THE SURPRISE decision by Ash Barty, Australia’s three-time grand-slam winner, to retire from tennis at the age of 25 has provoked much consternation. One commentator even suggested it was indicative of a different attitude towards the work-life balance among millennials. But Ms Barty is far from the first tennis player to quit the sport in her prime.

Bjorn Borg was one of the sport’s greats, winning five consecutive Wimbledon titles and six French championships. Born in 1956, he was very much a “baby boomer”. But he quit tennis at the age of 26 in 1983, having lost the desire to keep playing (he made a short and unsuccessful comeback in the early 1990s). Martina Hingis, a Swiss player with five grand-slam titles, initially retired from the singles tour at just 22 in 2003.

Perhaps Ms Barty’s retirement came as such a shock because the recent trend has been for tennis players to keep going. The big three in the men’s game—Roger Federer, Rafael Nadal and Novak Djokovic—are 40, 35 and 34 respectively, while Sir Andy Murray is attempting a comeback at 34. On the women’s side, 40-year-old Serena Williams has yet to announce her retirement, although she hasn’t played since last year’s Wimbledon.

Clearly the competitive urge in some athletes is so strong that they choose to play even when they have earned millions and won every conceivable honour. As for the big three, their rivalry may be keeping them going. After winning the Australian Open in January, Mr Nadal has 21 grand slam titles while Mr Federer and Mr Djokovic have 20 each. To finish ahead of the other two might be the crowning achievement for any of them.

But it is easy to imagine that, for other mortals, success may be almost as great a spur to retire as failure. A couple of tennis grand slams brings financial security for life, plus the scope to keep busy as a media commentator. Tennis involves endless hours of practice and fitness training, as well as ceaseless travel round the globe. Often, a successful tennis player will have started the sport at a very young age and will have had little time to do anything else. Ms Barty had achieved her dream of winning both Wimbledon and her own country’s tournament, the Australian Open; perhaps she had no further goal to drive her forward?

The most likely reason for retirement in many sports is injury. Sandy Koufax, an outstanding baseball pitcher, retired in 1966 at the relatively young age of 30, having just won his third Cy Young award for best pitcher. He gave up in the face of crippling arthritis which had dogged him for the previous two years. “I don’t regret for one minute the 12 years I’ve spent in baseball,” he said, “but I could regret one season too many.” More recently, Andrew Luck, the quarterback of the Indianapolis Colts, retired at 29 after a long series of injuries that included a torn shoulder, a lacerated kidney and a nagging ankle problem.

Physical-contact sports like American football or rugby result in a vast range of injuries. But a non-contact sport like tennis still makes enormous demands of the body. Sir Andy now has a metal hip; Mr Nadal has suffered a long series of injuries, in particular to his left foot; Mr Federer has had back problems and, in recent years, has needed operations on his knees. The scrambling, stretching and chasing involved in tennis puts a lot of strain on the joints. Indeed, the sport has a particular injury (tennis elbow) named after it. The real surprise is not that some stars retire early; it is that they keep going so long. ■