Kim Clijsters

Forget Couch to 5K, maybe it should be Delivery Room to Marathon. While many postpartum mamas complain of the toll their pregnancies took on their bodies, doctors claim that the experience may make them more powerful than they were before conceiving a child. Researchers from Michigan State University and John Moores University in Liverpool have found that increases in blood volume and hormones that occur during pregnancy can improve the body's muscle strength, allowing women to excel at athletic activities.

The recent successes of mother-athletes like tennis ace Kim Clijsters, swimmer Dara Torres, distance runner Paula Radcliffe and golfer Catriona Matthew have the researchers looking at the psychological side of birth and athletics. Professor Greg Whyte, from John Moores University, speculates that the birthing process increases women's pain threshold, making female athletes even stronger than before:

"Women re-evaluate where they can anchor pain and many psychologists believe that woman’s pain threshold is effectively reset so that when she resumes or takes up training again, nothing ever seems as uncomfortable."

Did you find yourself stronger after giving birth?

Anger in tennis is not without precedent: Jimmy Connors and John "Superbrat" McEnroe were criticized for their oncourt outbursts at linespeople when they didn't agree on a call; they were also beloved for their passion. But a couple days ago at the US Open when Serena Williams disputed a call by getting in the linesperson's face and allegedly telling her she wanted to shove a tennis ball down her throat, some people didn't think that her punishment was enough.

Williams was fined the on-site maximum $10,000 for unsportsmanlike conduct and $500 for racket abuse, and her action caused her the match point. Kim Clijsters went on to win the match and ultimately the US Open.

Some say Serena's endorsement deals are not in jeopardy, and the crowd booed a reporter who insisted Williams address the issue after winning the US Open doubles match with her sister. But tennis historian Bud Collins was quoted as saying that he couldn't believe that Serena got to play doubles, and that she should be suspended for the rest of the year.

I am shocked that an athlete of Serena's caliber would say something like that in anger, and emotional outbursts or threats make me look askance at the person freaking out. I'm curious though, do you think people are more shocked when they see women get angry than when men flip out?

Just like Paula Radcliffe illustrated that motherhood and winning marathons are not mutually exclusive, and just like Dara Torres proved you can come back after childbirth and win Olympic medals, tennis pro Kim Clijsters shows that you can come back and be a champion as well.

Clijsters retired from tennis in 2007 and gave birth to daughter Jada Ellie at the end of February 2008 after a tennis career winning the US Open in 2005, and making it to the finals in the Australian Open and the French Open. By no means a shabby career. Unranked going into the finals of the US Open, she beat Caroline Wozniacki, ranked ninth, in straight sets 7-5, 6-3. I would say her comeback career is on! Unfortunately, her semifinal match against Serena Williams is probably more memorable than her winning match. To see how much Serena has been fined for her display of unsportsmanlike behavior read more

Serve one up for all of the mothers out there. The decision to return to work after the birth of a baby can be hard. For professional athletes, the preparation requires more than just emotional strength but physical preparation.

Once ranked the number-one tennis player in the world, Kim Clijsters retired from the sport in May 2007 with the intent to marry her boyfriend and start a family. In February 2008, she gave birth to daughter Jada Ellie before announcing her intention to return to the tennis the following year.

This afternoon, Clijsters topped Li Na to move on to the U.S. Open's semi-final round for the first time since 2005. After Clijsters's recent win over third-ranked Venus Williams, CBS Sports' Mary Jo Fernandez asked the mother, 26, about returning to work with a child in tow.

Check out what the athletic mama had to say:

• On how hard it was to return. I've been working really hard the last 7-8 months, and I'm enjoying it. I think that's really something important for myself as well, as long as I can focus on tennis, but on the outside have fun as well. Tennis is a great sport, but I'm just happy that we can have a family and I can balance both.
• On how she balances work and family. We have help, so that's great, but it's fun. . . . To your daughter, it doesn't matter if you win or lose, she's just happy to see me and that's great.
• On how she prepared to re-enter the game: I have to admit that I only just started watching tennis at the start of this year, because I didn't really have that much time. With the baby running around, I was just happy to sleep when she was sleeping as well.