Fitness trackers and fitness equipment can tally your calories burned while exercising, but they’re not always accurate. “Using a variety of sources and taking a ‘midpoint’ might help keep you honest,” says Hilaton. “I think it is important to keep in mind that all of these estimates of calories burned are just that: estimates. There are a lot of variables that go into the actual number of calories burned by any given individual in any exercise beyond speed and duration.” For a starting point, calculate your numbers with our Calories Burned Running Calculator.
A recent randomized crossover trial of lower-intensity or high-intensity exercise showed decreases in clinical SBP with both types of exercise. However, there was no decrease in mean day or nighttime ambulatory BP with either form of exercise.42 Aerobic interval training (AIT) combines episodes of high-intensity with episodes of low-intensity aerobic exercise. At least two randomized studies have suggested an advantage of AIT over continuous aerobic exercise.43,44 Some patients, of course, have limited ability to use their legs, and upper extremity aerobic exercise also has been shown to lower BP.45
You can get more specific with your aerobic interval training and use heart rate since it's an excellent indication of how hard you are working. Let's use jogging on a treadmill as the aerobic activity in this example. For example, if your heart rate is at 70% of your predicted maximum when you jog at 6 mph, then start at that speed and either increase the speed or elevation so that your heart rate increases to 85% or even 90% for one minute, then back to your usual jogging speed for three minutes to elicit a heart rate of 70%. Start with a 1:3 work:active-rest ratio. That's a good starting point, and as you increase the work intervals and decrease the active-rest ratios like in the examples above, you'll notice that your conditioning improves so that your heart rate will be lower at the higher speeds.
Walking is one of the simplest ways to get fit and maintain heart health. The American Heart Association's guidelines for physical activity indicate that healthy adults should aim to walk a minimum of 150 minutes per week, or 30 minutes every weekday. Walking seven days per week will burn more calories, and you can add challenges to your walking workout that make it more of a cardiovascular or strengthening exercise.
I recommend using a pedometer, or better yet, one of the newer wearable fitness trackers, to keep track and find out how far you normally walk. At first, you may be surprised to realize just how little you move each day. Tracking your steps can also show you how simple and seemingly minor changes to the way you move around during the day can add up. Plus, it’s motivating to see your steps increase throughout the day, which makes it easier to push yourself a little farther to reach your 10,000-step goal.

"Oxygen consumption" describes the process of muscles extracting, or consuming, oxygen from the blood. Conditioned individuals have higher levels of oxygen consumption than deconditioned individuals ("couch potatoes") due to biological changes in the muscles from chronic exercise training. For example, a deconditioned individual might have a maximal oxygen consumption of 35 milliliters (ml) of oxygen per kilogram of body weight per minute (ml/kg/min), whereas an elite athlete may have a maximal oxygen consumption up to 92 ml/kg/min! Values like this are expressed as VO2 (volume of oxygen consumed) and can be measured with special equipment in a laboratory.
Researchers at Southern Methodist University took a close look at the most common equations used over the past 40 years. And surprise! They found two major problems: First, the sample sizes that these equations were based off of were way too small (only six people for one method), and only included men. Second, this data didn’t take into account that people of different sizes expend energy at different rates (for instance, heavier people burn fewer cals per pound when walking the same distance as those who weigh less). As a result, when the researchers put these two equations to the test, they found that their calorie estimates were too low in a whopping 97 percent of cases.
Classes are generally rated as beginner, intermediate, and advanced. Choose the level that fits your condition. It's no fun taking an advanced class if you're a beginner. It will be hard and frustrating and you won't enjoy the experience. Watch the class or speak with the instructor to help you decide what's right for you. Sometimes it comes down to the class time that fits your schedule, but just be sure to not get in too far over your head.
Every session of aerobic exercise should include a warm-up and cool-down. The warm-up period should not include static stretching, but should instead be a gradual increase in pace and intensity of the exercise. This allows for the body to increase blood flow to the muscles, and decreases the likelihood of a muscle or joint injury. The warm-up should last between 5 and 10 minutes. The cool-down session should last a similar amount of time as the warm-up, with the pace gradually decreasing. Stretching exercises would be appropriate after aerobic exercise.
Knowing a bit about the health benefits of walking can also help you stay on track. Not only can walking benefit your heart, bones, and joints, it can also prolong your life. In a 10-year study of 650,000 adults over 40, those who got 75 minutes of moderate activity, like walking, weekly, lived on average, nearly two years longer than their sedentary counterparts. Walkers who logged just over an hour a day gained four and a half years!
I defined aerobic exercise for you in the introduction. It's any activity that stimulates your heart rate and breathing to increase but not so much that you can't sustain the activity for more than a few minutes. Aerobic means "with oxygen," and anaerobic means "without oxygen." Anaerobic exercise is the type where you get out of breath in just a few moments, like when you lift weights for improving strength, when you sprint, or when you climb a long flight of stairs.
A single activity can include elements of both aerobic and anaerobic exercise. For example, interval training, where you alternate cycles of low-intensity (aerobic) and high-intensity (anaerobic) work during the same workout, has elements of both. So does a game of tennis where you might sprint at one moment (anaerobic) and then move less aggressively for several minutes (aerobic) as you hit ground strokes from the baseline. 

Aerobic fitness is a stronger independent predictor of morbidity and mortality compared with physical activity. However, it is difficult sometimes to delineate between the individual effects of aerobic fitness versus total weekly caloric energy expenditure (physical activity). Furthermore, measuring total weekly energy expenditure in both free-living and structured exercise is much more difficult than measuring aerobic fitness.

It doesn't take all that much aerobic exercise to accrue lots of fitness and health benefits. There are two physical activity recommendations to choose from in the United States. One is the Surgeon General's "lifestyle" recommendation, where you can accumulate activity and incorporate it into your day (a nice way to save time for busy people), and then there's the formal "workout" recommendation from the American College of Sports Medicine (ACSM).