Sachin Tendulkar's instant angry reaction to being bowled by Tim Southee in the second innings in Bangalore was revealing. His raising of his bat as if to strike out at something appeared to be a show of anger at committing one more mistake: missing another straight delivery. Not only has he never before committed mistakes one after another to such an extent, he has also never shown such emotion upon dismissal. It was indeed a striking moment.

For the first time we may well have seen his nerve show signs of twitching. What has been his greatest strength for well over two decades - his mental toughness and calm under pressure - has finally been exposed ever so slightly, leaving him questioning something deep within.

However, it's only the first sign and means his nerve, theoretically, should hold up for a lot longer yet. The problem is, like with many fine players before him, once it starts, it can all come crashing down in a hurry if awareness is not first embraced. As Sanjay Manjreker rightly pointed out, Tendulkar should work his way out of this hole he is in. That's on the mental level, but what about on the physical level?

Let me explain this hole I refer to. As we all know, Tendulkar is in his 40th year, having endured 23 years of constant grind, scoring the ultimate achievement: 100 international centuries. It's remarkable, really, that he has even lasted this long, just as it was that Richard Hadlee did amazing things in his 40th year too.

That Tendulkar has lasted is due to his astonishing, insatiable love for the game. The hunger to continue to score runs for India, the desire to train just as hard as he used to, the mental toughness to put the unprecedented expectations aside - they are all phenomenal attributes.

His other incredible attribute is his eyesight. For those who might say it is failing him, I will challenge that right here and now with a bit of personal scientific fact. Last year when I visited my optometrist to get proper reading glasses, I expressed disappointment that my eyes were failing. He disagreed and asked me if I would undergo the exact same hand-eye reaction test he put me through 20 years ago in Christchurch. I agreed and five minutes later he pulled out the result sheet from 1992 and compared it to the one from the 2011 test. Staggeringly to me, the results clearly showed that I was 25% faster in 2011, at age 49, than I was at 30. Simply put, the eyes had got better, despite my need to have a lens to see the page a foot in front of me.

Hand-eye reaction is not Tendulkar's problem; he probably is better and faster with his hands than he was in 1992. But the one thing that he can't escape from is that the body is naturally slowing down. Firstly, the back and hamstrings are probably 10% less flexible, and his agility and speed down about that much too. Therefore, while the eyes see the ball and the instinctive mind makes the right decision upon seeing it, Tendulkar will naturally find that he is not as quick as before. In particular, it is against fast bowling that his feet and body will find it increasingly hard to move quickly enough into position.

Turning back the clock physically will call for a major sacrifice, one that would need total dedication to get there and then maintain it. Question is, will Tendulkar be prepared to do that at this late stage of his career?

Against spin he is absolutely fine and as good as anyone in the world. But despite batting brilliantly against Australia's fast men at the start of the year, a pattern began to emerge in his dismissals: playing on, lbw, clean-bowled. Now, nine months on, every team's analyst will tell every fast-bowling attack that, as New Zealand showed in recent weeks, anything over 135kph pitched up full and his feet and body won't respond quickly or for long enough anymore.

Since Melbourne, where he batted like a dream, like a 29-year-old Tendulkar, it feels now as if the secret is out, and the angry moment from him in Bangalore was a small indicator that he instinctively knows something isn't right. With that moment revealed, everyone bowling to him from here on now knows.

Technically his back foot, and in particular his right heel, is planted in the ground. It is not moving with his front foot; it is arriving too late. His front foot moves and hovers forward as the ball is released, therefore both his feet point to the off side, not straight to the ball, and then inadvertently he starts playing around his front foot and either misses it or gets lbw.

But he can fix it. He can get up onto his toes more and he can start to move his back foot fractionally up and down to get it activated. This will help him to start to move both feet when the ball is closing in.

There is, though, no getting away from the probability that his days of playing fast bowling successfully for any decent length of time are coming to a close. Unless he finds some extra agility and speed, his feet and body will simply not get quicker, or be quick enough. Turning back the clock physically will call for a major sacrifice, one that would need total dedication to get there and then maintain it. Question is, will he be prepared do that at this late stage of his career?

He isn't a chaser of records, so that can't be a reason to stay on. He isn't the captain, with his team in dire straits, needing him, so that can't be a reason to stay on. He doesn't need anything, really, as he simply has it all, so that can't be it either. So what is it that will keep him going?

Only deep down will Tendulkar know, and playing South Africa next year, the No. 1 Test team, with the best fast attack in the world, will not make whatever that reason is any easier to deal with.

The god, I sadly suspect, is in the twilight of his career. But maybe Manjrekar is right and Tendulkar will be fine. Maybe, it just takes him a little bit more time to hit his stride these days. And if Tendulkar needs a bit more time to get the body striding forward again, we all have the time to wait and watch in awe, even if it's only for one more magic century moment.

How some of the greats fared in Tests after the age of 35*
Batsman Innings Runs Average 100s/ 50s Career ave
Don Bradman 23 1903 105.72 8/ 5 99.94
Sachin Tendulkar 76 3751 54.36 12/ 16 55.08
Steve Waugh 56 2554 53.21 10/ 8 51.06
Brian Lara 45 2296 51.02 9/ 5 52.88
Graham Gooch 96 4563 48.54 12/ 21 42.58
Sunil Gavaskar 40 1728 45.47 4/ 9 51.12
Rahul Dravid 85 3493 45.36 12/ 13 52.31
Viv Richards 53 2107 43.00 4/ 17 50.23
Allan Border 66 2473 42.64 4/ 15 50.56
Ricky Ponting 48 1865 40.54 3/ 13 52.75
Javed Miandad 19 578 32.11 0/ 4 52.57
* Includes all matches that started after the player turned 35

Martin Crowe, one of the leading batsmen of the late '80s, played 77 Tests for New Zealand