JUST two months ago spectators at the Cincinnati Masters, one of the world's biggest tennis tournaments outside the grand slams, may have witnessed the most explosive groundstroke ever. On August 20th, battling for a place in the final, Britain's Andy Murray (pictured) pounced on a short ball from Mardy Fish, his opponent, moving inside the baseline to rifle an inside-out forehand past the lanky American. After a slow-motion replay, the camera flashed up a winner speed of 124 miles (200km) per hour.

Whether Mr Murray's shot is the fastest forehand ever recorded is a popular topic on various online forums. It clearly beats the forehand of just under 120mph struck by Gael Monfils at the 2007 Australian Open, widely regarded as the fastest until this year. But players are not only pushing the limits on groundstroke pace. Since the 1990s the amount of topspin generated by the elite players has risen sharply. While Pete Sampras and Andre Agassi would typically produce 1,800 ball revolutions per minute off their forehands, Roger Federer's shots have been measured at 2,500 and Rafael Nadal's average about 3,200. At such a level, topspin becomes an offensive weapon, driving opponents off the court and forcing them into errors. And serve speed is still rising inexorably. Croatia's Ivo Karlovic set a new world record of 156mph in March this year.

The International Tennis Federation, the sport's governing body, is starting to get concerned about just how long the game can continue to evolve this way before it becomes unplayable. While innovations in racket and string technology have previously introduced more power into the game, the players themselves are responsible for the changes happening today. Taller, stronger and fitter than past generations, they have also been exploiting new methods of training. “The danger is that if the game continues to get more dynamic, and players continue to hit the ball harder, then at some point the equilibrium you have between striker and receiver will be lost,” says Stuart Miller, the ITF's head of science and technology. Fans would surely lose interest if the prolonged rally disappeared and the game degenerated into a mind-numbing series of aces.

Few are panicking just yet. Indeed, this equilibrium appears to have been restored to the sport over the past decade. In the late 1990s, the big servers seemed unstoppable and rallies of more than three shots were a rarity. The nadir came in 2001, when Croatia's Goran Ivanisevic, then ranked 125th in the world, served up a record 213 aces on his way to winning Wimbledon, beating Australia's Pat Rafter, another big server, in the final. A year later, in his autobiography Serious, John McEnroe, a 1970s star, proposed making several changes to boost interest in the game. These included moving the service line closer to the net and mandating the use of smaller and less-powerful wooden rackets. The following year a group of former Wimbledon champions including Mr McEnroe, Bjorn Borg and Martina Navratilova penned an open letter to the ITF demanding a reduction in the size of rackets. It was the last major call for changes the governing body has received.

What has happened since then? Many observers suspect tournament organisers have slowed down court surfaces, introducing materials to make the ball lose speed on its bounce. This would certainly have taken the sting out of serves and facilitated longer rallies. The ITF, however, says there is no evidence of systematic and deliberate manipulation of court pace. Its view is that players have simply adapted to the new power play—either by improving their footwork or by reading more advanced cues from a server. Yet Mr McEnroe and his supporters may not be entirely happy. In their 2003 letter, they harked for a return to the style of tennis played in the 1980s. Of greater concern to the ITF is that players can only adapt so much. As Mr Miller puts it, if certain “hard physiological limits” were broken, the receiver would stand no chance. At that point, authorities would need to intervene.

As far as the ITF sees it, wooden rackets are definitely not the answer. For a start, they can generate similar ball pace to carbon-fibre ones if swung quickly enough. In addition, as the ball travels only about four centimetres across the racket face during a modern forehand stroke, there is still enough space on a wooden racket to produce terrific amounts of topspin. Because they do not allow the same margin for error as today's rackets, players might opt for a safer and less powerful approach. But that is far from being a certainty. Even if this happened, the style of play would not necessarily revert to that from 30 years ago.

A more likely intervention would be some fiddling with court pace. That may have happened anyway without the ITF's involvement, but the governing body is beginning to weigh into this area. Nations hosting Davis Cup and Fed Cup matches are not allowed to manipulate court pace outside certain boundaries established by the ITF. That prevents Spain from constructing super-slow clay courts, or the United States from designing lightning-quick hard ones, to suit their own players' preferred styles. The ITF has also developed a larger tennis ball, called the Type 3, which travels more slowly through the air. This did not catch on when introduced in 2002 because the problems it was intended to address, such as nullifying the power of the big servers, were soon being solved in other ways. Yet the option remains available to tournaments under ITF regulations.

Perhaps the biggest worry for the ITF is that technological changes prove pernicious. Authorities can always outlaw something that is obviously disruptive. That happened in 1978, when the ITF banned the unconventional “spaghetti stringing” used the previous year by Romania's Ilie Nastase to double the amount of topspin on his groundstrokes. But new equipment can have unintended and unforeseen consequences. When larger rackets were first developed in the late 1970s, they were meant for amateurs struggling to hit the ball, not professionals craving more freedom of movement. It is only quite recently their effects have become fully evident. “Prediction is probably the hardest thing we have to do,” says Mr Miller. As players themselves start to threaten the game's equilibrium, it may become the most important.