Being regularly active can improve your mental well-being, reduce your chances of disease and increase your lifespan. The World Health Organization (WHO) recommends that adults get at least 150 minutes of moderate activity (brisk walking, easy cycling) or at least 75 minutes of vigorous activity (running, tennis), along with at least two strengthening sessions, per week. But only 73 per cent of adults meet these guidelines worldwide, and 51 per cent of Canadian adults are considered physically inactive.I’m a professor in Health Sciences at Simon Fraser University and I study how behaviours relate to health and disease. I also write a blog on the role health behaviours play in your health.What is physical inactivity?Physical inactivity is defined as not meeting the minimum guidelines for being active. Being physically inactive, however, doesn’t mean you’re not active at all. You could still be doing light activity, like general walking or household chores — just not moderate or vigorous activity. And in general, people who are inactive spend more of their time being sedentary. Sedentary activities are those of very little or no movement and include sitting, lying down and standing. For most people, the majority of sedentary time is spent sitting. Various studies report adults spend on average six hours per day sitting. But these studies are based on self-report. The few studies that have used direct measures of activity (such as accelerometers) indicate it may be closer to 10 hours of sitting per day.This is a concern as the WHO labels physical inactivity as the fourth leading modifiable risk factor for death. It’s estimated that with a 10 per cent increase in activity, 500 million early deaths could be prevented.Biological changes and health concernsFrom a biological perspective, being inactive is more than the opposite of being active. This is because sedentary activities result in unique physiological changes. When you sit, your metabolism slows down. This makes sense, as your energy needs are much lower. It’s not much different from a car engine shutting down at a stoplight. Prolonged sitting can lead to an accumulation of fats (triglycerides) in your blood. As your body needs less energy when sitting (or lying) down, production of certain enzymes goes down. One of those is lipoprotein lipase (LPL), which breaks down fats in the blood so muscles and organs can use fat for energy. In rodent studies, LPL decreased when the rodents were inactive. With continuous sitting over months and years, the excess fats can impair insulin and glucose metabolism, and increase your risk for Type 2 diabetes.Other health risks include weakened muscles. Muscles need movement to keep strong. If they’re not being used, they shrink and get weaker. Varicose veins and deep vein thrombosis can also result from the continually pooling of blood in the lower legs that comes with sitting. And over years, your risk for dementia, cancer, heart disease and early death rise.It’s quite common to wonder if being active can compensate for sitting. The short answer is yes — being active, even in the presence of long periods of sitting, is better for you than not being active. But it depends on how active you are, and how much you sit. In a study I co-authored, we found increased sitting was associated with early death regardless of how active you are. But the risk was worse for those who were less active. For those who met the WHO’s physical activity guidelines, sitting for more than six hours per day had the same risk as those who sat less than six hours per day but did not meet the guidelines.Managing sitting and sedentary behaviourWe’re not going to do away with sitting, nor should we. Sitting is needed to provide time for rest and recovery. Also, many tasks are more comfortably performed while sitting. At present, there isn’t a specific target for sitting time, other than to reduce how much siting you do. Standing is often mentioned as a solution. And the standing desk industry has exploded in recent years. While standing will result in less sitting, standing for long periods has a similar effect on metabolism as sitting. Other health concerns of prolonged standing include muscle fatigue, varicose veins and potential for greater risk for heart disease. Replacing sitting (or standing) with movement is the best solution. Our study found replacing 30 minutes of sitting with movement reduced risk for early death by two per cent in people who sat more than four hours per day. But getting up and moving for 30 minutes may not be possible in all situation, so it’s important to reduce continuous, uninterrupted sitting time. Breaking up sitting every 20-30 minutes with two minutes of activity (light walking, jumping jacks, squats or anything else) is enough to keep your metabolism running and manage insulin and glucose levels. To remind yourself, set your phone alarm every 20-30 minutes and get up and move. Other ways to decrease sitting time include taking phone calls while pacing in the office and holding walking meetings.While most people are aware that being active has health benefits, it’s also important to know that being sedentary has health risks. Physical inactivity can adversely affect your health.Scott Lear has received funding from the Canadian Institutes of Health Research, the Heart and Stroke Foundation, Novo Nordisk, Hamilton Health Sciences and the Robert Wood Johnson Foundation.