Understanding Intervals - Interval Training - Methods - Time-to-Run Training section

Matching training characteristics to physiological changes
Which is "better", Interval Training or Steady State Training? Obviously that is simplistically stated, but I will try to make things more clear as we go. Eight years ago, my master's thesis asked this exact question. One group of rats "volunteered" to run repeated 2 minute high intensity intervals every day (5 days/week), another group ran 60 minutes continuously each day, and a third group served as cage potato controls. We will come back to the results later. I learned from that study and have continued to learn since.

Interval Training Defined

In a dictionary, an interval is probably defined as a period of time or a specified distance. Well, that's true, but for us endurance athletes it means repeated bouts of high intensity exercise with intermittant rest periods. In endurance training circles, no matter what the sport, Interval Training has become a standard practice. Since the 1960's, interval training has come to be thought of as the key to endurance performance success. In some training programs, it accounts for 50-75% of the total training volume. One fellow I know who coaches runners has even written an article espousing "All Intervals, All the Time." After 10 years of research, reading, observing, and training, I think this line of thinking must be evaluated critically, so here goes. I will hit you with information from a lot of different angles, but hopefully what emerges will be a coherent conclusion.

The Physiology of Intermittant Exercise

In exercise physiology research, one of the true "Fathers" of the field is Per Astrand from Sweden. Today, Dr. Astrand is still showing up at International Sports Medicine research meetings at the age of 80 or so. His best known contribution, "Textbook of Work Physiology", co-written with Norwegian Kaare Rodahl and now in its 5th edition or so, remains a "must have" for the student of exercise physiology. In the 60s he performed some simple experiments that still have important training implications regarding the physiological impact of continuous versus intermittant exercise.

In a lab setting, a bicycle ergometer serves as a very useful tool for performing exercise studies. We can precisely control the workload that the cyclist must maintain, and since he/she is sitting still, it is easy to perform an extensive array of physiological measurements, such as heart rate, VO2, blood lactate etc. (I prefer not to dwell on just how extensive!) The following experiments were performed using just such an exercise setup.