The frequency of your workouts is inversely related to the intensity of your training. That is, the more difficult your exercise is, the less often you should do the same activity. In fact, the American College of Sports Medicine encourages you to do five days of moderately challenging cardiovascular exercise or aerobics, but just three days of vigorously intense cardio.
Cardiovascular and Metabolic Benefits
The cardiovascular benefits you reap from frequent or intense exercise is relative to your current state of aerobic fitness. If you are a sedentary individual, sprinting for 10 minutes in one session, much less three times in a week, can cause injury, not to mention that you may give up on the exercise program. On the other hand, if you start with a 15-minute walk, three days a week, and gradually increase your duration and frequency to 30 minutes a day for five days a week, you will improve your cardiovascular fitness. That is, your heart and arteries need to do less work to circulate your blood, and your muscle cells are also better equipped to process oxygen and nutrients. At that point, increasing the intensity of your workout and decreasing your frequency enhances your cardiovascular and metabolic capacity. Consider running as fast as you can for 30 seconds then walking for 90 seconds, totaling 15 to 20 minutes; running up a hill, then down a hill, 10 times one day per week, and walking and jogging for 30 total minutes one day per week.
Calories and Stored Body Fat
Exercising at a high intensity level three days per week can burn as many calories as exercising at a moderate intensity every day. After exercise, your body must gradually wind down, returning your heart rate, body temperature and breathing rate back to pre-exercise levels. This takes a significant amount of calories, especially after a highly intense workout. Furthermore, high intensity training stimulates an increase in the production of enzymes which help break down fat.
Risks of Injury
Though highly intense exercise has many benefits, it places a tremendous strain on your muscles, bones, tendons and ligaments. If you do high intensity training every day, you are likely to suffer an injury which can derail your training program, with the result that you burn fewer calories, your cardiovascular system does not improve, and your muscle cells are not efficiently processing oxygen and nutrients.
Considerations
Instead of choosing between frequent sessions or more intense sessions, consider incorporating two highly intense sessions every week and two moderately intense sessions. Intense exercise should last up to 25 minutes while moderately intense exercise can last 45 to 60 minutes. By combining aerobic workouts at opposite ends of the intensity spectrum, you will reap the benefits of frequent exercise sessions and intense exercise sessions with less risk of injury.
References
- American College of Sports Medicine: Physical Activity and Public Health Guidelines
- "Exercise Physiology, Energy, Nutrition & Human Performance"; William McArdle, et al.; 2007
- "Strength and Conditioning Journal"; High-Intensity Interval Training: Applications for General Fitness Training; Brad Schoenfeld and Jay Dawes; December 2009
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