struggles over gender roles.
"On one hand they've been socialized to meet the old stereotypes," he said. "On the other hand, particularly for men in their 30s and 40s, they begin to say, 'That's not working for me. It's too stressful.' They're looking for alternative models of masculinity."
But for other Americans, the upheaval is a good thing.
"Ultimately, confusion about modern masculinity is a good thing: It means we're working past the outmoded definition," wrote journalist and blogger Ann Friedman in a nymag.com article last fall titled "What Does Manhood Mean in 2013?"
After World War II, at least on the surface, there seemed to be an overwhelming consensus of what American manhood was all about. It was typified by Gary Cooper and John Wayne on the movie screen, by the GIs on America's foreign battlefields, by the executives with homemaker wives and no corporate worries about gender diversity.
The feminist movement that emerged in the 1960s fractured this consensus and fueled significant, though gradual, changes in many Americans' perceptions of gender roles and stereotypes. By now, although women remain underrepresented as CEOs, they comprise close to half the enrollment in U.S. medical and law schools and are being welcomed into military combat units.
Over the same period, perceptions of manhood and masculinity also have evolved. Surveys show that husbands are handling far more housework and child care than they used to, though still less than their wives. Soccer icon David Beckham proved that a male sports star with a celebrity wife could embrace nail polish and flamboyant fashion without losing his fans.
"The women's movement showed that women didn't want to be restricted by their gender role, and it's opened things up for men to not be restricted as well - they can be stay-at-home dads, they can be nurses," said Bonnie Grabenhofer, a vice president of the National Organization for Women. Though from her perspective the pace of change has been "agonizingly slow."
Fatherhood remains a key element in the discussion of masculinity, and there seems to be broad support for encouraging fathers to be more engaged in child-rearing than they were in the past.
As evidence, Christopher Brown, president of the National Fatherhood Initiative, notes that the military is investing more energy these days in supporting soldiers' roles as parents.
"Fathers are really embracing that broader role," said Brown. "It's become accepted that they can share more of the work and more of the joy."
O'Neil, the UConn professor, would like to see an expansion of psychological support for men wrestling with changing expectations.
"There's denial about men having problems related to gender roles," he said. "We need to break through that."
Gays as well as heterosexuals have played a role in the changing concepts of masculinity. Certainly, Michael Sam - the all-American defensive end who last week told the rest of the country what his University of Missouri coaches and teammates already knew, that he was gay - is already helping break down stereotypes about gay men..
"When it comes to gay men, the script is being rewritten," said Sarah Kate Ellis, president of GLAAD, a leading lesbian, gay, bisexual and transgender advocacy organization. "It's a wonderful thing happening as the definition of manhood evolves and it becomes more inclusive of more types of men."