Most of us will count ourselves lucky if we make it to 80 without any major health concerns.  But for one older couple, only optimum fitness will do.

The grandparents of former Canadian rugby pro Phil Mackenzie have become Instagram famous — thanks to their unusually buff physiques at the grand age of 80 and 84. 

McKenzie, who boasts almost 500,000 Instagram and over 870,000 TikTok followers, has impressed social media users with clips of his elderly relatives' eye-watering fitness routines. 

In one video, Mr Mackenzie shows his grandfather lifting weights and claims he does '500 push ups three times a week', a regime even 30-somethings may struggle to achieve. 

In another, he lauds the sleep schedule, walking regime and diet essentials his Grandma swears by to live her 'fullest and most capable life'. 

'I adore how your parents are fit and a family that workouts together stays together', one follower said.

'They are rich…rich in health and life, the true wealth money can‘t buy,' a second commented. 

Taking to Instagram, Mr Mackenzie told his followers that key to his grandfather's success is 'focusing on strength training'.  

He said: 'One of my earliest memories of my Grandad involve him with a set of dumbbells working out. 

'To this day, my Grandad still lifts weights and does 500 push ups three times a week. 

'Strength training improves muscles mass, hormones, metabolic health and has a direct correlation to not just living longer but living a better life as you age.'

He added: 'He's also always eaten small meals unknowingly. 

'Ever since I can remember him, he has practiced a consistent and small form of calorie restriction. 

'Lastly, I have never met someone who appreciates the ability to move as much as he does. 

'He once told me he hates going to bed more than anything because he hates missing out on life. 

'There isn't a single day he takes his ability to move for granted. 

'He's a constant reminder that the moment you stop moving is the moment you stop living. 

'I'm going to do my best to follow his three rules for the rest of my life to make the most of it, just like he has.'  

It is well known that cutting calories makes people who are obese healthier through losing weight. 

But some studies have also suggested that the controversial fad of restricting calories could reduce the pace at which people age biologically. However, this research is still in its infancy, and many scientists say this isn't proven. 

Some experts believe restricting calories can lead to fatigue, nutrient deficiencies and harm fertility in men and women. 

In another video, Mr Mackenzie showcases the rules his Grandma has sworn to 'live her fullest and most capable life'. 

He says: 'Life can look very different at 80 if you do these simple things. 

'She is so inspiring and not only has she shown me that at 80 a 20 inch box jump in flip flops is still possible, but most importantly she’s shown me how capable we can be as we age if we prioritize our health now.' 

Her tips include ample sleep, 'always avoiding processed foods' and 'walking everywhere — whether it's a five minute walk to the grocery store or 10 kilometre trip to the shops'. 

He added: 'It's not just the fact she's walking but how fast she's walking that has helped her stay so capable for so long. 

'Research has shown there's a direct correlation between faster walking speeds and longevity.

'It's no surprise my Grandma can easily keep up with her great grandkids.

'Both my grandparents have also stayed consistent with their bedtime and wake up times. 

'Irregular sleep patterns have been linked to higher risks of hypertension, obesity and diabetes — all of which are risk factors for mortality.'

Keeping fit has long been lauded as vital for longevity, as it can help with maintaining a healthy weight, boosting metabolism and increasing muscle mass. 

Being too fat increases the risk of a swathe of chronic illnesses, such as heart disease, type 2 diabetes and some cancers, while being frail can see minor ailments become severe.

But working out boosts cardiovascular health, muscle and bone strength and reduces inflammation. 

Chronic inflammation is a hallmark of ageing that is thought to be responsible for a swathe of age-related illnesses and shortened lifespan. 

It also improves insulin sensitivity, which is vital to protect against type 2 diabetes.

As well as these physical benefits, exercising supports mental health by boosting mood and lowering stress and anxiety levels.

Previous research has also suggested a link between lack of sleep and increased risk of obesity and type 2 diabetes.

The most common causes of insomnia are thought to be anxiety, depression, alcohol, caffeine, recreational drugs and working shifts.

While adults need between seven and nine hours of sleep, children are advised to have between nine and 13, the NHS recommends.

The health service estimates it takes most people 14 minutes on average to nod off.

Studies suggest that at least 30 per cent of the issues GPs face are directly or indirectly related to sleep. 

Yet just one Briton in ten talks to their doctor about insomnia, despite 30 per cent taking medication to try to deal with it.