Your body needs energy 24 hours a day, seven days a week. You eat food, and your body breaks it down and stores what it needs so that it can be used for normal daily function and exercise. At rest, your body does not need as many calories, or energy, as it does when you are exercising. The amount of energy you expend during exercise depends on the duration, intensity and type of activity you are performing.
Duration
The longer that you exercise, the more energy you will expend. If you walk for 20 minutes one day and 60 minutes the next, you will burn more calories during the hour than you did during the shorter workout because your body is supplying energy throughout the workout. However, the amount of calories can decrease even if the time remains the same as you become more fit because your body has become more efficient and needs less energy to perform for the same duration.
Intensity
There is a positive correlation between the intensity of exercise and energy expenditure, according to the National Strength and Conditioning Association. The harder you exercise the more calories you burn during your session. To lose weight and improve health, exercise at a moderate to high intensity during cardio and resistance training to burn the maximum amount of calories. Even if you don't need to lose weight, you still want to keep intensity higher for the health and fitness benefits.
Cardio vs. Resistance Training
In general, you will burn more calories during a cardiovascular exercise session than you will during a resistance-training session. Obviously intensity and duration are factors, but this is a generally accepted principle, according to the American College of Sports Medicine. However, resistance training adds lean muscle tissue to your body over time. Muscle is metabolically active, so the more muscle you have the more calories you will burn -- even at rest.
Considerations
Your age and health play a role in energy expenditure during exercise. As you age, you lose lean mass and your metabolism naturally slows down, so you have to work harder to burn calories and maintain or lose body weight. If you have a chronic medical condition and/or are on medications, they can limit the type, duration and intensity of activities that you perform. For optimal energy expenditure and health, perform both resistance training and cardiovascular exercise.
References
- "ACSM's Guidelines for Exercise Testing and Prescription"; American College of Sports Medicine; 2010
- "Essentials of Strength Training and Conditioning"; National Strength and Conditioning Association; 2008
- Vanderbilt University: Weight Loss Ways: Cardio Exercise vs. Weight Training
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