What is sedentary behaviour?
Sedentary behaviour is any time spent sitting or lying down while awake, using very little energy. Working at a computer, driving, watching television and scrolling on a phone all count. Sleep is not a sedentary behaviour.
It is not the same thing as being physically inactive. Someone can run for half an hour before work, meet the recommended national physical activity guidelines, but still spend most of the remaining waking day in a chair. Over the past two decades researchers have come to treat high amounts of sitting as a risk to health in its own right — something to think about alongside exercise, not instead of it.
Why does sitting affect the heart?
When you sit for a long stretch, the large muscles of your legs and back are essentially switched off. Those muscles do a great deal of important work for metabolism: they draw glucose out of the bloodstream and help clear fats from it. When they stay idle for hours, blood glucose and blood fats remain higher after meals than they otherwise would, blood flow through the vessels slows, and the body's regulation of blood pressure is affected.
Repeated across days and years, these small shifts are thought to contribute to insulin resistance, raised blood pressure and unhealthy cholesterol levels — the changes that underlie type 2 diabetes and cardiovascular disease. Prolonged sitting has also been associated with some cancers, although the evidence there is less settled.
Does doing exercise cancel it out?
Not entirely, and this is the finding that surprises most people.
Being active clearly helps and is certainly better than doing no activity. People who do a lot of moderate to vigorous intensity activity (e.g. brisk walking, jogging) carry much less of the risk associated with long sitting hours, and in the most active people a large part of the effects of prolonged sitting appears to be offset. But most of us do not reach those levels on a daily basis, and among people who exercise moderately, long uninterrupted sitting still appears to matter for our physical health.
The practical message is not that exercise is pointless — it plainly is not. It is that a workout does not buy a pass for the other fifteen hours of the day. Both parts count.
How much sitting is too much?
There is no official Australian limit on total sitting time, and no threshold at which sitting suddenly becomes harmful. The Australian 24-hour movement guidelines for adults instead recommend breaking up prolonged periods of sedentary behaviour as often as possible, and accumulating several hours of light-intensity activity into the day, alongside the usual targets for moderate and vigorous intensity activity.
That emphasis is deliberate. How sitting is accumulated seems to matter as much as the total duration. Several unbroken hours appear to place more strain on the body than the same number of hours interrupted regularly with brief activity — which is encouraging, because the interruptions are the easier part to change.
Where does the sitting add up?
Work is the obvious source for anyone in a desk-based job, but it is rarely the whole story. Add the commute, the evening in front of a screen, and the weekend hours that pass sitting down, and the total climbs quickly — often well beyond what people estimate when asked.
Sitting is also not spread evenly across the population. Office workers, drivers and machine operators accumulate more of it through work, and people living with chronic illness, pain or limited mobility may have fewer opportunities to break it up.
How can I sit less?
None of this requires a gym membership, special equipment or extra hours in the day. It is mostly a matter of rearranging time you already spend.
- Aim to move at least once every 30 minutes. A minute or two on your feet and preferably moving is enough to interrupt prolonged sitting.
- Take phone calls standing or walking.
- Use the stairs where you reasonably can.
- Get off public transport a stop early, or park a little further away.
- Suggest a walking meeting instead of a meeting room.
- Stand or move about between episodes or during ad breaks.
- If you have a sit-stand desk, alternate through the day rather than standing for all of it — standing still for hours may bring its own problems.
If getting up to stand or walk is difficult (e.g. because you use a wheelchair, have pain or have limited mobility) the same idea still applies: try to change position and move in ways that feel safe and manageable for you. This might include moving your arms or upper body, doing exercises while seated, or shifting your position regularly. An accredited exercise physiologist can help you find activities that suit your needs and abilities.
Reducing the time you spend sitting is not a replacement for regular exercise, and importantly, it doesn't need to become another task on your daily to-do list. It is about making small changes to the way you already spend your day — for example, standing up more frequently, moving around, or changing position more often. These changes can be a simple, realistic way to support your long-term heart health and help your body better manage blood sugar and metabolism.