Racket head speed is borrowed against the fifth set

A lighter, faster frame buys free power for two hours and then quietly hands the bill to a tiring arm.

Frames have been getting easier to swing for thirty years. Stiffer layups, thinner beams in the throat, weight moved towards the head so the same effort produces more speed at the point of contact. All of that is genuine engineering and it works exactly as advertised for about two hours.

Then the arm gets tired, and the design that was helping starts charging interest.

The trade is straightforward once it is stated. A frame with mass concentrated further from the hand has a higher swing weight, which means it plows through the ball and takes the incoming pace without twisting, but it demands more from the shoulder on every stroke. A frame with the mass closer to the hand is quick and forgiving to swing, and a player can generate huge racket head speed with it, but the ball is doing more of the deforming and the player has to supply stability that the frame is not supplying itself.

Fresh, that second player looks devastating. Deep in a long match, when the muscles that hold the wrist firm through contact start to fade, the same racket begins to twist on off-centre hits. Not much. Enough that balls that were landing on the line start landing two feet inside it, and the player who was hitting through the court is suddenly hitting into the middle of it.

Which is why I am wary of the standard advice given to club players and juniors, which is to go lighter as soon as anything hurts. Sometimes correct. Often it treats the symptom and worsens the cause, because a light frame transmits more shock to the elbow on a mishit than a heavy one does, and mishits are what a tired player produces.

The players who last tend to end up on frames heavier than their game would seem to need. That is not tradition or superstition. It is that they have played enough fifth sets to know what their arm feels like at the four hour mark and have chosen equipment for that version of themselves rather than the version who walks on court at the start.

Pick the racket for the hour when you are worst.

Anybody can hit a good ball when they are fresh.