A long-held belief that I am invincible was tripped up last week when I injured my back while tying my shoelaces.
It is a shock to realise that a 35-year-old body is actually very different from one in its 20s.
Two doctors and multiple friends and relatives have told me not to berate myself over the indignity of this injury: lumbar strain sustained while sitting on a stool and putting on trainers before a weekend Zumba class. It is an action I have repeated at least a thousand times in my life and one I would never have considered harmful.
"It happens, it's normal, you'll just have to be more careful from now on," I have been told, along with statistics that show at least three-fourths of the human population suffer similar back problems.
People have been generous with their sympathy and with careless warnings that this setback could be the first of many, that more and more tiny discomforts might accumulate over the years.
Among the most frightening throwaway comments came from my mother, who is the poster child for active ageing.
"You get used to a baseline level of pain," she said.
Prone on a firm mattress last week, I had little to do but stare at the ceiling and think about this - the only way to read was to hold the book perpendicular to my face, a position that could not be sustained for very long.
The temporary reduction in mobility made me sharply aware of my body.
Like many white-collar workers, I experience pleasure cerebrally, through words and art, more often than rejoicing in the remarkable ability of my muscles and bones to move, lift, act and react.
I do exercise for more than 150 minutes a week, not counting beating the streets for news as a books correspondent, but I never before really appreciated the amount of activity my body is capable of.
Bodies are superbly constructed devices and perhaps we would be more aware of our own if they came with manuals just like computers or smartphones do.
There could be sections telling us how long the warranty lasts on each moving part, how to extend the functional life of each part and how to come to terms with regular wear and tear and inevitable decay over the decades.
I raced through my teens and 20s without really noticing the warranty period ticking away.
I worked 36-hour days, climbed stairs and sprinted for buses. I slung a dozen books in a shoulder bag to return at my local library and brought home the same number again.
Now I get cranky if I'm not in bed by 11pm and prefer more frequent trips to the library to exchange three or four novels.
For a short while, as I recuperate, I will swap rushing for trains and buses with gentle walks and think twice before lifting beds to sweep under them, manhandling potted plants or bringing home heavy groceries.
On the plus side, slowing down allows me to revel in small victories, such as climbing a short flight of stairs or being able to wash the dishes after dinner. I am more aware than ever of the flex of my spine, the strength of my arms as I lever myself into and out of seated positions.
I have learnt sympathy for people I never understood before, those who detest their age. I do not yearn for the appearance of youth but I am terrified of losing its functionality.
I watch elderly neighbours on morning or evening walks, carefully covering short distances with the aid of an umbrella or walking stick and review my maternal grandmother's life with new awe and understanding.
A back injury confined her to bed for years before she died. A doctor who had travelled the world with her husband for half her life, scaling the pyramid of Giza, Egypt and the ruins of Pompeii in Italy, she maintained good cheer and a positive outlook even in those years when she could no longer manage a simple car ride to a nearby park.
I have no idea how she kept her spirits up, when three days of enforced immobility left me rabid and ready to rend all sympathisers. But her life gives me something new to aspire to.
If I can no longer think of myself as invincible, I can aim to be indomitable, as she was. That would be a super power worth having for the rest of my life.