Serena's battle questions the supremacy of brute strength

A photo-shoot article in last month's issue of Tennis magazine offered potentially depressing viewing for the average operator on the women's tour.

In the text, Kerrie Brooks, physical therapist to Venus and Serena Williams expounds the routines with which, over the last two years, he has strengthened the core muscles of his champion charges. "This has increased their power and improved their stability when they hit," Brooks wrote.

The sisters are pictured in a variety of stressful activities – "Medicine-ball toss on physioball", "Quadruped on foam rolls", "Walking lunges with weights bar" – exhibiting a level of smiling ease that just might cause lesser mortals on the circuit to want to spit.

Now that both these players bestride not only physioballs, but the world game, alongside the hardly less physically imposing figure of Jennifer Capriati, it is becoming accepted wisdom that superior physical attributes are the key to success.

As she prepared to commentate on Venus Williams' second-round victory earlier this week, the former Wimbledon champion, Chris Evert, reflected wryly upon the changing nature of women's tennis. "In our day, Martina Navratilova was regarded as a big player and she was only 5ft 8in," Evert recalled. "At 6ft 1in, Venus Williams makes her look petite. I was glad I played in my era."

Exponents of the argument that power brings glory point to the relative demise of the relatively small – 5ft 7in, 9st 4lb – the former world No 1 Martina Hingis, who has not won a Grand Slam title for two years.

Not surprisingly, Hingis refuses to countenance the idea that her chances of winning against taller, stronger players are now slight. "I don't think it's quite as clear-cut as that," she said. "I've played plenty of matches against the Williams sisters. I even beat them in successive rounds at the Australian Open last year. Nor do I need to change my game altogether to win another Grand Slam title. I proved that in Melbourne. So I won't have to turn into a bodybuilder covered in bulging muscles. There is still more finesse and elegance than sheer power in my game."

Hingis' attitude is replicated by Belgium's 2001 Wimbledon finalist Justine Henin, who, at 5ft 5in and 9st looks like a little girl when matched against some of the tour's larger operators such as Venus Williams or the 6ft 2in Lindsay Davenport.

"There are a lot of well-trained players nowadays," Henin said, "but ultimately the big difference is how you react psychologically to a big match in a big tournament. And that's where I have the edge over many players on the circuit. I don't even think about the size difference being a problem."

Hingis and Henin, of course, would hardly espouse the opposite argument. But on a day when the Capriati swept imperiously through to the fourth round with a 6-2, 6-4 win over Daja Bedanova, of the Czech Republic, there was further evidence here of the validity of their position as Serena Williams, seeded second behind her sister in a season where she has already secured the French Open, struggled mightily to withstand the challenge of Henin's fellow Belgian, Els Callens.

At 31 and ranked 119th in the world, Callens had never been further than the third round in any Grand Slam before this tournament in 11 years of trying. But she very nearly made it yesterday on Court No 2, which has already seen the early demise of Pete Sampras and Kim Clijsters.

On court, Serena presents a very different sight to her elder sister – she has the physical build of a world-class sprinter. And after making a muted start during which she was clearly troubled by losing her footing on a number of occasions, she began to show the power which even Venus was unable to counter in Paris this year.

At 2-2, she went to 30-15 on Callens' serve after contributing five ferocious shots to a rally, concluding with a double-handed backhand that blasted away for a winner. You could see the intensity. You could hear it too, as the American switched her grunt up to maximum volume upon each impact.

But the next point, won by a delicately dinked backhand from the Belgian, stalled Serena's acceleration almost as quickly as it had occurred, and Callens went on to secure the game with an ace before breaking to go 5-3 up.

However, Callens was unable to capitalise on her position, being broken straight back and then succumbing 7-5 in the first-set tie break.

At 4-2 up in the second, the Belgian had another chance to pull away, but once again faltered at the crucial moments and eventually lost the second tie-break 7-2 to a Williams ace.

"It was definitely a little close," Serena said. "Callens played pretty much out of her mind today."

Callens, however, was playing very much within her mind with a calculated strategy of countering Williams' power by playing sliced shots low to her feet. "I saw that she had troubles with it," she said.

As if to add further evidence for the defence of guile against power, the amply biceped Mary Pierce was beaten 3-6, 6-4, 6-1 by Laura Granville. Pierce, a former winner at the French Open, ranked third in the world in the mid 90s, has slipped down to 74th in recent years, but she would have expected to beat the American, who is currently 60 places below her. The jury is still out on the power and glory case.