‘With Ovo, it doesn’t get any better. But it lasts longer.’

It’s one of the best Swiss advertising slogans. Ovomaltine won’t turn an average skier into an Olympic champion. But perhaps he’ll manage one more run whilst the others are already sitting in the restaurant, tired. That was the idea.

Not better. But longer.

There is a surprisingly contemporary idea behind these words. After all, suddenly everyone wants to live longer. The longevity industry measures biological clocks, analyses blood tests and sells powders, infusions and capsules. We are told to optimise our sleep, ‘hack’ our metabolism and slow down the ageing process.

Perhaps we really will succeed in extending our lives. But what exactly is being extended? Life itself? Or merely a frail and painful existence?

We like to talk about life expectancy. We talk far less often about what we expect from this life. What would we still like to be able to do in the years we’ve gained? Climb stairs. Get up from the floor. Carry the shopping. Play with our grandchildren. Go for walks. Travel. Look after ourselves and others.

That sounds modest. But it isn’t. Because all of this requires a body that is not merely there, but actually functional. A body that carries us.

Our life expectancy may increase, whilst our physical abilities decline. We then gain years of life but lose the vigour to live it. We are around for longer, yet find we can make less and less of this existence. Being there, yet not quite there.

This is the blind spot in many promises of rejuvenation. In this view, a person appears like a machine whose operating life is to be extended. Yet a machine merely has to keep running. A person wants to get up, go out, take part, experience things and make a difference. They do not merely want to exist. They want to be able to do things.

The decisive factor in a long life is therefore not merely its duration. It is the duration of our abilities. How long can we walk unaided, carry loads or break our fall if we stumble? How long can we physically hold our own against life’s challenges?

This requires muscle. It does not merely move our joints; it preserves our ability to act. Muscles are the physical prerequisite for turning the span of our lives into a life well lived.

Yet we treat them as if they were merely a bonus for the athletic. As if strength training were all about biceps and six-packs, a beach-ready figure and a more youthful reflection in the mirror. But it is about something far more fundamental: the ability to exist.

Werner Kieser, the pioneer of health-oriented strength training, said: ‘People grow through resistance.’ This applies quite literally to the body. A muscle grows through resistance. And it shrinks without resistance.

The tragic thing about this is not the smaller upper arm. It is the ever-narrowing scope of our lives. First, an activity becomes more strenuous. Then we avoid it. Eventually, we can no longer do it. This is how a person’s world shrinks, long before their life comes to an end.

No supplement can replace a muscle that never experiences resistance. No capsule will carry us up the stairs. No biologically younger blood test result will lift us off the ground. The muscle cannot be persuaded. It demands work.

This sits rather at odds with an age that seeks a more convenient solution to every problem. We want to live longer, but do as little as possible to achieve it. We invest in prolonging life whilst neglecting to strengthen the vitality of those who are alive.

We might therefore do well to think differently about living longer. Not merely: ‘How can we postpone death for as long as possible?’, but: ‘How can we preserve our capacity to function for as long as possible?’.

That would be a more modest, yet more humane, form of longevity. It promises no immortality. Not even that we will become better people. Only that we might retain the strength to lead our own lives for longer.

Ovo supposedly can’t do any better either. But it lasts longer. For a drink, that’s a brilliant advertising slogan.

For a human body, it would be an even better life goal.