One often hears, from players and television commentators on down, that women’s tennis has more depth today than ever before. Indeed, the best players are more athletic, and there are more of them. Rather than one, two, or three competitive matches in a Grand Slam event, as we might have seen in the 1980s or 1990s, today’s field often produces four, five, or even six real contests per major.

Yet for all this welcome depth, today’s women’s game badly needs something else: consistency.

Seven different women have won the last eight major titles,largely because of injuries. At the Australian Open this year,the field, though complete through the top 20, is ailing again. Maria Sharapova, now more than a year and a half removed from her only Grand Slam title, is suffering from shoulder trouble that slowed her last season. Kim Clijsters, who missed nine months from 2004 to early 2005, has strained her hip and must take painkillers to compete. Alicia Molik, a quarterfinalist in Sydney last year, is out indefinitely with an inner ear infection that throws off her balance and blurs her vision. And perhaps worst of all, 16-year-old rising star Sesil Karatantcheva was suspended for two years after twice testing positive for an anabolic steroid.

Most pressing, though, is the matter of the Williams sisters. Venus and Serena have been beset by injuries, too, and both are in questionable condition with knee (Serena) and hip (Venus) problems as the Australian Open begins. More detrimental to the women’s game, however, is that their tennis continues to decline, rapidly for the out-of-shape Serena, and gradually for Venus.

After winning nine of 16 Grand Slam titles from 2000 to 2003,the Williams sisters failed to win even one in 2004. Last year they managed two – Serena in Australia and Venus at Wimbledon – both saving match points along the way. Yet 2005 hardly presaged a Williams revival. If anything, it might end up being a last hoorah for two players who should, at ages 25 (Venus) and 24 (Serena), be playing the best tennis of their lives instead of watching their rankings fall outside the top 10.

If not for a surprise title in Australia, 2005 would have been an utter failure for Serena. She posted her worst winning percentage since 1998 (.750), her first full year on tour (.725). In the last two years, she is 11-9 against players inside the top 10, compared to 27-5 from 2002-03, when she won five of eight majors.

Serena also lost to worse opponents in 2005.For example,she hadn’t lost to anyone outside the top 100 since 1995 until she fell in straight sets to no. 127 Tian Tian Sun in Beijing in her final match of 2005. At Wimbledon, she lost to no. 85 Jill Craybas for the sole reason that Craybas,a consistent player who lacks power, was in shape and Serena was not. She also lost to no. 26 and retired in two other tournaments after falling behind against no. 28 and no. 24.

Venus has not fallen as far, but her last two seasons, even with her win at Wimbledon, are not encouraging. In 2000 and 2001, when she won Wimbledon and the U.S.Open twice each,Venus had a winning percentage above .900. In 2004 and 2005, she finished at .786 and .787, respectively. Her poor performance against top 10 players is startling: Since 2004, she is 6-14 (.300), including 0-9 in 2004. From 1999 to 2003 against top players, she was 66-25 (.725). And while Venus owns more titles than her sister (33 to 26), she has won fewer of them in the last three years – a total of six – than she did in any single year from 1999 to 2002.

This decline is about more than the fate of two players. The Williams sisters – especially the incomparably talented Serena – should be leading a fine pack of young competitors, as well as dueling with women who are their equals or nearly so, namely Lindsay Davenport, Justine Henin-Hardenne, Clijsters, Sharapova, and Amelie Mauresmo. Instead, Serena is routinely overweight and sluggish on court, wasting the best serve and some of the most forceful groundstrokes in the women’s game.

As for Venus, her tennis has too many valleys and too few peaks – too many lapses in concentration on her serve and lethargy on rallies. Rather than hangnig back on the baseline, she should be charging the net and taking advantage of her quickness and long wingspan.

If the Williams sisters would just pick up the pace in 2006, and if Serena would show, rather than say, that she still wants to remain a top athlete, the women’s game would receive a much needed jolt. Otherwise, expect another wide open year as Sharapova continues to find her way, Clijsters and Henin-Hardenne try to remain healthy, and old-guard players like Davenport and Mary Pierce – even Martina Hingis and Jelena Dokic – look for one more thrill.