The fifth set problem is usually a first set problem

Players who fade late are rarely underconditioned; they have normally spent an unnecessary amount early on points they had already won.

When a player fades in the fourth hour the diagnosis is automatic. Not fit enough. Sometimes true. More often what happened is that they spent the first two sets playing every point at maximum, including a large number of points that were already decided, and the bill arrived later.

Energy in a long match is not spent evenly and the biggest leaks are invisible. The extra sprint to retrieve a ball that was going out. The full swing on a put away that needed sixty per cent. The refusal to let a bad game go, and the resulting three minutes of intensity spent on a service game already lost. None of that shows up in the rally count and all of it comes out of the same account.

Compare this with the players who last. They tend to look faintly disengaged at times, which commentators occasionally read as a lack of desire. Watch closer and you notice a pattern. They concede points cheaply when the point is gone. They take the free ball with a short swing. They walk between points at a speed that has nothing to do with the score. That is not indifference, it is budgeting, and it is a skill nobody applauds.

The conditioning point that follows is slightly awkward for the fitness industry. Above some reasonable threshold, more endurance training does less for late match performance than better in match decisions about effort. You cannot out train a player who is throwing away energy on unwinnable balls, and adding capacity to a leaky system mostly means the leak gets bigger.

The place I would look first is the twenty seconds between points, which is genuinely trainable and almost never trained. Heart rate recovery in that window varies enormously between players and it responds well to breathing work and to simple ritual. Over three hundred points a match, a small difference there dwarfs anything you get from an extra interval session.

There is also a psychological version. Players who cannot let a lost point go are paying for it twice.

The fresh player at four hours is not the one who trained hardest.

They are the one who was cheap when it did not matter.