It may seem inappropriate to describe a women of 5ft 5ins as a giant, but that is the mot juste for world tennis No.1 Justine Henin who announced yesterday that she is quitting her sport with immediate effect.

The decision stunned her sport, and followed just 24 hours after an equally towering figure, Swedish golfer Annika Sorenstam, confirmed that she is to retire at the end of the season.

But there will be no valedictory tour from Belgian Hardin, who in her departure at the very pinnacle of the game has elected to ignore the seductive siren voice which lures so many great sports champions to remain in action well beyond their sell-by date. For all but seven weeks of the past 18 months she has been World No.1.

Both could undoubtedly have racked up more titles and amassed even greater fame and fortune.

Hardin has blossomed from child prodigy to win some $20m in career prize money and earn many times that in endorsements. Sorenstam's $22m career winnings is $8m ahead of golf's next greatest female earner, with an unrivalled 72 tournament wins, 10 majors, and LPGA Tour player of the year a record eight times.

But for both, the hunger and drive has gone. There is a limit to how long one can endure a life defined by long haul flights and hotel rooms, even cosseted in first class and five star. And they have reached it.

Perhaps most of all, they can hear the bodyclock ticking. Henin is 25, with apparently plenty time to start a family, which she has expressed the desire to do. She follows her compatriot, another former world No.1, Kim Clijsters, who retired at 23 and has since married and become a mother. At 37, Sorenstam, who is engaged, has less time, though she has indicated in the past that children are on her agenda.

Both are fortunate to be leaving on their own terms. Injury decides the moment for many of their peers, and increases the trauma. Neither will leave with a sense of unfinished business. Henin missed several months of the circuit in both 2004 and 2005 with a debilitating virus and a catalogue of knee and back injuries. Last year, as her four-year marriage ended in divorce, she won two grand slam titles, while Sorenstam has battled back from a year blighted by back and neck injuries (and a first year without a tour win) to take three tournaments this year.

Henin is the first woman to quit tennis as No.1, but her delivery yesterday eloquently denied any hint of burn-out. Her composure contrasted with her coach, Carlos Rod-riguez, who wept: "Because of her, I am somebody."

Henin seemed unable to recover from two devastating defeats:6-4, 6-0 to Sharapova at the Australian Open, and 6-2, 6-0 to Serena Williams in April.

At last week's German Open, she went down 5-7, 6-3, 6-1 to Dinara Safina. "At the end of the match in Berlin . . . I decided to stop fooling myself and accept it," she said.

But Rodriguez said it was reconciliation with her estranged family that sparked the decision: "Tennis became more than just winning for Justine, and just winning was not enough for her anymore."

In addition to four French Open titles, she also won the Australian Open in 2004, and the US Open in 2003 and '07. The only grand slam title to elude her was Wimbledon. "Winning Wimbledon would not make me happier than I am," she said. "I could never dream of Wimbledon. It was destiny. I didn't feel myself capable. It was too much for me.

"I won Roland Garros four times - three times in a row. I don't have to live that moment again. I know how it was."

Rodriguez coined a fine exit line: "She never craved fame and money. All she wanted to do was play and win."