Cardio exercises burn a significant number of calories and improve your cardiovascular fitness. The effect on your heart varies with the intensity of the exercise. During exercise, your heart responds to your body's demand for more oxygen. The higher the demand, the greater your heart rate will be. External factors such as environmental conditions also play a role. Taking your pulse will help you measure your heart rate and the intensity of your exercise.
Exercises can be classified by their effect on your heart rate, based on your heart's maximum rate. Your maximum heart rate is 220 minus your age. Light exercise is calculated as 50 to 70 percent of this figure. Moderate exercise will raise your heart rate to 70 to 80 percent. The most intense exercise will challenge your body with heart rates from 80 to 90 percent of your maximum heart rate.
Factors Affecting Heart Rate
Your heart rate is elevated by the most vigorous exercise. Vigorous exercises engage large muscle groups. The demand for oxygen skyrockets, causing your heart to beat faster to keep up with the needs of your body. You may find that other factors can affect your heart rate during exercise, such as the use of stimulants like caffeine. Weather conditions, such as high humidity, will also impact heart rate. In these situations, your body isn't receiving as much oxygen with each breath. Your breathing rate will increase, as will your heart rate.
Adapting to Activity
If you exercise regularly, you'll find that your body adapts to your activity and becomes more efficient over time. These adaptations affect the heart and heart rate. Your heart is like any other muscle that you train -- intense activity will increase its size and strength. As it becomes stronger, it will beat more forcefully to deliver blood to body tissues. During exercise, your heart rate and blood pressure will increase. How much it increases is a matter of exercise intensity.
Measuring Exercise Intensity
You can gauge exercise intensity, and thus its impact on your heart rate, by looking at calorie burn. According to the American Council on Exercise, a 160-pound person will burn about 145 calories an hour while walking at a leisurely 2 mph. The same individual, rollerblading vigorously, will burn 871 calories an hour. The difference lies in the muscle activity. While rollerblading, you use both your upper and lower body. Your abdominals are constantly working to keep you balanced. Your heart rate soars to supply oxygen. Similar activities include cycling, running and jumping rope. If your aim is to raise your heart rate to performance levels, these exercises will provide the most intense workout.