From Apple Watches to Oura Rings, many of us have become obsessed with tracking our health to help us live longer—but experts say there is one powerful metric we could be overlooking.

Whilst 'longevity' has become somewhat of a buzzword in recent months, experts say we shouldn't just be focusing on cardiovascular fitness, blood pressure and sleep data to boost our lifespan, but muscle health also. 

'Musclespan is the way in which we support strength and healthy ageing,' Dr Gabrielle Lyon—who has spent years studying how muscle strength impacts ageing, told Women's Health. 

'It's about living as long as you can with healthy skeletal muscle,' she added. 

This group of muscles refers to those which pull on bones, contracting and relaxing,  to produce all body movements.

According to Dr Lyon, the strength and mass of these muscles is a good indication of how long you will live. 

'Muscle is the key because it is a metabolic and endocrine organ,' she added, meaning that it doesn't just enable movement but is also related to insulin sensitivity, metabolic health, as well as the immune system. 

She continued: 'It's not if, but when, illness strikes because it happens to all of us. 

'If you are prepared with both strength and mass then you are much more likely to be able to overcome life's challenges.'  

The reason for this is because these muscles produce hormones called myokines which play a powerful role in reducing inflammation, protecting against disease and promoting longevity. 

A recent study published in Endocrine Reviews even found that myokine may be the reason why regular exercise significantly decreases the risk of some cancers, heart disease and even dementia. 

'These powerful messengers allow muscle to 'talk' to other organs, including the brain tissue, liver and immune system, helping regulate vital processes like blood sugar control, metabolism, mood and brain health,' Dr Khemani, a clinical professor at Stanford University specialising in perioperative care of surgical patients, said. 

'Because of this, muscle is deeply connected to metabolic health, cognitive function, longevity and disease resilience making it one of the most powerful predictors of how long and how well one will live.' 

Whilst workouts like interval training are essential to boost musclespan and maintain muscle fibres—and a healthy diet and restorative sleep are integral—you can begin tracking your baseline musclespan at home. 

One of the best indicators of muscle strength is your ability to carry out functional movements—such as squats, push-ups and pull-ups, which Dr Lyon believes everyone should be able to do. 

Research has shown that push-ups are a particularly good measure of musclespan overtime, with a study finding what men would could do 40 push ups had a lower risk of death than those who could only do 10. 

And it is thought that women would experience similar benefits with even fewer reps. 

As such, Dr Lyon recommonds aiming for 10 push-ups, 1 unassisted pull-up and at least 25 squats as a benchmark. 

A simple one-minute test could also tell you if you're going to die earlier than your peers, Dr Lyon claims. 

The grip test—which measures the force with which someone can squeeze an object—has long been considered an accessible assessment of physical health. 

Strong grip strength has been linked to a reduced risk of dying from a number of age-related disease—from heart disease and type 2 diabetes to arthritis and certain cancers. 

And weak grip strength is a sign of a detrimental level of muscle loss known as sarcopenia—a disease characterised by a decline in muscle mass and function. 

Now, experts say that grip strength is a good barometer of how everything else will weaken.

To combat this Heather Milton, an exercise physiologist at New York University, recommends implementing strength training which targets all major muscle groups  twice a week into your exercise routine. 

She said: 'Choose a weight that, by the last repetition, you could probably do only about one or two more times before failure, or before your from breaks.' 

Training in this range should put sufficient stress on the muscles so they have to adapt, she added. 

But, she warned, doing higher-intensity exercise or lifting which targets the same muscle groups every day without adequate rest, which gives the muscles time to repair and grow, could be detrimental. 

 'That's why sleep is imperative: when we sleep, the hormones that create those adaptations are at their peak.' 

Ensuring your VO2 max—a measure of how much oxygen the body uses when exercising—falls within a healthy range for your age and gender can also provide insights into overall muscle health, and therefore how long you will live.

Dr Lyon also recommends having a blood test every three to four months to monitor blood markers related to metabolic syndrome—like blood sugar level, cholesterol and triglycerides—a group of health problems that increase the risk of heart disease, stroke and diabetes. 

She said: 'All of those are indicators of metabolic syndrome, which is in actuality unhealthy skeletal muscle.' 

'And whilst msuclespan isn't built in a day, the data supports that you're never too old—and also never too young—to improve muscle health.       

'Muscle health, strength and mass have emerged as some of the most robust predictors of healthy aging.'