Not long ago Shane Watson was a crock. Now he counts among the most valuable cricketers - might even top the list - and serves as vice-captain of his country. It is an astonishing turnaround that speaks of commitment from the player, faith from the selectors, and a reminder of the truths that ability counts for a lot and that both mind and muscle can betray as often as they advance.

Through all the ups and downs, the endless niggles, the unkind laments, Watson has remained intact. For an unconscionable time it seemed he was deluding himself as he shrugged off another untimely injury and said that sooner or later he'd make his mark. Not without reason, he was designated as a gym cricketer, a calendar pin-up, a sportsman of rippling biceps but stuttering movement, an Atlas able to hold up the heaviest of weights yet not able to finish an over without hobbling off the field.

At once he had everything and nothing: he could crack boundaries and send the ball down at 140kph but could not compel his body, apparently his pride and joy, to complete a match. With the cruellest of ironies, his strongest asset, his strength, was also his weakness because it denied him rhythm and reliability - prize possessions in any cricketer.

It is well known that some injury-prone cricketers have chicken hearts, whilst others seek insurance payouts. Everyone knew that Watson was dedicated and desperate, but it was widely accepted, too, that he was not going to make the grade, let alone challenge Jacques Kallis' tenancy of the most-valuable-cricketer position.

Watto was never a laughing stock because his sincerity was manifest. Nor was he a cause for pity - after all he had an awful lot going for him. Rather, he evoked frustration tinged with sympathy. Repeatedly he would return to the field, his eyes full of hope and determination, repeatedly he would limp off again a few hours or days or weeks or even months later to face another gruelling period of rehabilitation. Most likely in the meantime he had whetted the appetites of captains, coaches, selectors and supporters with a few lusty contributions. Always Watson seemed to be hovering on the brink. Actually he hovered on two brinks, calamity and triumph, and looked both in the eye.

In hindsight, and it is the wisest of states, Watson's conduct during these times of trial and tribulation was underestimated. Somehow he held himself together. His bones might break but his spirit remained intact. Each time he returned to the gym and set about repairing the damage. Evidently cricket was not a soft option for him, it was the only option. He could not walk away. He was a cricketer and he was bound to the game till it closed its doors on him. Devotion is best tested by rejection.

Eventually Watson realised that his instinctive response to every setback was the very thing that caused the setback in the first place. His determination to get back into the gym and lift even heavier weights and to make his body even stronger was bringing him down. In trying to make himself indestructible he had merely succeeded in making himself ever more fragile. He wanted to be a man of marble but instead was made of porcelain. Plain and simple, his body was not properly prepared for the demands of the cricket field. Perhaps, too, he had allowed vanity to run a little too freely. It was a time of introspection and accountability. Watson realised that sensible batsmen ditched the shots that brought them down or learned to play them better. Clearly the principle had a wider application. Only a fool keeps asking the same question and expects a different answer.

Seeking a training regime that suited his game and pushed him hard, Watson stopped lifting heavy weights and started concentrating on aerobics, or exercises as they were called in less fashionable days, when people talked not of Reeboks but sandshoes, not of pilates but running and push-ups. In a trice Watson's fitness, and so his fortunes, changed. Sometimes the solution is blindingly obvious. Sometimes it is discovered only by the desperate.

Suddenly Watson started bowling flat out and hitting the ball hard, and he did so without feeling any pain or fearing any jolt. At first the entire cricket community held its breath. He had not told anyone about the change in his regime, and the clues were few and far between because he still looked more like Arnold Schwarzenegger than Twiggy. Just that he kept playing and did not break down.

