Like moving, for example. Not house, just a muscle. One has reached an age that tying one's shoelaces is an effort. Tying two's shoelaces would be a step too far.
There is a quiet mystery about this pain, but a sharp twinge is also evoked by odd pieces of news from the outside world. The passing of all horseracing from BBC television causes me some hurt and it deserves a eulogy. It should, though, be a celebration rather than a gloomy obituary.
There are reasons to be cheerful. First, the racing will be on Channel 4, so the sport will be covered with a diligence and professionalism on council TV.
Second, the BBC coverage will be remembered with affection and admiration by this observer, who has some cause to recall the odd race with the sort of pain that occurs sharply in the upper thigh, just about where one's money should be.
These days every sport, every event can be found on the telly. The second legs of the Turkish Cup are probably being replayed somewhere at this precise moment.
But in the time of my youth, the racing was on BBC and ITV and only on Saturdays and special occasions. You may be surprised to learn there was no telly in the bookies. You may be more surprised to learn there was telly in my youth.
The racing had to be watched at home, with Dickie Davies introducing the ITV 7 and Peter O'Sullevan calling them home on the Beeb. This caused something of a problem for me. Telly was a late arrival in the MacDonald household. And so was an inside toilet. And pater was not a punter. He was uninterested in all sport but he reserved a special disgust for horseracing, specifically its gambling element.
Now, I started punting when I was so young, my buggy was parked outside the bookies. There was no way I could enter the hallowed interior of the turf accountants. I had to scribble my selections on a piece of paper, ask a grown-up to take it in and attach my nom de plume (Farleys Rusk) in the full flush of hope that makes a fool of every toddler.
I then had to race home and trust that pater had found something to do that did not involve plonking on the telly. Mater was never a problem. She was cooking, feeding and cleaning a home that contained seven people. The telly was in the house for five years before she noticed it was there.
The excitement of watching one's money go down the stank was accentuated by the knowledge that the telly could be turned over at any moment by pater, who could spot the listing of a BBC2 documentary in the paper on the couch from the top of Ben Nevis on a particularly misty day.
But if the telly stayed on the racing, it was O'Sullevan who captured my mind and my heart. He is, blessedly, still with us, aged 94, or it may be 5-2. Sir Peter was the Mill Reef of commentators, with two conspicuous gifts. First, he knew his racing. Second, he was a punter.
The two, of course, are not always conjoined. Peter could describe a race with a keen eye and an even keener appreciation of what it meant to the observer at home. He will be remembered for the ability to pick the precise words in the biggest of races but he was consistently brilliant, knowing that the humblest of contests carried a significance for trainer, owner, jockey and the wee boy in his living room with his tanner patent.
As I grew, I listened to Julian Wilson, watched as Clare Balding stood on no ceremony as Willie Carson stood on a box and admired Jim McGrath, who took over the commentating reins from Sir Peter.
My horses won, my horses lost. And then I stopped betting entirely. But I continue to watch the racing with an interest that stops short of the financial. I have noted that the sport has gradually slipped on to satellite channels over the years and one can sit in the modern bookies and see all the races on giant screens.
This is all, no doubt, to be commended, but I mark the passing of racing from BBC telly with a deep sigh. This may be the result of nostalgia. Or maybe it's just that I am tying my shoelaces.