So far this week, you have read about how diet can help keep the ageing process at bay. Today, the focus is on the other part of the equation — exercise.
But don't panic: I'm not expecting you to start training for marathons or lifting unfeasibly heavy weights — although there's absolutely no reason why someone in their 70s, or beyond, shouldn't be able to do this with the right training.
For most of us, exercise doesn't have to be quite so intensive. It can be something that fits very easily into our daily lives — and can be utterly transformative.
So, why do I think I'm the best person to be telling you all this?
For most of us, exercise doesn't have to be quite so intensive. It can be something that fits very easily into our daily lives — and can be utterly transformative
Well, I've worked in public health for more than 40 years, doing everything from helping people stop smoking, to developing screening programmes for older people.
I have written books on disease prevention in elderly people, helped develop NHS Choices — the website that informs patients about their health — and I was also the NHS's Chief Knowledge Officer.
I've even written a book called The Antidote To Ageing, which looks at the scientific evidence that shows your age does not have to dictate your physical health.
I'm a real advocate for people making choices about their own health and a true believer that anyone can make genuinely positive differences to the quality and length of their life, with just a few changes to their lifestyle.
And I don't just talk the talk, I walk the walk, too. I'm 75 years old and I can still cycle the three miles to the station every day. Your age, in numbers, cannot be denied — but it should not be a cause for gloom.
It is a cause for celebration and for taking action to cope with what cannot be denied — namely the effects of the ageing process, which don't suddenly strike when you hit 50 or 60, but, in fact, started at around the age of 30.
However, ageing is not the cause of problems in your 70s and beyond unless you allow it to control your health and wellbeing.
You can seize control by reducing your risk of developing disease, becoming fitter, and adopting a positive and optimistic attitude to life, with all its opportunities and problems — even if you already have a long-term condition.
I recently attended the 100th birthday party of a friend. The birthday boy gave a wonderful speech saying, among other things, that a few months earlier, he had flown for the first time to Israel, together with his companion, and fulfilled a long-held ambition to swim in the Dead Sea. And his choice of present? An iPad.
Admittedly, it is exceptional to be so lively at 100, but, if you reach 90 and are relatively free from the effects of disease, you will be able to live on your own, get about by public transport, maybe even still drive a car, and take a lively interest in current affairs.
So, how is it that we all know of 'old' 60-year-olds and sprightly 80-year-olds?
There is, of course, no denying the existence of the ageing process and that there are only two phases in life: growing and developing, and ageing.
The turning point varies from person to person. However, there is a biological rate of decline that, even with the best will in the world, an immaculate diet and daily sessions with a personal trainer, we are powerless to escape.
And that is the best possible rate of decline. The rate at which we lose the strength to climb a steep slope, for instance, is, unfortunately, likely to be even quicker than this.
I call the difference between the best possible rate of decline and a person's actual rate of decline the fitness gap.
It was something I first described in an article in the British Medical Journal in 1982, when my work with older people in Oxford convinced me that, for many of them, their problems were caused or aggravated by inactivity and loss of fitness.
Because the rate at which we lose our fitness is determined not by genes or age, but by social factors such as the decisions we make about our lives and the pressures that influence us.
For example, my first job in the public health service required me to own a car, whereas, until then, I had lived on my bike.
There are two important points about the fitness gap.
The first is that an inability to climb stairs at the age of 80, or to get to the loo in time, could be solely the result of a loss of fitness, not the ageing process.
That's the difference between being young and being older.
When you're young, lack of fitness affects your lifestyle only if you want to play tennis or football, for example — but, later on, it can be the difference between dependence and independence.
The second important point — and the good news — is that the fitness gap can be narrowed at any age.
And you're in luck — over the next few pages, you'll learn how to narrow the gap by improving your fitness.
Take it from me, the results can be absolutely life-changing.
Back in 'the old days', it was common to recommend rest to older people, or those who had been ill or just come out of hospital, but, these days, activity is promoted and even prescribed.
