Interval training: alternating periods of high- and low-intensity exercise for maximum benefit - includes continuing education test

American Fitness, July-August, 1997 by Kathy Stevens

Over the past few years, there has been a regeneration of interval training techniques within the fitness industry. It involves the alternation of high and low-intensity cardiovascular exercise in specific timed ratios to improve the cardiovascular system. Think of it as adding peaks and valleys to a workout.

For years, athletes used interval training to enhance their physical conditioning and performance in competition. It's now popping up in group exercise and private training sessions as a prime way to increase exercise demands, utilize fat, break training plateaus and reduce steady state boredom.

What is the relevance of adding interval training to the program of the general fitness enthusiast or less fit individual? In the past, we were told harder isn't always better when it comes to choosing the right aerobic intensity. In the '80s, lower training zones were recommended. It was believed less intensity and longer duration would reduce certain exercise risks as well as burn a higher percentage of fat. It is a safe exercise prescription, but we may need to take another look at the fat burning side of this issue.

We know the percentage of fat utilized during an activity may not be as relevant as the total calories burned by the end of the activity. For example, say a person runs for 30 minutes at 50% of his max VO[sub.2], burns 225 calories and utilizes 50% from fat stores or 112.5 fat 315 calories utilizing 40% from fat stores or 126 fat calories. Thus, not only would more total calories be burned by working at a higher intensity but more fat calories (regardless of the percentage drop) would also be utilized. The key is to complete the 30 minutes. If a person is unconditioned and cannot complete 30 minutes of activity at 70% max VO, it is better to lessen the intensity to make the full duration.

Many fit participants unnecessarily decrease their intensity. By including higher interval intensities for brief periods of time, a person can increase caloric outputs while decreasing the duration of the overall workout. Even the less fit participant can increase exercise intensity at a level that is within their capacity for brief bouts. For participants who don't have a lot of time to work out, this may be an efficient option.

It is well-documented that the body responds to interval training in a different way than it does to continuous training. This is not to say that one type of training is better or should be used instead of the other. Both can make important contributions to cardiovascular fitness.

Natural intervals occur when we encounter hills during a walk or run. If you play recreational sports, you probably experience the need for these bursts of intensity. If you have ever been late for a flight and had to rush through an airport while carrying luggage, you have probably felt the peaks and valleys of life's interval exercise demands. Today, interval training is successfully improving the fitness levels o a broader range of participants. If used properly, it can be an excellent way to maximize and increase the benefits of aerobic training. It can cut down on workout time, reduce more body fat than moderate training, and help regular exercisers stay motivated by new results.

Interval training increases aerobic capacity, or the ability to work harder and longer during cardiovascular activities. The ultimate goal of interval training is to push the aerobic and anaerobic systems to their maximum limits. It is important to understand the aerobic is what is used when doing continuous or steady state training. In this type of training, sufficient oxygen can be supplied to meet the demand of the working muscles so you can keep the activity going for extended periods of time; when you are working at these intensities, you are training aerobically. However, as exercise intensity is increased to the point that oxygen demands can no longer be met by the aerobic system, your anaerobic system contributes to the energy requirements of the activity. This is only possible for a short period of time (from 30 to 90 seconds).

True interval training must include a work effort of high intensity followed by a recovery period of low intensity or complete rest. Both bouts combine to make up what is called an interval cycle. The high-intensity work effort should be performed above 85% of maximum ability (220 minus your age), while the low-intensity recovery period needs to bring your heart rate to below 60% max, or lower than typical continuous training levels. Continuous training refers to aerobic work you can comfortably perform for five minutes and longer.

An interval workout focuses exclusively on aerobic and anaerobic cardiovascular training. This should not be confused with circuit training, which involves a variety of exercise bouts that may include cardiovascular, strength training and flexibility work. Interval training ratios of work to recovery vary depending on the fitness level and conditioning goals. More recent programs have also included a broader range of intensity options in order to accommodate less fit participants. It is recommended that when entering a program that includes higher than previously performed intensities to check with a physician for medical clearance.