Gael Monfils has pulled out of Metz, with compatriot Nicolas Mahut getting in as a lucky loser.

“During Davis Cup, I hurt my abdominal on a serve,” said Monfils. “I saw the doctor and have to rest a bit.”

Richard Gasquet defeated Paul-Henri Mathieu 4-6, 7-6 (5), 7-6 in an all-French matchup.

In a cover appearance on Maxim magazine this month, Anna Kournikova says she has become a U.S. citizen.

“I’ve always considered myself half-Russian and half-American. It never seemed to really matter if I had a passport or not,” she said. “But when I started working with the [United Services Organizations] and the troops overseas, it just seemed the logical next step.”

We’ll answer your health, fitness and nutrition questions here each week. Click here to submit one of your own.

I’m looking for shoulder exercises. Can you help me? Thanks.—Jim Filippo

An injury to your shoulder can keep you off the court for months. Take Maria Sharapova: She was sidelined for nine months after having surgery on her rotator cuff in 2008, and she still hasn’t been able to climb back to the top. “The majority of upper body injuries in tennis players are shoulder-related,” says Dr. Mark Kovacs, manager of USTA Sport Science. “So spending time on rotator-cuff strengthening and shoulder flexibility, especially internal rotation of the shoulder, is really important.”

When you exercise your shoulders, you’re actually working the four muscles of the rotator cuff, which stabilize the joint. Resistance band exercises are great for the shoulders because the work you do to control the motion fine-tunes and strengthens those muscles. For more on keeping your shoulders healthy, read this article from TENNIS Magazine, and click here for some sample exercises.

I’m a 55-year-old male who plays four to five times a week. I’m looking for some stretching and strengthening exercises that will help me stay injury-free. The wear and tear on the hard courts is starting to be an issue with my kness, back and shoulder, and I’d also like to address my core. Thanks.—Frank Redman

It’s great that you’re seeking to strengthen and stretch, Frank. Both are essential if you want to prevent injury and stay fit, and adding strength is particularly important as you get older. “Strength training and especially power training as we age has been shown to be really beneficial,” Kovacs says. He recommends you consult a qualified strength and conditioning coach or a physical therapist to start a regimen.

Another option would be to check out a book like Complete Conditioning for Tennis by E. Paul Roetert and Todd S. Ellenbecker, which comes with a workout DVD. It gives you exercises and tips to help you gain flexibility and strength and prevent injury throughout the body. For a more bite-sized guide, check out our rules for keeping fit as you get older.

Also, it might be time to ditch the hard courts. More forgiving surfaces like clay or grass will limit the pounding on your body. And no matter what courts you play on, Kovacs says, watch what you wear on your feet: “Really make sure that the shoes and any inserts or orthotics are replaced regularly and are of high quality.”

What are the best exercises to improve the serve, especially for beginners? Do I need a strong core or shoulder?—Aris Morales

You definitely need a strong core and shoulders. “But for a beginner,” Kovacs says, “probably what will give you the biggest return is developing some lower-body power.” Kovacs recommends you do plyometrics to gain power. That’s “anything that’s explosive and requires the athlete to get off the ground,” Kovacs says. So if you’re new to tennis and want to beef up your serve, get moving with things like jump squats, high knees and figure-8s.

What’s the most important statistic in tennis? The answer may surprise you. (Or it may not. It’s not like it’s "second-serve points hit into net" or anything.)

But before we get to that, a thought about tennis and stats. Over the past few months, I’ve been hearing and reading some laments of tennis fans and writers that the statistical revolution which has hit other sports has yet to make its way to our game. 

Baseball has long been considered the sport best suited to statistical analysis. The head-to-head matchup between pitcher and batter is one of a number of factors that helps provide a bevy of data which can be analyzed to produce mathematically complicted stats that help define a player’s true worth. For decades, baseball fans had to rely on largely arbitrary numbers like RBIs, runs, batting average and wins. Now WAR and OPS+ give better representations of individual talent.

Even football has intelligent stat analysis, despite the fact that the team nature of the game should make it impervious to such things.

Through all this, tennis has been left out. We’re still looking at the same numbers we did 30 years ago. First-serve percentage and break points and serve speed. It’s 2010 but analysis of tennis is stuck in the pre-computer days.

