When I write about health-related issues in this column I routinely use terms like exercise, physical activity and fitness. Some people have asked why I use these different words since they all have a similar meaning. That is an excellent question since, although these terms are related, they have different applications for health and wellness.

Physical activity (PA) is defined as any movement produced by muscles that expends energy. PA can be classified as occupational, what you do at work, and leisure time, what you do in your free time. Occupational PA can vary greatly depending on the job, but it is low for most of us who spend much of our work day sitting. Leisure-time PA is all activity outside of work. This is of great interest to researchers since it reflects how we chose to spend our time. Physical activity can be measured pedometers, which count the steps you take, or other motion sensors that are wearable, which measure how much you move.

Exercise is a type of physical activity that involves planned, structured and repetitive movement to improve or maintain physical fitness. Physical fitness, then, is a set of attributes that relate to the ability to perform physical activity and exercise. The components of physical fitness include endurance, strength and flexibility. Basically, participation in physical activity and exercise improves your fitness and the greater your fitness, the better able you are to participate in physical activity. This is true for completing occupational tasks as well as traditional exercise, such as jogging or lifting weights.

The good news is that both physical activity and exercise have health and fitness benefits. Physical activity can vary in intensity, from light (slow walking), moderate (brisk walking) or vigorous (exercise like running). The 2018 U.S. Physical Activity Guidelines recommend that, at a minimum, all adults participate in moderate-intensity physical activity for 2 hours and 30 minutes per week or vigorous activity for 1 hour and 15 minutes per week along with strengthening exercises at least 2 days per week. You can meet this recommendation by going for a brisk walk for 30 minutes on 5 days per week or running for 25 minutes on 2 days per week or some combination of the two. Additional benefits come from doing more, either higher intensity or longer duration activity.

Vigorous exercise is the best way to improve fitness while moderate-intensity activity is strongly linked to health benefits. Fitness benefits result from adaptations in the heart and muscles, which get stronger and become better able to resist fatigue. These changes also lead to health benefits including lower blood pressure, cholesterol and glucose as well as helping with weight loss and weight control.

Research suggests that health and fitness benefits also result from light-intensity or intermittent activity, especially if it replaces sitting. At home or at work, the more time you spend sitting, the poorer your health, even if you exercise every day. One study shows that getting off the couch and stepping in place during TV commercials results in nearly 25 minutes of activity per hour and burns about 150 calories, compared to 80 calories just sitting the entire time. You won’t get in great shape doing this, but it is a simple way to increase your overall activity.

With this is mind, a good recommendation is to reduce sitting time in favor of light activity – stand while you read the paper or walk around while you talk on the phone – and participate in moderate or vigorous activity each day by going for a brisk walk or doing other exercise, including strength training.