While most people understand the dangers of smoking, the health risks associated with prolonged sedentary behaviour, such as sitting at a desk for work, are less known.

But health risks for desk-bound individuals are high –  so should they exceed WHO's exercise guidelines to compensate for this inactivity? One study has shown that it's beneficial, but experts warn against too much activity.

WHO's recommendations for adults under age 65:

• 150-300 mins of moderate-intensity, or 75-150 mins of vigorous-intensity physical activity, or some equivalent combination of moderate-intensity and vigorous-intensity aerobic physical activity every week.

• Undertake muscle-strengthening activity (such as weights, core conditioning) at moderate or greater intensity on two or more days of the week.

In a study published in the British Journal of Sports Medicine scientists have concluded that those who are sedentary for long periods can offset health harm by exceeding WHO's weekly exercise recommendations.

The study, which involved more than 44,000 people from four different countries, reveals that a high daily tally of sedentary time (defined as ten or more hours) is linked to a significantly heightened risk of death, particularly among physically inactive people.

But 30 to 40 daily minutes of moderate to vigorous-intensity physical activity substantially weakens this risk, bringing it down to levels associated with very low amounts of sedentary time.

These new guidelines reflect the mounting evidence sedentary behaviour leads to a heightened risk of chronic health issues, such as heart disease, cancers, depression, and early death.

Exercise physiologist Nicole Davies explains that sedentary behaviour has implications for the heart, body, brain and even social wellbeing. But expecting people to exceed the guidelines may be a deterrent, and all exercise is better than none.

"The recommendations by WHO, which is consistent with the American College of Sports Medicine, is a lot of activity!

"My feeling is that if you recommend higher than this, people will just think it's too hard and do nothing. 

"When we see clients attend two classes a week consistently …we have seen great results and real changes in people's lives.

"Keen clients who were going to come four times a week and do running in between – they're lucky to last two weeks before they give up."

So, what are the health implications of prolonged sitting and how much exercise is enough?

"This is a very broad topic, with many interacting dimensions, but there are specific health risks of a sedentary lifestyle that stand out.

"They can be addressed by changing your habits to have a more structured and specific activity in your life."

Risks to heart health

A sedentary lifestyle affects heart health, which directly increases the risk of heart disease, blood pressure, developing diabetes and stroke, explains Ms Davies.

"A lack of physical activity reduces the normal functioning of your heart and how effectively the blood vessel cells release important chemicals, which easily relax the blood vessels and reduces the stiffness of these critical arteries.

"The result is that your general exercise tolerance is poor. When you do move or exercise, it takes more heart effort than it should, and your blood pressure rises more than it should, further increasing your risk of heart attack and stroke".

Fortunately, the body can adjust and responds to exercise over time.

"So, if you exercise regularly, it responds by improving your heart function, your exercise tolerance and the function of the blood vessels to the major organs in your body, such as kidneys, legs and arms.

"150 minutes of moderate exercise (meaning that you are 'somewhat puffed' or 'cannot carry on a conversation during activity') a week is enough for exercise's cardio effects."

"This does not have to be done in one go and can be spread to five 30-minute sessions a week.

"If for you it is walking, walk at a pace that makes you puffed, and it is hard to maintain a conversation with your walking partner."

Risks to the body

Reduced muscle strength due to a lack of strengthening exercises is common, says Ms Davies.

"Most people are not strong enough for what they ask their bodies to do in everyday life, which means that when you go for that walk, climb uphill, do the gardening on the weekend or lift your child or grandchild, it's more effort than it should be and you are more likely to injury yourself."

It can be a vicious cycle, where people don't feel strong enough, so they do less and get weaker. But increasing muscle is crucial in the battle against diabetes, explains Ms Davies.

"Muscle mass is a primary site of GLUT4 insulin transporters, which take the glucose from the bloodstream and bring it into the muscle cells, regulating your blood glucose level and effecting your insulin sensitivity.

"Strengthening exercise both increases the number and effectiveness of these sensors."

Risks to the brain

Exercise, especially strengthening exercise, helps to preserve and improve brain function as you age.

"This is due to the protection of the cardiovascular system and the function of the small blood vessels in the brain.

"People with higher grip strength, a proxy for overall body strength, performed higher in memory tests and reaction time."

In a study, those who lifted weight at least once a week showed significant cognitive function improvements, such as attention.

"It seems to be because strength training releases several chemicals into the brain, which improve the health of nerves and brain cells."

Social risk

A risk that's not so obvious is the impact of social and mental wellness for those who don't exercise.

"A trip to your favourite exercise session is often accompanied by a quick coffee with an exercise partner or a friend after your session.

"A conversation with the instructor or other participates in the class also allows you to stretch your social 'muscle' and feel like you are not alone and part of the community.

"We have seen the importance of this after the long lockdown in Melbourne. The loss of interaction for our clients with the staff, the other clients and the staff themselves were a major part of the return to a degree of normality after a long period of social isolation."

So, what's ideal for adults who want to reduce the health harm of sitting for long periods?

"The demands of leading an active lifestyle are not complicated or arduous, nor do you have to train like an elite athlete to see the benefits!"

Aim for two 30-minute strength-based training sessions, which work on the major muscle groups, and 150 minutes of moderate exercise every week, advises Ms Davies.

"It's enough and will lead to the life you deserve."