The new year is a time when many plan to shape up after the excesses of the festive period.
Now there is good news for those who fear it might be too late in life to improve their fitness.
People into late middle age can reverse or reduce the risk of heart failure caused by decades of sedentary living by exercising, a study has found.
But there is a catch - it takes two years of aerobic exercise, four to five days a week, researchers said.
The study, published in the journal Circulation, analysed the hearts of 53 adults aged 45-64 who were healthy but had no history of exercising regularly.
Research has shown that sedentary behaviours - such as sitting or reclining for long periods of time - increase the risk of heart disease.
The study's participants were divided into two groups, with one following an aerobic exercise routine that progressed in intensity over the two years and another doing yoga, balance training and weight training three times a week, also for two years.
The aerobic exercise group showed an 18% improvement in their maximum oxygen intake during exercise and a more than 25% improvement in "plasticity" in the left ventricular muscle of the heart - both markers of a healthier heart.
However, the benefits were not seen in the second group.
Dr Benjamin Levine, lead author of the study and the founder and director of the Institute for Exercise and Environmental Medicine, a joint programme between Texas Health Resources and UT Southwestern Medical Center Dallas, Texas, said: "The key to a healthier heart in middle age is the right dose of exercise, at the right time in life.
"We found what we believe to be the optimal dose of the right kind of exercise, which is four to five times a week, and the 'sweet spot' in time, when the heart risk from a lifetime of sedentary behaviour can be improved - which is late-middle age.
"The result was a reversal of decades of a sedentary lifestyle on the heart for most of the study participants."
What the study's participants did
Participants exercised generally in 30-minute sessions, plus a warm-up and cool-down.
Their routine included:
- One high-intensity aerobic session, such as four-by-four interval training where participants did four sets of four minutes of exercise at 95% of their maximum heart rate followed by three minutes of active recovery at 60-75% peak heart rate
- Two or three days a week of moderate intensity exercise (where exercisers sweat but can still carry on a conversation)
- At least one weekly strength training session
- At least one long session of aerobic exercise a week, such as an hour of tennis, cycling, running, dancing or brisk walking
They built up to those levels, beginning with three 30-minute moderate exercise sessions for the first three months after which high intensity exercise was included.
Dr Levine told the BBC the take-home message from the research is that exercise needs to be a part of people's personal hygiene, like teeth brushing.
"It's not something that gets added on to the end of the day: You brush your teeth, you change your clothes, you eat food and drink water.
"You do these things for personal hygiene. Exercise is equally important. You need to find ways to incorporate it into your daily activities."
Dr Richard Siow, vice-dean for the faculty of life sciences and medicine at King's College London and director of ageing research at King's, told the BBC the study was valuable in that shows we can delay cardiovascular ageing.
He said it provided further evidence that "we can, in a way, rejuvenate or make the cells in the heart, and also in the blood vessels for that matter, resemble younger cells through an exercise programme".
"I think that's a very important take-home message for those of us who may have a doom and gloom view there's nothing we can do about it. Yes there is, we can start by getting off the couch to have a more active lifestyle."
Little change after 65
Dr Siow said the study also had ramifications for conditions relating to cognitive decline, such as dementia, because improved heart function facilitates blood flow to the brain.
"The wider ramifications of this study for healthy ageing need to be explored," he said.
Previous studies have shown improvements in heart elasticity in young people after a year of training, but little change if the training was started after the age of 65, the report's authors said.
They said the aerobic exercise regimen should be started before the age of 65 when the heart appears to retain "plasticity" and the ability to remodel itself.
Dr Levine told the BBC his team would next look at whether the same kind of improvements shown in the study can be made in people at high risk of heart failure, such as those with high blood pressure or diabetes and those who are obese.
However, researchers said there were a couple of limitations to the study.
One was that volunteers were willing and able to participate in an intensive exercise regimen, which may not be the case for the general adult population.
Another potential limitation was that most of the study's participants were white and it was not clear whether the results would apply to other racial groups, researchers said.
It also does not mention diet or other factors that can affect health, such as pollution.
"It needs to be taken into the context of a healthy lifestyle as well," Dr Siow added.
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