If you want to protect your heart in old age, get in a pool. I have spent 30 years at the University of Texas at Austin studying how the cardiovascular system responds
to exercise, and nothing I have found comes close to swimming for protecting the heart.

The evidence for this has been building for years. A landmark study from the University of South Carolina followed more than 40,000 men, aged 20 to 90, over three decades. Swimmers were 53% less likely to die during that period than men who did no exercise and 50% less likely to die than walkers and runners.

In a study I published in the American Journal of Cardiology, we put a group of adults over 50 through a swimming programme. We found that three months of regular swimming was enough to soften stiff arteries – one of the single most important things you can do to protect the heart as you age, as well as reduce blood pressure. To understand why that matters so much, you have to understand what arteries actually do.

Heart disease is really a disease of the arteries

Most people think of heart disease as a problem with the heart. It is really a problem with the blood vessels.

We tend to picture arteries as pipes, and blockages as the danger – and blockages certainly matter. But arteries do something else that almost no one talks about: they cushion the blood. Each time the heart beats, the arteries expand to absorb the surge; between beats, they spring back, pushing the blood onwards. That buffering is one of their most important jobs.

As we get older, the arteries stiffen and lose that spring. And this is where the damage begins. When the arteries can no longer absorb the surge of each heartbeat, that force is passed straight through to the small, fragile blood vessels inside our organs. The ones that suffer most are those that soak up the most blood when we are at rest: the kidneys, the eyes and, above all, the brain. Year after year, that battering damages them.

A surprising amount of what we write off as normal ageing – failing kidneys, fading eyesight, a declining memory – is really the consequence of arteries that have hardened.

Stiff arteries are hard on the heart itself, too. A stiff, unyielding artery is more difficult to push blood into, so the heart has to work harder with every beat. Worse, the stiffening can throttle the blood supply feeding the heart’s own muscle. This is why keeping the arteries supple matters so much – and why swimming, which does exactly that, is so good for the heart.

Why swimming beats running for the heart

Swimming is one of very few activities that works the entire body at once. Unlike running or cycling, which are mostly driven by the legs, swimming uses the arms, shoulders and core as well – four limbs moving together.

This matters because of the particular way exercise keeps arteries healthy. When you exercise, your heart pumps harder and blood rushes faster through the arteries. That rushing blood pulls at the cells lining the vessel walls, and – this is the key part – that gentle tugging is a signal for the artery to relax, widen and, over time, grow more elastic.

The more of your body you use, the more blood you move, and the stronger that signal becomes. Because swimming works all body parts at once, it moves more blood than almost any other exercise – which is why it is so good at keeping the arteries young.

There is something special about the water itself

Being in water appears to add a benefit over and above the exercise. In one study I ran, I compared ordinary cycling on land with cycling done in water, matched carefully for effort and heart rate. The water cycling produced the greater improvement in heart and blood-vessel health – the water itself was contributing something.

Two things seem to be at work. The first is hydrostatic pressure: water pushes on the body from all sides, helping to drive blood back towards the heart. The second is posture. In the water you are horizontal rather than upright, which makes it easier for blood to reach the brain.

We now know that too little blood flow to the brain is one of the factors behind dementia, so by boosting blood flow to the brain in this low-strain position, swimming may help protect it in a way that exercise on land does not.

How much swimming you need to do

The good news is that this does not necessitate hours in the pool. In our studies, swimming three times a week, for 30 to 45 minutes at a time, was enough to soften the arteries within three months.

Nor do you have to swim fast. The greatest health gains come simply from moving from doing nothing to doing a little; as you grow fitter you can slowly increase the effort, but you do not need to thrash up and down at speed to see your arteries change.

Which stroke is best for you

Front crawl and backstroke raise the heart rate well, but only if your technique is sound; without it, you will be worn out within a length. This is why so many people fall back on breaststroke, which is easier to sustain if your technique is limited. There is no firm evidence that any one stroke is better for the arteries, so the best stroke is simply the one you can keep up for 30 to 45 minutes, three times a week.

My advice to anyone taking up swimming later in life, or returning to it after years away, is to book a few lessons. We happily pay a personal trainer when we join a gym, yet almost no one thinks to hire a swimming coach – and it shows in the pool.

A handful of sessions spent correcting your breathing and body position will do more than anything to keep you swimming. And it is the swimming you keep doing, not the swimming you start, that softens the arteries.

There is one more reason I recommend it so often to older friends and colleagues. Where I live, in Texas, the summers are brutal, and exercising outdoors brings a real risk of overheating. In the pool there is no sweat and no overheating – and, just as importantly for an ageing body, no pounding of the knees, hips and ankles that forces so many runners to stop. It is an exercise you can keep doing for life.

Get your swimming technique right

Bad technique is the main reason people give up on swimming. If you are fighting the water rather than moving through it, your heart rate climbs, you are out of breath within a length, and you are out of the pool long before you have done your heart any good.

A few basics make most of the difference:

Breathing

The most common mistake is holding your breath underwater, then trying to breathe out and in during the split second your face is turned to the side. Instead, breathe out slowly and continuously into the water instead, so that all you have to do when you turn your head is take a breath in. Holding your breath allows carbon dioxide to build up, and that is what produces the panicky, gasping feeling most beginners recognise.

Body position

Sinking legs are the biggest drag on most amateur swimmers. If your hips and legs hang below the surface, you are effectively swimming uphill. Look down at the bottom of the pool rather than forward, and keep your head in line with your spine. The legs tend to follow.

Kicking

A big, bent-knee kick feels like effort well spent. It isn’t. It uses the largest muscles in the body, which demand a great deal of oxygen, and much of the water it moves goes forward rather than back. Keep the legs fairly straight, with only a slight bend at the knee, and drive the kick from the hip.

Pace

Aim for something you could keep up for half an hour, which is roughly 60 to 70% of your maximum heart rate, or a pace at which you could still get a short sentence out. A fixed figure in beats per minute is of little use, because maximum heart rate falls with age: for a 60-year-old that zone is around 95 to 110 beats per minute, for someone aged 40 it is nearer 110 to 125.