In 1966, five young, healthy men did something quite radical. They volunteered to do absolutely nothing. For three weeks, they lay flat on their backs in a research facility in Dallas – no walking, no standing, no sneaky laps to the fridge. Just pure, uninterrupted bed rest. It sounds like a dream holiday to some, but the consequences were more nightmare than nirvana.

The Dallas Bed Rest and Training Study was designed to explore what happens to the heart and cardiovascular system when physical activity is completely removed from the equation. What it revealed changed the way we understand exercise, health and ageing.

After just three weeks of doing nothing, these otherwise healthy 20 year olds experienced a 27 per cent drop in their VO₂ max – a measure of how much oxygen your body can use during intense exercise and the gold-standard marker of cardiovascular fitness. To put that into perspective, that’s like ageing your heart by a whopping 30 years in just 21 days!

Their cardiac output plummeted by 26 per cent, and their stroke volume (the amount of blood pumped with each heartbeat) fell by 31 per cent.

Even at submaximal efforts – think cycling gently or climbing stairs – their hearts had to work significantly harder. Heart rate, blood pressure and myocardial oxygen demand were all up. Their cardiovascular system had essentially gone from a Formula One racing car to a knackered second-hand hatchback in 21 days.

Now, here’s the beautiful twist in the tale. After the bedrest phase, the men embarked on eight weeks of structured endurance training. The result? Their VO₂ max increased by 45 per cent, stroke volume surged by 48 per cent, and cardiac output returned to – and even surpassed – baseline. In other words, the damage done by three weeks of being sedentary was reversible, but only through serious graft.

The study was a bombshell. It debunked the then-popular medical approach of prescribing prolonged bed rest following conditions such as heart attacks. Within years, cardiac rehab became a thing.

The lesson? The heart hates inactivity – and it thrives on being pushed.

30 years later: The heart remembers

Fast-forward 30 years and the same five men, now in their 50s, were rounded up again by Dr Benjamin Levine and colleagues from the Division of Cardiology, University of Texas Southwestern Medical Center.

This time, the men weren’t prescribed bed rest. But they were studied to find out how ageing had affected their hearts.

Surprisingly, VO₂ max had only declined by 12 per cent over three decades – far less than the 27 per cent nosedive from those original three weeks on their backs. It turns out ageing can be far less catastrophic for your heart than idleness.

And when these men trained again – albeit at a gentler pace and for longer duration – they regained nearly all their cardiovascular fitness from their younger days. Ageing hadn’t robbed them of their heart’s capacity to bounce back. It had just made the climb steeper.

They were followed up after another ten years and, now in their 60s, things had started to unravel. Hypertension had crept in, arrhythmias emerged and one had undiagnosed cancer.

The lesson here is crystal clear – the earlier you intervene, the more you preserve the heart’s plasticity.

The modern-day heart reboot

Let’s jump ahead to 2018, when the same research group from the University of Texas Southwestern Medical Center decided to answer a burning question: can we actually reverse the cardiac ageing caused by years of sitting and stressing and skipping workouts, especially in middle age?

This time, they recruited 61 healthy but sedentary middle-aged adults and split them into two groups. One got two years of light stretching and yoga – the ‘do no harm’ control group. The other group got a structured, periodised exercise regime that included:

·      four to five days per week of training
·      moderate aerobic work at zone 2 (the backbone of endurance)
·      high-intensity intervals in the form of the heavily researched Norwegian-style 4×4 protocol (four minutes of high-intensity exercise getting the heart rate to 90 to 95 per cent of maximum, followed by three-minute light recovery, repeated for four intervals)
·      long endurance sessions
·      strength training (twice per week).

This wasn’t a quick-fix boot camp. It was a two-year study of pretty serious training. And after two years, the results were pretty bloody impressive.

The exercise group saw an 18 per cent increase in VO₂ max – a massive win in middle age, and a definite boost to their longevity potential. (As a measure of oxygen use and cardiovascular health, your VO₂ max is the single biggest predictor of how long you’re going to live.)

But the real prize was deeper: their hearts became more compliant, more elastic and more youthful. Left ventricular stiffness, a key indicator of heart health, dropped. Heart size increased. Stroke volume improved. Resting heart rate decreased. They didn’t just feel younger – they were younger, at a cardiac level.

The control group? Nada. In fact, they edged closer to frailty with increased left ventricular stiffness and declining function. It’s a stark reminder to use it or lose it.

Cardiac stiffness is a key driver of heart failure and a common and devastating condition in older adults. Once stiffness sets in, the heart can’t relax properly or fill efficiently. You tire easily. You puff going up stairs. And, eventually, your quality of life shrinks to match your cardiovascular reserve.

But here’s the kicker: if you intervene in middle age, you can prevent this trajectory. The heart, it turns out, is still beautifully plastic in your 40s and 50s – if you give it the right nudge. And that nudge doesn’t have to be a marathon. This study’s protocol mirrored public health guidelines of 150 to 180 minutes of exercise per week – plus a dash of high-intensity magic. It was doable and sustainable. And it worked.

Edited extract from The Hardiness Effect: Grow from stress, optimise health, live longer by Dr Paul Taylor (Wiley, $34.95), available at Amazon and leading retailers. Dr Taylor is a keynote speaker, podcast host and thought leader with post-graduate qualifications in psychology, exercise science, nutrition and neuroscience. Driven by the belief that we can grow from stress and live longer, healthier lives with the right habits, Dr Taylor helps individuals and teams unlock the power of psychophysiological hardiness to perform at their best.