Eventually Watson realised that his instinctive response to every setback was the very thing that caused the setback in the first place. His determination to get back into the gym and to lift even heavier weights and to make his body even stronger was bringing him down. He wanted to be a man of marble but instead was made of porcelain

And with every passing week his confidence grew. Long in the habit of choosing him whenever his body allowed, the selectors sent him to England for the 2009 Ashes tour. From a distance it seemed that he was going mostly as a back-up, to lend a hand with bat or ball. Later the selectors insisted that he had been picked as the reserve batsman in a squad dependent on six specialists, some of them flighty. Watson had played Shield cricket as a specialist, batting No. 4 for Tasmania in one of his periods of rehabilitation. He had scored a lot of runs too, though that was not unusual in those parts in those days.

Indeed Watson had failed to meet only one of challenges in his path during the somewhat scratchy early years. He had flopped as an opening batsman. If Australia lost an opener to form or injury they were in more trouble than a kulfi in a tandoori. And so the news that Watson had replaced Phil Hughes at the top of the order for the vital Edgbaston Test was greeted with alarm from Australian fans. Had the think tank gone stark raving bonkers? Even taking Hughes' struggles into account the risk seemed reckless.

In the ensuing 18 months - how much longer it seems - Watto has turned his career around (it would be misleading to say he turned his life around because he never allowed it to sink in the first place, never lost momentum, never allowed the world to best him). And his assertion of his true self began in that very first match, with a string of fierce pulls executed without the slightest hesitation, and a succession of clattering drives played with the broadest of bats. And all of it was done without any hint of nervousness or any sense that he did not belong. His method was simple and his bat was straight. After a long period of struggle, he became an overnight sensation.

Yet despite appearances, Watson is not Superman and could not rescue his team from every peril or perform mighty feats after donning the cap. For a time, too, he was held back by the tightness that comes with a Test hundred in sight (one wit wrote that he had a worse time in the 90s than Kurt Cobain). It told of the sense of history that marks the true cricketer. Repeatedly he would drive, cut and pull his way towards three figures only to turn to jelly with the honour in his grasp. Eventually he broke the curse, though it took a dropped sitter at backward point to allow it. In ODIs, too, Watson has tended to lose his wicket after reaching 50, a trait that might be blamed upon his commitments with the ball. Batsmen tend to assume that bowlers are sensitive simpletons until thrown the leather, whereupon they discover the intensity of concentration demanded by the activity.

Despite these minor failings - and they indicate the extent of his success - Watson has become a formidable figure in the game. To put him alongside Kallis as the most valuable of modern cricketers is not to belittle Kallis or to suggest that Watson is his equal as an allrounder. In that regard Kallis' sustained achievements confirm that he belongs in a higher category, though the modern custom of putting him beside Garry Sobers ignores the West Indian's extraordinary range and capacity for changing the course of matches.

By no means can Watson be mentioned in the same breath as these great cricketers. Illogical as it might sound, though, and taking all forms of the game into account, a strong case can be made for regarding Watson as the most valuable player in 2011. After all, he opens the innings for his country to telling effect, scores quickly, takes his catches, and picks up wickets with the ball, especially when conditions favour swing. He is also widely respected and often volunteers to attend press conference after a bad day. Journalists notice these things. In 50-over cricket he hits the ball with immense power and often bowls his 10 overs. He is consistent because his technique is simple and based upon the perpendicular and horizontal. Like most rural Queenslanders he does not bother much with the dainty; he knows it cannot survive a bushfire, a drought, a cane toad or a dodgy deck.

Watson is no less a match-winner in Twenty20, a point he proved once again as Shane Warne bid farewell to the game, managing not to upset any pompous officials along the way. Like so many other attacks, the Mumbai Indians could not survive Watson's carving power. It is said of MS Dhoni that he bats like a caveman. Watson's power is not so much primitive as raw, and his game is built on strong foundations. Nor is it quite accurate to say that he lacks subtlety, for when the mood takes him and the moment requires it, he can glide, deflect and improvise with the best of them; just that it tends to get lost amid the blows.

And Watson has one other priceless quality, the most unexpected of them all. He stays fit. It has been quite the transformation.

Peter Roebuck is a former captain of Somerset and the author, most recently, of In It to Win It