The Right Combination of Aerobic Intensity and Duration

The term "aerobics" became popular when a book with that title became a national best seller. Aerobic exercise, as the world knows, is beneficial for both weight control and cardiovascular fitness. Today most bodybuilders incorporate aerobic workouts into their contest-preparation training.

One misconception about aerobic exercise has to do with the intensity necessary to obtain the required benefits. Generally, the greater the relative training intensity, the faster the rate of improvement. What people don't realize is that the upper level of the training effect appears to be the same-it just takes more time to get there when you're training at a lower intensity.

Just how hard you should work out appears to be linked to the goals you desire. Higher-intensity exercise may be more beneficial for weight control, while lower-intensity aerobics may be just as beneficial for cardiovascular fitness and performance.

Any appropriate exercise program, however, must consider the major factors related to training improvement:

1 intensity of exercise

2 duration of exercise

3 frequency of exercise

4 type of exercise

5 initial fitness level. The information in this article applies to all levels of fitness.

For optimal results in attaining a higher level of fitness, you would want to exercise daily. For maintaining already-achieved adaptations, a lower frequency-several times a week-will work as long as you maintain the intensity. Training-induced physiological changes depend primarily on the intensity of the overload. Exercise intensity reflects both the caloric cost of the work and the specific energy systems activated. There is a trade-off between exercise intensity and duration. It appears that lower-intensity exercise is offset by an increased duration of training.

With regard to exercise, the term "aerobic" refers to the use of oxygen in supplying the working muscles with energy. Your muscles function and do their thing because of an energy reserve in them called adenosine triphosphate, or ATP for short. This is a special chemical substance necessary for all muscle contractions. No ATP, no muscle contraction. ATP can be supplied both without oxygen (anaerobic) and with oxygen (aerobic) via different metabolic pathways. The aerobic pathways are used to a large extent at lower intensities of exercise and utilize fats as their main source of fuel. When exercise can be maintained at a given intensity for longer than 15 minutes, the intensity is usually within the aerobic zone and fat is the primary fuel source.

Heart-rate monitoring is probably the most widely used method for exercise prescription of healthy adults and athletes. The variations in heart rate correlate with the variations in exercise intensity for aerobic forms of exercise. Under submaximal load the heart rate of a healthy person increases with the increase in oxygen consumption and exercise intensity; therefore, heart-rate monitoring can determine the intensity and aerobic stress an individual is under.

Numerous aerobic exercise machines come equipped with heart-rate monitors for ease in measuring exercise intensity, and by monitoring the exercise intensity through the heart-rate response, the exercise can be better controlled to avoid under- and/or overtraining. Nineteen eighty-nine Ms. Olympia runner-up Sandy Rid-dell utilized the heart-rate monitor on her Aero-Step stair climber to control her aerobic training during her contest preparation. By measuring her training heart rate, she was able to determine the necessary training intensity for her to achieve cardiovascular benefits and for fat loss. The results of this type of constant monitoring of exercise intensity were apparent to all who saw Sandy's condition at the show.

Working up to a target heart-rate zone is a popular method of determining the proper exercise level. Until recently a given percentage of maximum predicted heart rate was used to determine the optimal intensity to reach when training for aerobic benefits. New research suggests, however, that the zone of training may not be as tight as previously thought and that training outside the "training sensitive zone" may elicit changes similar to those seen when training occurs within the prescribed zone.

For the general population it is recommended that the exerciser work out at an intensity of 70 to 90 percent of maximal heart rate for a duration of 15 to 60 continuous minutes, three to five days per week. Maximum heart rate is established as 220 minus the person's age.

The concept of a training threshold suggests that if you train outside the zone-for example, below the thresh-old-the exercise will not produce any results. Studies done by the UCLA Department of Kinesiology show that training below the threshold at less than 70 percent max HR (Heart Rate) produced results similar to those when subjects trained within the target zone and also above the zone, at greater than 90 percent of max HR. By training below the zone, the athlete is less prone to injury and overtraining. While most athletes tend to train at too high of an intensity and get stale and overtrained, especially during contest preparation, motivation to go out for an easy exercise session is more likely if you know the cardiovascular benefits will be just as great. The important point is that for cardiovascular adaptations and improvements in performance low-intensity aerobic exercise is just as beneficial as high-intensity exercise.

When you do aerobic exercise for purposes of weight control and fat loss, the highest intensity which you can maintain for prolonged periods appears to be the most beneficial. As exercise intensity increases the ratio of carbohydrate (muscle glycogen) burned for energy compared to fat burned increases; but there is no need to avoid high-intensity aerobics for fear that you won't burn fat. Although high-intensity exercise burns a lower percentage of fat during exercise the caloric cost of the exercise session will ultimately determine the amount of fat and weight lost. Recent research shows that low-intensity exercise of long duration is similar to high-intensity exercise of shorter duration at burning fat and promoting weight loss. The fuel source burned during the exercise session is not as critical. Therefore, if you have a set amount of time you can devote to aerobic training, high-intensity training would be more beneficial for losing weight because you can do it in less time.

When performing high-intensity aerobic exercise for weight control, it is important to maintain a high-carbohydrate diet to resupply the muscle glycogen stores burned during the aerobic activity. If the stores of glycogen are not replaced due to too low a caloric intake or an imbalanced diet, training will be limited and fatigue and overtraining will result.

Aerobic exercise intensity should not be a mystery. High-intensity aerobics appears to be beneficial for fat loss, weight control and for those individuals seeking fast results in terms of cardiovascular adaptations. Low-intensity aerobics results in similar cardiovascular adaptations as higher-intensity work; the results may take longer, but there is less risk of injury, overtraining and loss of motivation.

The decision as to exercise intensity is, therefore, yours. You can feel comfortable in knowing that many combinations of intensity/duration are possible to obtain the desired results. So start aerobicizing and enjoy!