You could have been forgiven for thinking batting was easy.

As Joe Root, for the second Test in succession, passed 150, you might have thought that he was batting without pressure, in conditions where bowlers were unable to gain any movement or purchase. So comfortable did he seem, so serene was his progress, that it would have been easy to underestimate the size of his achievements.

It's only in contrast with his team-mates that it becomes apparent how good a batsman Root is. Having scored 54 percent of England's first-innings runs in the first Test, he has so far scored 55 percent of them in the second. He has scored 305 - yes, 305 - more runs than any other England player in the series.

England have had other batsmen of recent vintage who have scored heavily in Asia, of course. With Alastair Cook, you could feel the struggle: the dogged determination to survive and limited number of scoring shots made every innings something of a battle. With Kevin Pietersen, the talent was so extravagantly obvious - remember those slog-sweeps in Mumbai and Colombo? - that you knew you were in the presence of genius.

It's not like that with Root. For much of the time, his batting is so unobtrusive it can lure you into thinking what he is doing is straightforward.

Think of the way he plays back to the spinners, for example. You won't see many of those singles or dot balls on highlights packages. But they allow him to rotate the strike, release pressure and mess with the bowlers' lengths.

More eye-catching are his sweeps. So broad is Root's repertoire of sweep that he can hit the ball in front or behind square on both sides of the wicket. As a result, he is desperately tough to contain. Even on the second evening of this game, coming to the crease with England 5 for 2, he scored so freely that he reached stumps unbeaten on 67 off 77 balls. Individually those strokes may look routine; collectively, they amount to a masterclass.

But maybe it was fitting, during the innings in which he passed Pietersen's Test run tally, that he also produced several switch-hits to remind us that, underneath the determination to play the percentages, there lurks an extravagantly talented player. To pick the length, to switch his hands, to time the ball to perfection: Root effectively hit more boundaries left-handed than Dom Sibley, Zak Crawley and Dan Lawrence managed between them.

Root also went past the run tallies of David Gower and Sir Geoffrey Boycott - both greats of English cricket - in this innings. There is every chance that, by the end of the year, only Cook will remain ahead of him in terms of England players. For a 30-year-old, these are extraordinary heights to have scaled.

Pietersen once said that of the trio of incredible Test centuries he hit in 2012 (Colombo, Mumbai and Leeds), he rated the one in Sri Lanka the best because the heat and humidity was so demanding. It's not just hard to concentrate in such heat, it can be hard to see with sweat in your eyes, and to grip the bat with damp gloves.

As Root's innings progressed into its ninth hour, the physical demands started to show. He was past 170 before, with body starting to creak where it had earlier eased into position, he gave a chance. And perhaps, a less stiff body might have regained its ground when he hit the ball at short leg only to see the fielder, Oshada Fernando, pull off an almost miraculous stop and throw down the stumps. Root, who had been given a banana and a sugary drink every 45 minutes since lunch - that's seven of each - was just 14 runs short of becoming the first England player to register double-centuries in consecutive Tests since Wally Hammond in 1933. Hammond did it in 1928, too.

Such weariness was understandable, though. Root has, to this point, spent all but 39.1 overs of this series on the pitch. In this heat and humidity, that is a remarkable reflection of his determination as much as it is his dominance. It's telling, too, that of his three dismissals in this series, two have come from run-outs and one came when he was left with the last man in the first innings of the first Test and perished to a boundary catch as he tried to thrash a few quick runs. A lesser player might have had an eye on the not out.

So, what is Root doing differently? Well, from a technical point of view, the obvious change is that he is currently going back and across as part of his trigger movement. In recent months, he had slipped into the habit of merely going back and, as a result, his balance wasn't as good. He also opened his stance, extravagantly at times, to allow him to manoeuvre the turning ball square of the wicket.

But how much of this splurge of runs is down to technique and how much is temperament is hard to say. He went through 2020 without a Test century - the first time in his career he has been through a full calendar year without scoring one - and dropped out of the top 10 in the rankings as a result. That will have hurt.

He admitted, after the first Test, that he spent the weeks from the end of the English season until this tour, thinking about his batting as much as working on his technique. Not just which shots to play, but on the importance of being ruthless and turning more of those fifties into hundreds. At present, he seems able to compartmentalise his batting from the captaincy. This version of Root appears to have the hunger to complement his talent and to understand his side's need for him to contribute far more heavily.

There are, no doubt, tougher challenges to come in the next few weeks. It's not that India necessarily have a better left-arm spinner than Lasith Embuldeniya, or that their pitches will necessarily turn as much. But India do have better seamers and a better offspinner. And they do have much better batsmen. There will, as a result, be fewer release deliveries, and Root and co. will find themselves in the field a good deal longer than they have here. Indeed, the last time they visited Chennai, they were in the field for 190 overs. Even then, India had to declare to end the torture. The burden on Root - with the bat and in the field - will be immense.

You just had to witness the struggle at the other end from Root in this series to know that. England's openers, for example, have now contributed 28 runs between them in six innings. While Root has gone back on his stumps, they have groped forward as if searching for their way in the fog. In this innings, only one other man in the top seven reached 30. There have been times on this tour when it seems some of his team-mates have never seen bowling like this.

Of course, they haven't, really. Crawley has never faced a spinner with the new ball in the county game; Sibley has done so just three times. It will never have been on a surface like Galle, where some balls turn and bounce and others skid on. Ultimately, until the ECB put in place a domestic structure that encourages the development of spin bowling as part of the County Championship programme, it will remain desperately tough for England to challenge in Asia. And yes, that includes not penalising counties who produce turning wickets. If you dedicate the prime weeks of summer to a white-ball competition, you are compromising your red-ball development.

Root, at least, provided an example of how such conditions can be overcome. He is carrying this team, making light of the conditions, the absences and the match situation. It's nowhere near as easy as he has made it look.

George Dobell is a senior correspondent at ESPNcricinfo