Thirty-three weeks pregnant with twins, yet determined to lead her talented University of Maryland women's basketball team into the national championships, coach Brenda Frese – known for energetically pacing the sideline – found a novel way to relieve her aching lower back during a home game this month: She had an office chair rolled onto the gym floor.

The result, amplified by a giant color photo in USA Today of a seated, beach-ball-bellied Ms. Frese thrusting her fist into the air, was a powerful visual metaphor for women in the world of sports.

Frese's example, like Paula Radcliffe training through pregnancy and winning the 2007 New York City Marathon, doesn't camouflage – but actually flaunts – the fact that women are physically different than men.

It also challenges an assumption that still dogs women today: The female body is athletically inferior to a male body.

For all the progress women have made – in government, business, and the military – the shadow of female frailty still shapes the environment of sports.

To study the structure of organized athletics today – from youth leagues to the Olympics – is to see a system that feeds the faulty belief that females can't play as long, as well, or as hard as males.

The strict gender segregation of almost all sports is considered normal, even progressive. But separate, it turns out, is not equal.

No, this is not just about athletics. It's about how we view and value one another. That's why it's critical that we create a sports culture that is truly co-ed.

Historical prejudice

To be sure, this effort runs counter to centuries of prejudice. Credit Aristotle for locating female inferiority precisely in the body part men lack: the uterus.

The Victorians perfected this argument, as a cadre of 19th-century physicians and craniologists laid down the "science" explaining the female's natural weakness. Of course, it was rooted in the reproductive role and occasioned all manner of "protections," restrictions, and rest.

Ads for Nike and Gatorade may feature well-muscled, sweat-drenched women athletes pushing personal boundaries, but institutional boundaries remain rigid.

Consider:

•Men's pro tennis players play five sets. Women play three (a holdover from 1902, when the US Lawn Tennis Association cut women's play, fearing over-exertion).

•A 12-year-old girl who enters a local tournament sanctioned by US Kids Golf plays just nine holes; a boy her age in the same tournament plays 18 – regardless of their relative skill or experience.

•Co-ed adult sports leagues are rife with special "gender rules" to accommodate the supposedly weaker female sex. In some basketball leagues, women get two points for every basket; the men get just one. In touch football, a female touchdown is worth seven points; a male TD earns six. A 24-year-old who plays on a co-ed softball team recently shared with us her annoyance at rules (no more than two men bat in a row, men hit larger balls, etc…) which presume that any male player is better than every female player. Her beef? She played Division I college softball.

Of course, there are physical differences between men as a group and women as a group. That would support different rules for super-physical sports such as boxing and tackle football. But how does that account for the disparities in billiards and bridge?! Indeed, given that females are physiologically suited for ultra-endurance events, why are women's Olympic events slightly shorter than men's?

The answer to all these questions, in some form, is that sport is not merely about the game. It is, rather, about the identities of those who play and watch the game. It's about what gets established and reinforced every time sex-segregated formulas cast males as categorically superior to females.

Sports matter – and probably far more than they should. Many more people tune into the Super Bowl than the president's State of the Union address.

When we invest in sports as fans, parents, and recreational players, whether we know it or not, we become complicit in a deeply gendered institution in which male superiority and female inferiority are played out as clearly as HDTV.

Ironically, though, we've come to accept this differential treatment of males and females as "normal." It appears to be all right to charge $4 to see the Rutgers women's soccer team play and $7 to see the men's team play, for example.

Likewise, it seems that no one complained (or hardly noticed) when a Massachusetts youth soccer league put a warning in a bold-framed box at the top of the online registration page for Spring 2008. Local officials were no doubt trying to be helpful – but also reflecting a norm played out in communities across the country. It read, "Note: If you are attempting to register a daughter, please be aware that Newton Youth Soccer is co-ed, but primarily boys."

Replace gender descriptors with words reflecting race or religion, and the problem becomes appalling. Be aware that Jews are welcome, but the league is mostly gentiles? Be aware that blacks are allowed, but the program is primarily white? No way.

Sports are a path to social, economic, and political success. It is not enough to permit girls to play with boys; girls playing equally with boys should be the model. Individual ability – not gender – should be the first line drawn when organizing play, especially when sex-based athletic differences are trivial.

Title IX did open doors to girls and women to play sports on a broad scale. But it never demanded equality. Passed at a time when few could imagine the impressive, talented female athletes we have today, the law has codified a sex-separate athletic system in which men's sports are at the center and women's at the periphery. It's an insult in a non-revenue setting to charge unequal ticket prices. And for marquee sports such as college men's and women's basketball, there should be equal promotion at those institutions receiving federal funds.

Some argue that because the men "play above the rim" it's a more exciting game. Ridiculous. "Exciting" is about talent in the face of talent: competition. The Women's Final Four in recent years has been every bit as nail-biting as the men's NCAA playoff. Differences in style of play certainly don't keep fans from tuning into college football just because of the NFL.

Men and women, playing together

Some worry that having males and females take the field or court together would be a disaster for women's sports. It may be true that the top male players in the most competitive athletic events outperform the top female players. But look at the larger pool and you see vast overlap in the athletic performance of males and females.

Plus, "having game" is not just about raw speed or strength. If that were the case, NFL scouts who clock college players in the 40-yard dash and note how much they bench press would have a simple job on draft day. They don't.

Because females have historically faced athletic disadvantages, they should be able to play on all-female teams if they choose. But they shouldn't be barred from playing on traditionally male teams.

It's in our collective interest to create a playing structure that encourages men and women – at whatever level they can compete – to pass the ball to one another. Professional golf shows us multiple ways to create compelling competition. Stroke play, match play, partner play, skins. Why not pair Tiger Woods and Annika Sorenstam against Phil Mickelson and Lauren Ochoa? Who wouldn't watch?

The road to coed play – like the road to the Final Four – goes through many venues. Let's recognize that creating such opportunities is not only possible, but critical. Because sports – however much we may wish it were just play – carries wider social and political implications. So credit Maryland coach Brenda Frese for showing off her reproductive power and her coaching power in a single, provocative vision.

And know that one who dared register for that "primarily boys" soccer league (and try out for Little League) is a 9-year-old girl who intuitively "gets" the athletic power axis. She wears her hair short, wears boy's clothes, and will only play on teams with boys. Her mom told us why: "She wants to be taken seriously."

• Laura Pappano and Eileen McDonagh are coauthors of "Playing with the Boys: Why Separate is Not Equal in Sports."