In most hospitals, patients who have experienced a heart attack will have a consultation with an exercise therapist before being discharged.
They will then be expected to turn up to a gym two weeks later to start their rehabilitation on the treadmill.
Even if you develop a long-term condition, such as heart disease or cancer, fitness remains important — in fact, it becomes even more vital.
Back in 'the old days', it was common to recommend rest to older people, or those who had been ill or just come out of hospital, but, these days, activity is promoted and even prescribed
Heart disease is the only long-term condition in which exercise, especially vigorous exercise, carries a risk, so you must check with your doctor before starting a new regimen.
Other conditions cause different problems. For example, if you have had a stroke or developed severe arthritis, movement will be more difficult.
But there are specialist physiotherapists, skilled in helping people with disabilities, who can design an exercise programme to help you recover strength, stamina, suppleness and skill — not just while you attend physiotherapy sessions, but for the rest of your life.
Always check with your GP before making big lifestyle changes or adopting a new fitness routine.
The four keys to staying in shape
From parking further from the shops to exercising with a stretchy band, how to develop stamina, strength, skill and suppleness...
Fitness is not something just for 'young' people; fitness is far more important for people in their 70s and beyond than for people in their 20s.
That's because it can make the difference between being able to dress unaided or not, or being able to reach the loo in time when nature calls urgently.
Geriatricians — specialists in older patients — know that although it is more difficult to regain 'lost' abilities, such as recovering your balance if you stumble, or walking quickly enough to get to the loo in time, in your 80s, it is still possible. You can even do it in your 90s and beyond.
A project in 2014 found that people with a sedentary lifestyle and reduced mobility showed a significant improvement in mobility and independence by participating in a home exercise programme.
If you take action to get fitter every year during your 50s, 60s and 70s, you will reach the age of 80 or 90 in a much better physical and mental condition.
One indicator of fitness is your pulse.
Fitness is not something just for 'young' people; fitness is far more important for people in their 70s and beyond than for people in their 20s
In theory the lower the pulse, the fitter you are. But as some diseases and drugs can result in a slow heart rate, fitness is best measured by the degree to which the body is 'upset' when it is asked to do extra work, such as running upstairs or climbing a hill.
The fitter you are, the better you feel when your body is asked to do something out of the ordinary, and the less your body will have to change to cope with physical and psychological challenges.
Fitness is all about the four Ss: stamina, strength, skill (balance) and suppleness — and a fifth factor, psychology, which we address on the back page.
And don't worry, this doesn't have to dominate your life. All you need to commit to is a very doable ten minutes a day focused principally on strength, suppleness and skill, then three longer sessions every week, walking, cycling or dancing, focused primarily on stamina.
The great thing about this investment of time is not only the long-term benefit but the immediate one, as it also makes you feel good.
Here's what you need to know about the four Ss and the tiny tweaks you can make each day to improve them, to counter the effects of ageing.
Stamina is primarily the result of the way your heart, lungs and muscles work together when walking, cycling — or mowing the lawn.
Having good stamina means you can also meet demands for extra oxygen when, for example, you have to climb stairs.
The easiest way to improve and maintain stamina is to increase the amount you walk and try to find ways of making yourself a little breathless each day, for example, by choosing the stairs instead of the lift.
It's not about doing anything out of the ordinary, it might be about parking further away from the shops, or taking the stairs two at a time.
The aim is to do something every day that means you are breathing more quickly but can still talk, on at least five days a week, and then to supplement this by going swimming or dancing, or playing tennis, bowls or golf — anything that makes you breathless at least once a week.
Traditionally, people have recommended 30 minutes as the required time for walking, and, if you can do it, this is a good duration to do every day on at least five days a week. But don't let perfection be the enemy of getting at least some exercise done.
Lack of time, however, should not be an excuse to avoid exercise because even if you are working flat out you can still redesign your day to fit in more walking, by