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.
Prof Hiro Tanaka is director of the Cardiovascular Ageing Research Laboratory at the University of Texas at Austin. He was talking to Will Stoddart