The sport should be perfect for smart, reasoned mathematical research. Its head-to-head format leaves even less room for variables than in baseball, where the speed of a center fielder or range of a shortstop puts some question marks on data. Tennis is one player against another. The ball is either in or its out. In the net or not. Backhands, forehands, overheads, volleys, break points, game points, match points, holding serve, aces, length of rallies, first set vs. third set — I could go on and on. There’s a goldmine of data waiting to be tapped and decoded.

This week, the Harvard Sports Analysis Collective, a student organization dedicated to the analysis of sports strategy, started to do just that. The group posted findings about which tennis stats best predict ATP rankings. They looked at five variables — aces per game, service-hold percentage, return-points-won percentage, break-points-saved percentage and break-points-won percentage — and compared them to rankings points to look for the best correlation. Their findings were marginally surprising.

According to the HSAC, service holds are the best predictor of who will top the rankings. Most of us could have predicted that; win your serve and it’s difficult to lose the match. What was a bit surprising is that the percentage of break points won isn’t the best predictor of rankings success.

It is certainly surprising that player performances in break point situations are insignificant determiners of world ranking. If you were to look at who currently leads the ATP tour early on this season in break point stats, names such as Rafael Nadal, Roger Federer, and Andy Roddick would frequent the list. Break points are considered the "clutch" moments in tennis, and the players that win them often attain insurmountable advantages in matches. One would assume that winning or fighting off break points (representative of break points won % and break points saved %) would result in match wins which would increase ranking points.

If you want to read the mathematical jargon stating why, let the HSAC explain it you. 

The study isn’t perfect, as its authors would be the first to admit. There’s no causation, most of the stats are dependent on the quality of opponent, and percentages don’t always tell the whole story.

For instance, let’s say Player A and Player B both break their opponents’ serves. Player A did so after getting out to a 40-0 lead, but then having to hold on to win in a second deuce. Player B got out to the same 40-0 lead and won on his first break point. Player A’s break-point percentage is 20 percent, Player B’s is 100 percent. The result was the same.

On a similar note, in the U.S. Open final, Novak Djokovic was 3-4 (75 percent) on break points. Rafael Nadal was 6-23 (23 percent). Which would you rather have?

But these are quibbles that can be ironed out down the road by people much smarter than me. I’m just glad there’s a growing dialogue about this. It would benefit fans (who’s clutch, who’s not, does clutch even exist?) and players (which player can’t hit a backhand on break point, is coming to net more effective on a second serve on clay courts?) alike.

The revolution is coming to tennis. Get out your calculators.

Game Point is Busted Racquet’s roundup of facts, figures and links from around the web.

Love – The WTA turns 40 Thursday (but doesn’t look a day over 29). Read about the nine women who signed $1 contracts with the fledgling tour in 1970 and helped turn women’s tennis into the most lucrative professional sport for women. Without Billie Jean King, Rosie Casals, Nancy Richey, Kerry Melville, Peaches Bartkowicz, Kristy Pigeon, Judy Dalton, Valerie Ziegenfuss and Julie Heldman, Serena Williams isn’t getting equal pay to Rafael Nadal at Wimbledon and Maria Sharapova isn’t putting $25 million in the bank each year.

15 — Speaking of 40th birthdays, Kimiko Date Krumm hits the big 4-0 next Tuesday but got the celebration started early with a win over No. 2- seed Anastasia Pavlyuchenkova in Seoul. The victory advanced Date Krumm to the quarterfinals of the Korean Open.

30 – Serena Williams will not play in the Pan Pacific Open. I, for one, am shocked!

40 — Upon his arrival in Bangkok for next week’s Thailand Open, Rafael Nadal was given the royal treatment.

Game — This video of a 12-year-old Rafael Nadal has been making the rounds for the past few days:

Stanislas Wawrinka will play Valencia this fall instead of the ATP event in Basel held the same week.

Headlines in Switzerland described Wawrinka as ’sulking’ and ’turning his back’ on the Swiss tournament, which is headlined by hometown favorite Roger Federer.

Wawrinka, who played and won his local challenger in Lugano just before Wimbledon, also missed the Swiss tournament in Gstaad held shortly after Wimbledon. He has been a consistent presence for Switzerland in Davis Cup, which has had only selective appearances by Federer in recent years.